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R.T. Vanderbilt Co., Inc. v. Hartford Accident and Indemnity Co.

Court of Appeals of Connecticut

March 7, 2017

R.T. VANDERBILT COMPANY, INC.
v.
HARTFORD ACCIDENT AND INDEMNITY COMPANY ET AL.

          Argued March 30, 2016

         Appeal from Superior Court, judicial district of Waterbury, Complex Litigation Docket, Shaban, J.

          Elizabeth J. Stewart and Jacob M. Mihm, pro hac vice, with whom were Rachel Snow Kindseth and, on the brief, Francis J. Brady, Marilyn B. Fagelson, Stephen Hoke, pro hac vice, and David H. Anderson, pro hac vice, for the appellant-cross appellee (substitute plaintiff).

          Wayne S. Karbal, pro hac vice, with whom were Jeffrey J. Tinley, Amita Patel Rossetti and, on the brief, Alan M. Posner, pro hac vice, for the appellees-cross appellants (named defendant et al.).

          Michael J. Smith, pro hac vice, and Bryan W. Petrilla, pro hac vice, with whom was John F. Conway, for the appellees-cross appellants (defendant Mt. McKinley Insurance Company et al.).

          Lorraine M. Armenti, pro hac vice, with whom were Frank H. Santoro, Shayne W. Spencer, pro hac vice, and, on the brief, Kathleen J. Devlin, pro hac vice, and R. Cornelius Danaher, Jr., for the appellees-cross appellants (defendant Continental Casualty Company et al.).

          Michael L. Duffy, pro hac vice, with whom, on the brief, were Michael G. Albano and Amy R. Paulus, pro hac vice, for the appellee-cross appellant (defendant Old Republic Insurance Company).

          Lawrence A. Serlin, pro hac vice, with whom was Laura Pascale Zaino, for the appellees-cross appellants (defendant Pacific Employers Insurance Company et al.).

          Robert M. Flannery, pro hac vice, with whom were William A. Meehan and, on the brief, Alexander J. Mueller, pro hac vice, and Stephen T. Roberts, for the appellees-cross appellants (defendant Certain Underwriters at Lloyd's, London, et al.).

          Lawrence A. Levy, pro hac vice, with whom were Louis B. Blumenfeld and, on the brief, Richard S. Feld-man, pro hac vice, for the appellees-cross appellants (defendant Fireman's Fund Insurance Company et al.).

          Kevin M. Haas, pro hac vice, with whom were Matthew G. Conway and, on the brief, MaryKate J. Geary and Marianne May, pro hac vice, for the appellee-cross appellant (defendant Westport Insurance Corporation).

          Lawrence D. Mason, pro hac vice, with whom were John A. Lee, pro hac vice, and, on the brief, Dwight A. Kern, for the appellee-cross appellant (defendant National Casualty Company).

          Kathleen D. Monnes, with whom was Erick M. San-dler, for the appellees-cross appellants (defendant St. Paul Fire and Marine Insurance Company et al.).

          Timothy G. Ronan and Assaf Z. Ben-Atar filed a brief for the appellee-cross appellant (defendant Employers Mutual Casualty Company).

          John E. Rodewald, pro hac vice, and David A. Slossb-erg filed a brief for the appellee-cross appellant (defendant Munich Reinsurance America, Inc.).

          Todd A. Bromberg and Laura A. Foggan filed a brief for the Complex Insurance Claims Litigation Association as amicus curiae.

          Edward J. Stein, John M. Leonard, pro hac vice, Amy Bach, pro hac vice, and Heather R. Spaide filed a brief for United Policyholders as amicus curiae.

          Lavine, Beach and Bear, Js.

          OPINION

         TABLE OF CONTENTS

         Page

         I. FACTS ...................... 76

         A. Factual and Procedural History . . . . 76

         B. Issues on Appeal ............. 84

         II. GOVERNING LEGAL PRINCIPLES ..... 87

         A. Principles of Insurance Law ...... 87

         B. Complex Asbestos Litigation ...... 92

         C. Standard of Review ........... 93

         III. ALLOCATION OF DEFENSE AND INDEMNITY COSTS .............. 94

         A. Trigger of Coverage ........... 96

         1. Whether There Is Controlling Connecticut Precedent ........ 102

         2. Whether Trigger of Coverage Is Question of Law or Fact, and Whether Expert Testimony of Dr. Kratzke Was Properly Excluded. . . 105

         3. What Trigger of Coverage Theory Governs Long-Tail Asbestos Litigation in Connecticut ....... 118

         B. Unavailability of Insurance Rule . . . . 123

         1. Unavailability Rule .......... 126

         2. Equitable Exception and

         Testimony of Professor Priest . . . . 143

         3. Whether Trial Court Properly

         Applied Unavailability Rule ..... 153

         4. Nonasbestos Particulates ...... 160

         C. Default Date of First Exposure and Pre-1962 Liabilities ............ 168

         1. Allocation of Past Payments under 2002 Allocation Agreement . . 172

         2. Default Date of First Exposure for Pending and Future Actions . . . 181

         D. Mathematical Allocation Formula and Orphan Shares ............ 185

         1. Orphan Shares ............. 189

         2. Maximum Coverage Block ...... 190

         3. Additional Allocation Issues ..... 191

         E. Prospective Application of Court's Rulings ................... 196

         1. Whether Trial Court Intended to Apply its Allocation Rules Prospectively .............. 199

         2. Whether Prospective Only Application Would Be Permissible under Connecticut Law ........ 207

         3. Guidance on Remand ......... 213

         IV. SCOPE OF COVERAGE AND

         POLICY EXCLUSIONS ............. 214

         A. Pollution Exclusions ........... 215

         1. Standard Pollution Exclusion . . . . 216

         2. Nonstandard Pollution Exclusions . 252

         B. Occupational Disease Exclusions . . . 255

         1. Facts .................. 256

         2. Analysis ................. 260

         C. Duty to Defend Under Continental's

         1968-1977 Umbrella Policies ...... 270

         1. Facts .................. 270

         2. Analysis ................. 273

         V. OTHER CLAIMS ................ 283

         A. Admission of Posner Charts ...... 284

         B. Exhaustion of Primary Policies ..... 293

         1. Products Claims ............ 294

         2. Application of 2002

         Allocation Agreement ......... 297

         C. Duty to Defend Under Old

         Republic's Excess Policies ....... 299

         D. Duty to Defend Under Continental's 1965-1968 and 1977-1978 Excess Policies .................. 303

         VI. CONCLUSION ................. 309

         APPENDIX A-PARTIES JOINING

         APPELLATE CLAIMS ................ 310

         The present action arises from thousands of underlying lawsuits alleging injuries from exposure to industrial talc mined and sold by the plaintiff, R.T. Vanderbilt Company, Inc. (Vanderbilt), [1] that purportedly contained asbestos. In this interlocutory appeal, Vanderbilt and the defendants, approximately thirty insurance companies that issued comprehensive general liability insurance policies to Vanderbilt between 1948 and 2008, are seeking, among other things, a declaratory judgment determining their respective obligations with regard to the underlying actions. Through a series of bifurcation orders, the trial court, Shaban, J., divided the trial into four phases, and the case reaches us now, following the second phase of the trial, on the parties' appeals and cross appeals from several decisions of the court. Before the trial proceeds further, the parties ask that we address approximately twenty issues-primarily questions of law-that will significantly impact the adjudication of the remaining trial phases. These issues present a number of questions of first impression in Connecticut and, in some instances, nationally.[2] Although most relate to the methodology by which insurance obligations are to be allocated with respect to long latency asbestos related claims that implicate multiple policy periods, the parties also challenge the trial court's rulings with respect to the interpretation of various scope of coverage and exclusion provisions in the Vanderbilt policies, whether certain of the primary policies have been exhausted, and other evidentiary and miscellaneous issues. As detailed more fully hereinafter, we affirm in part and reverse in part the rulings of the trial court.

         I

         FACTS

         A

         Factual and Procedural History

         The following facts, as found by the trial court, and procedural history are relevant to our resolution of the issues on appeal. Vanderbilt is a Connecticut corporation engaged in the mining and sale of various chemical and mineral products. In 1948, it began to produce industrial talc through its subsidiary, Gouverneur Talc Company. Vanderbilt continued to mine and sell talc until 2008, when it ceased production and sold off the last of its inventory.

         Over the past several decades, thousands of underlying actions have been filed against Vanderbilt in various jurisdictions throughout the United States, many of which remain pending. Those actions alleged that talc and silica mined and sold by Vanderbilt contained asbestos or otherwise caused diseases that are correlated to asbestos exposure, such as mesothelioma, other asbestos related cancer, and asbestosis (collectively, asbestos related disease). In response, Vanderbilt has taken the position that its industrial talc does not contain asbestos. From the time that it started mining talc, Vanderbilt purchased or attempted to purchase primary and secondary comprehensive general liability insurance to cover the defense and indemnity costs of asbestos related claims.

         Vanderbilt brought the present action against several insurance companies that issued it primary insurance policies between 1948 and 2008: defendant Hartford Accident & Indemnity Company (Hartford); defendant American International Specialty Lines Insurance Company (American International); and defendants Continental Casualty Company, Columbia Casualty Company, and Continental Insurance Company (collectively, Continental). Vanderbilt alleged, among other things, that Hartford and Continental (primary insurers) had breached their contractual obligations to pay their proper shares of defense and indemnity costs in the underlying actions. Vanderbilt also sought a declaratory judgment as to the parties' respective rights and responsibilities under the policies at issue.

         Continental subsequently filed a third party complaint against various insurance companies that had provided secondary coverage-umbrella or excess[3]- to Vanderbilt during the time that it was in the talc business. Those defendants, as well as other secondary insurers later made parties to the case, (collectively, secondary insurers) include: ACE Property & Casualty Insurance Company; American Insurance Company; Arrowood Indemnity Company; Century Indemnity Company; Employers Mutual Casualty Company; Everest Reinsurance Company (Everest); First State Insurance Company; Fireman's Fund Insurance Company (Fireman's); Government Employees Insurance Company (GEICO); Harbor Insurance Company; Mt. McKinley Insurance Company (Mt. McKinley); Munich Reinsurance America, Inc., formerly known as American Reinsurance Company; National Casualty Company (National Casualty); National Union Fire Insurance Co. of Pittsburgh, PA; Old Republic Insurance Company (Old Republic); Pacific Employers Insurance Company (Pacific); Royal Indemnity Company; St. Paul Fire and Marine Insurance Company; Travelers Casualty and Surety Company, formerly known as Aetna Casualty and Surety Company; Twin City Fire Insurance Company; Westport Insurance Corporation; Zurich International Ltd.; and Certain Underwriters at Lloyd's, London (Lloyd's), Certain London Market Insurance Companies, American International Underwriters Insurance Company, and Granite State Insurance Company (collectively, London insurers). Vanderbilt thereafter brought direct claims against these third party secondary insurers.

         Vanderbilt's operative complaint contains six counts.[4] In the first count, Vanderbilt sought a declaratory judgment regarding Continental's duty to defend and indemnify it in the underlying actions. The same declaratory relief was sought as to Hartford (count two) and the secondary insurers (count five). Vanderbilt also asserted breach of contract claims against Continental (count three), Hartford (count four), and certain secondary insurers (count six), claiming that the insurers had failed to fully defend and indemnify it against the underlying claims.

         Prior to the start of trial, the trial court issued a series of scheduling orders, pursuant to which it separated the trial into four phases. In the first two phases, which were tried to the court and have been completed, the court addressed Vanderbilt's declaratory judgment claims and related counterclaims and cross claims. The primary issue before the court in those phases was how insurance obligations are to be allocated with respect to long latency[5] asbestos related claims alleging injuries that occur over the course of years or even decades and, therefore, potentially implicate multiple insurance policy periods. Specifically, in Phase I, the court addressed the question of how defense costs for the underlying actions were to be allocated as between Vanderbilt and its insurers. That required a determination of (1) the periods during which the defendants' insurance policies were in effect and (2) whether Vanderbilt should be treated as self-insured for any period so as to create an equitable obligation to contribute to the costs of its defense. In Phase II, the court considered the same questions with respect to indemnity costs. In that phase, the court also issued rulings with respect to the meaning of various policy provisions, the exhaustion of Vanderbilt's primary policies, and related issues. In Phase III of the trial, which also will be tried to the court, the court plans to adjudicate the defendants' claims for recovery of overpayment of insurance costs. In Phase IV, Vanderbilt's breach of contract claims against its insurers are to be tried to a jury.

         In addressing the allocation questions in Phases I and II, the trial court proceeded on the assumption that Connecticut follows a pro rata, time-on-the-risk approach to allocating insurance obligations in long-tail cases. See footnote 5 of this opinion. Under that allocation scheme, the court assumed that a victim of asbestos related disease suffers continuous injuries commencing at the time of initial exposure to asbestos and extending until disease manifests, and, therefore, that defense and indemnity costs must be allocated across all of the insurance policies on the risk (i.e., potentially liable) during that period (allocation block). The court further assumed that (1) the policyholder is responsible for a pro rata share of costs for any period during which it is uninsured or underinsured (proration to the insured), including so-called ‘‘orphan share'' periods covered by policies that were lost, destroyed, or issued by insurers that subsequently became insolvent; but (2) Connecticut has embraced an unavailability of insurance exception pursuant to which there is no pro-ration to the insured for periods during which insurance is not available. Applying these principles to the present case, the court held evidentiary hearings during Phases I and II to determine, among other things, whether defense and indemnity insurance coverage, respectively, was available for asbestos related claims between 1948 and 2008 and, if so, whether Vanderbilt availed itself of such coverage.

         In memoranda of decision issued following the first and second phases of the trial, the court found that occurrence based[6] comprehensive general liability insurance covering asbestos related claims was generally available for purchase from 1948 through 1955. Although Vanderbilt had purchased such policies, it was unable to locate them. The court therefore determined that Vanderbilt would be treated as self-insured and required to bear its pro rata share of defense and indemnity costs for that period. From 1956 through 1961, by contrast, Vanderbilt had purchased insurance policies that provided sufficient coverage for asbestos related claims.[7] Accordingly, the court determined that Vanderbilt would not be treated as self-insured for those years. The court also found that, with regard to the period from 1962 through March, 1986, it was undisputed that insurance coverage for asbestos claims was generally available and that Vanderbilt had secured such coverage. Accordingly, Vanderbilt was not treated as self-insured for that period.

         As to the period of 1986 through 2008, the court observed that there was considerable conflicting evidence as to whether coverage for asbestos claims was available to Vanderbilt and whether Vanderbilt in fact obtained adequate coverage. Noting that a flood of asbestos related injury claims had led the insurance industry generally to cease offering policies covering such claims after 1985, the court found that there was insufficient evidence to establish that occurrence based or claims-made policies covering asbestos related disease were available from March, 1986 to March, 1993, or after April, 2007. Accordingly, Vanderbilt was not deemed to be responsible for a pro rata share of costs during those periods, even though it did not carry any coverage for asbestos claims. By contrast, the court found that, although asbestos related coverage was not generally available to companies in the mining and chemical industries at any time after 1985, Vanderbilt was, in fact, able to purchase primary claims-made policies that provided defense-and, in one instance, indemnity-cost coverage for the period of March 3, 1993 through April 24, 2007. Because the court found that Vanderbilt was knowingly underinsured during that period of time, it concluded that Vanderbilt would be considered to be self-insured with respect to defense- but not indemnity-cost coverage for that fourteen year period.

         The court also found a gap of $700, 000 in indemnity coverage for the period of March 25, 1978 to April 26, 1978, for which Vanderbilt would be considered to be self-insured. It further found that some of Vanderbilt's insurers were insolvent and determined that Vanderbilt would be treated as self-insured for any liability that would have been allocated to the insolvent insurers.

         With respect to the allocation of costs between Vanderbilt's insurers, the court upheld and enforced a 2002 settlement agreement between Hartford and Continental pursuant to which those primary insurers (1) allocated all obligations related to the underlying claims across their primary policies covering the 1962-1986 period and (2) applied a default date of first exposure of January 1, 1962, for underlying claims for which the actual date of initial exposure to Vanderbilt's talc could not be established. The court also appeared to adopt that default date of first exposure on a prospective basis with respect to pending and future claims against Vanderbilt.

         In light of these findings and conclusions, the court determined that the allocation of defense and indemnity costs would be applied prospectively in the following manner, on the basis of a total potential exposure period of 720 months running from 1948 through 2008:[8] (1) as to defense costs, Vanderbilt would be liable for 265 of the 720 months; (2) as to indemnity costs, Vanderbilt would be liable for ninety-six of the 720 months; and (3) Vanderbilt's responsibility as to both defense and indemnity costs would be adjusted upward for any additional periods when there was a gap in coverage or an insolvent insurer. The court applied these same findings, principles, and allocation rules to underlying actions that alleged harms arising from nonasbestos particulates such as silica. Specifically, the court credited testimony that all of the underlying actions, whether on their face or through subsequent discovery or investigation, involved claims of exposure to asbestos.

         In its Phase II decision, the court also considered the applicability of two types of exclusions contained in certain of Vanderbilt's excess and umbrella policies. The court first addressed the claim by several secondary insurers that the pollution exclusion clauses contained in their policies barred coverage for the underlying actions. The court concluded that the relevant policy language was ambiguous as applied to the asbestos related claims and, therefore, that the exclusions did not preclude coverage. The court also addressed the issue of whether occupational disease exclusions contained in certain secondary policies applied only to claims brought by the policyholder's own employees. The court found that the exclusions were unambiguous and that they did, in fact, bar coverage only for claims brought by Vanderbilt's own employees.

         The court also addressed the issue of whether certain primary policies issued by Hartford and Continental had been exhausted. The court determined, among other things, that Hartford's primary policies for the period of March 3, 1977 to March 3, 1986, and Continental's primary policies for the period of January 1, 1968 to March 3, 1977, had been exhausted and that the liability of any umbrella or excess carriers sitting above those policies would be determined consistently with established pro rata allocation principles.

         Finally, in a separate evidentiary proceeding that was requested by the parties prior to the commencement of the Phase II trial, the court agreed to rule on the issue of whether an umbrella coverage provision contained in Continental's secondary policies covering the period from January 1, 1968 to May 17, 1977, obliged that insurer to defend the underlying claims. The court concluded that Continental had no duty to defend Vanderbilt or to pay for defense costs under those policies. At that time, the court declined to address claims relating to Continental's defense obligations under its 1965- 1968 and 1977-1978 secondary policies or to make a determination as to Old Republic's defense obligations.

         Following the completion of the Phase II trial, Vanderbilt and several defendants filed appeals and cross appeals, challenging approximately twenty of the court's conclusions and findings.[9] Additional facts will be set forth as necessary.

         B

         Issues on Appeal

         On appeal, Vanderbilt raises the following issues: 1. Did the court properly hold Vanderbilt responsible for a pro rata share of defense costs for the period of March 3, 1993 through April 24, 2007? 2. Did the court apply the correct mathematical formula in calculating Vander-bilt's pro rata share of defense and indemnity costs? 3. Did the court properly determine that Continental had no duty to defend under its umbrella policies for the period of January 1, 1968 to May 17, 1977? Vanderbilt also has set forth alternative grounds for affirmance with respect to several of the defendants' cross appeals, which are addressed to the extent necessary in this opinion.

         The issues raised by Mt. McKinley[10] on cross appeal are: 1. Did the court contravene Connecticut's pro rata allocation law when it (a) considered the unavailability of insurance coverage in determining the allocation of defense and indemnity costs (the unavailability rule), and (b) declined to adopt an equitable exception to the unavailability rule in light of Vanderbilt's continued sale of talc through 2008? 2. Did the court properly (a) conclude that all of the underlying claims alleged exposure only to asbestos and (b) fail to hold Vanderbilt responsible for its pro rata share of defense and indemnity costs for nonasbestos particulate claims? 3. Did the court properly determine that the pollution exclusions in the excess and umbrella insurance policies were ambiguous and inapplicable to the underlying actions? 4. Did the court properly determine that, with regard to any claims of injury where the specific dates of first exposure are unknown, the default date of first exposure would be January 1, 1962? 5. Did the court properly apply its findings prospectively from the date of its Phase II decision? 6. Did the court properly preclude the testimony of (a)a medical expert, Robert A. Kratzke, regarding when asbestos related bodily injuries take place, and (b) an insurance expert, George L. Priest, regarding the economic principles of the transfer of risk and the customs and practices in the field of insurance? 7. Did the court properly enforce the 2002 settlement agreement and determine that certain primary policies issued by Hartford and Continental had been exhausted? 8. Did the court properly admit into evidence charts and spreadsheets that were created by Vanderbilt's expert without finding that an exception to the hearsay rule supported their admission? 9. Did the court apply the correct mathematical formula in calculating Vanderbilt's pro rata share of defense and indemnity costs?

         The issue raised by Hartford on cross appeal is: Should the allocation rules that were set forth in the court's Phase II decision be applied retroactively to the date on which its primary coverage was exhausted to assure that Hartford's policy limits are not reopened?

         The issues raised by Continental on cross appeal are: (1) Did the court properly decline to rule that Continental's obligation under its 1965-1968 umbrella-excess policy was only to reimburse Vanderbilt for the defense costs that Vanderbilt had paid for defending claims that implicated Continental's indemnification obligations? (2) Did the court properly decline to rule that Continental did not have a duty to defend Vanderbilt under its 1977-1978 excess policy? (3) Did the trial court properly create allocation blocks of 720 months for defense and indemnification costs?

         The issue raised by National Casualty on cross appeal is: Did the court properly conclude that the occupational disease exclusions in certain umbrella and excess policies apply only to claims brought by Vanderbilt's own employees?

         The issue raised by Old Republic on cross appeal is: Should this court direct the trial court to determine Old Republic's defense obligations prior to commencing any additional phases of the trial?

         For the reasons set forth hereinafter, we reverse the rulings of the trial court (1) holding Vanderbilt responsible for defense costs for the period of March 3, 1993 through April 24, 2007, (2) applying a default date of first exposure of January 1, 1962, for pending and future claims, and (3) concluding that the occupational disease exclusions apply only to claims brought by Vanderbilt's own employees. We also modify in various respects the mathematical formula and allocation method that the court used to apportion defense and indemnity costs between Vanderbilt and its insurers, and we clarify the prospective nature of the court's determinations. Finally, we encourage the trial court, in its discretion, to determine Old Republic's defense obligations prior to commencing any additional phases of the trial. We affirm the rulings of the court in all other respects.

         II

         GOVERNING LEGAL PRINCIPLES

         In the interests of avoiding repetition, we begin by noting certain well established principles that will be relevant to many of the issues in these appeals. In the parts of the opinion that follow, we set forth additional rules of law as relevant to particular claims.

         A

         Principles of Insurance Law

         ‘‘An insurance policy is to be interpreted by the same general rules that govern the construction of any written contract . . . . In accordance with those principles, [t]he determinative question is the intent of the parties, that is, what coverage the . . . [insured] expected to receive and what the [insurer] was to provide, as disclosed by the provisions of the policy. . . . If the terms of the policy are clear and unambiguous, then the language, from which the intention of the parties is to be deduced, must be accorded its natural and ordinary meaning. . . . Under those circumstances, the policy is to be given effect according to its terms.'' (Internal quotation marks omitted.) Lexington Ins. Co. v. Lexington Healthcare Group, Inc., 311 Conn. 29, 37-38, 84 A.3d 1167 (2014).

         ‘‘When interpreting [an insurance policy], we must look at the contract as a whole, consider all relevant portions together and, if possible, give operative effect to every provision in order to reach a reasonable overall result.'' (Internal quotation marks omitted.) Id., 38. ‘‘It is axiomatic that a contract of insurance must be viewed in its entirety, and the intent of the parties for entering it derived from the four corners of the policy.'' (Internal quotation marks omitted.) Springdale Donuts, Inc. v. Aetna Casualty & Surety Co. of Illinois, 247 Conn. 801, 805, 724 A.2d 1117 (1999).

         ‘‘In determining whether the terms of an insurance policy are clear and unambiguous, [a] court will not torture words to import ambiguity where the ordinary meaning leaves no room for ambiguity . . . . Similarly, any ambiguity in a contract must emanate from the language used in the contract rather than from one party's subjective perception of the terms. . . . As with contracts generally, a provision in an insurance policy is ambiguous when it is reasonably susceptible to more than one reading.'' (Internal quotation marks omitted.) Lexington Ins. Co. v. Lexington Healthcare Group, Inc., supra, 311 Conn. 38.

         ‘‘[Words] do not become ambiguous simply because lawyers or laymen contend for different meanings. . . . Words also do not become ambiguous simply because a contract fails to define them; even when undefined, words are not ambiguous if common usage or our case law gives them a single meaning.'' (Citation omitted; internal quotation marks omitted.)New London County Mutual Ins. Co. v. Nantes, 303 Conn. 737, 753, 36 A.3d 224 (2012).

         ‘‘[C]ontext is often central to the way in which policy language is applied; the same language may be found both ambiguous and unambiguous as applied to different facts. . . . Language in an insurance contract, therefore, must be construed in the circumstances of [a particular] case, and cannot be found to be ambiguous [or unambiguous] in the abstract. . . . In sum, the same policy provision may shift between clarity and ambiguity with changes in the event at hand . . . and one court's determination that [a] term . . . was unambiguous, in the specific context of the case that was before it, is not dispositive of whether the term is clear in the context of a wholly different matter.'' (Citations omitted; emphasis omitted; internal quotation marks omitted.) Lexington Ins. Co. v. Lexington Healthcare Group, Inc., supra, 311 Conn. 41-42.

         Our Supreme Court and this court also have recognized certain rules of construction specific to the interpretation of insurance contracts. First, ‘‘[i]t is a basic principle of insurance law that policy language will be construed as laymen would understand it and not according to the interpretation of sophisticated underwriters . . . . [T]he policyholder's expectations should be protected as long as they are objectively reasonable from the layman's point of view.'' (Internal quotation marks omitted.) R.T. Vanderbilt Co. v. Continental Casualty Co., 273 Conn. 448, 462-63, 870 A.2d 1048 (2005); Nationwide Mutual Ins. Co. v. Pasiak, 161 Conn.App. 86, 96, 127 A.3d 346 (2015), cert. granted on other grounds, 320 Conn. 913, 130 A.3d 266 (2016).

         Second, and relatedly, when the plain language of an insurance policy is found to be ambiguous, courts ‘‘apply the contra proferentem rule and interpret a policy against the insurer. . . . Indeed, our interpretation of ambiguous policy language in favor of coverage under the doctrine of contra proferentem has become near axiomatic in insurance coverage disputes.'' (Citation omitted; internal quotation marks omitted.) Connecticut Ins. Guaranty Assn. v. Fontaine, 278 Conn. 779, 788-89, 900 A.2d 18 (2006). ‘‘The premise behind [this] rule is simple. The party who actually does the writing of an instrument will presumably be guided by his own interests and goals in the transaction. He may choose shadings of expression, words more specific or more imprecise, according to the dictates of these interests. . . . A further, related rationale for the rule is that [s]ince one who speaks or writes, can by exactness of expression more easily prevent mistakes in meaning, than one with whom he is dealing, doubts arising from ambiguity are resolvedin favor of the latter. . . . This canon . . . is more rigorously applied in the context of insurance contracts than in other contracts.'' (Citation omitted; internal quotation marks omitted.) Israel v. State Farm Mutual Automobile Ins. Co., 259 Conn. 503, 508-509, 789 A.2d 974 (2002).

         Nevertheless, ‘‘[t]his rule of construction that favors the insured in case of ambiguity applies only when the terms are, without violence, susceptible of two [equally reasonable] interpretations . . . .'' (Internal quotation marks omitted.) Misiti, LLC v. Travelers Property Casualty Co. of America, 308 Conn. 146, 155, 61 A.3d 485 (2013). Moreover, ‘‘the rule [of contra proferentem] should be applied as a tie breaker only when all other avenues to determining the parties' intent have been exhausted'' Connecticut Ins Guaranty Assn v Drown, 314 Conn 161, 195, 101 A.3d 200 (2014) (Rogers, C J, concurring). Accordingly, when a policy provision is facially ambiguous, the court should first apply other tools of construction and, if relevant, consult extrinsic evidence of the parties' intentions before construing the agreement against the drafter.[11]

         Third, with respect to an insurer's duty to defend a claim brought against the insured, we note that ‘‘[u]nder the well established four corners doctrine, the duty to defend is broader than the duty to indemnify.'' (Internal quotation marks omitted.) Travelers Casualty & Surety Co. of America v. Netherlands Ins. Co., 312 Conn. 714, 739, 95 A.3d 1031 (2014) (Netherlands). ‘‘[A]n insurer's duty to defend [is to be] determined by reference to the allegations contained in the [underlying] complaint. . . . [T]he obligation of the insurer to defend does not depend on whether the injured party will successfully maintain a cause of action against the insured but on whether he has, in his complaint, stated facts which bring the injury within the coverage. If the latter situation prevails, the policy requires the insurer to defend, irrespective of the insured's ultimate liability. . . . Hence, if the complaint sets forth a cause of action within the coverage of the policy, the insurer must defend. . . . On the other hand, if the complaint alleges a liability which the policy does not cover, the insurer is not required to defend. . . . Thus, the duty to defend is triggered whenever a complaint alleges facts that potentially could fall within the scope of coverage ....

         ‘‘Despite the breadth of this approach, we have recognized the necessary limits of this rule, as we will not predicate the duty to defend on a reading of the complaint that is . . . conceivable but tortured and unreasonable. . . . Thus, although an insurer is not excused from its duty to defend merely because the underlying complaint does not specify the connection between the stated cause of action and the policy coverage . . . the insurer has a duty to defend only if the underlying complaint reasonably alleges an injury that is covered by the policy.'' (Citations omitted; emphasis omitted; internal quotation marks omitted.) Misiti, LLC v. Travelers Property Casualty Co. of America, supra, 308 Conn. 155-56.

         B

         Complex Asbestos Litigation

         In the parts of the opinion that follow, we discuss at length the legal rules that govern insurance disputes arising from third party claims alleging long-tail asbestos related diseases. At the outset, however, we recognize that the unique logistical, jurisprudential, and financial challenges posed by asbestos litigation; see American Special Risk Ins. Co. v. A-Best Products, Inc., 975 F.Supp. 1019, 1020-21 (N.D. Ohio 1997), aff'd, Docket Nos. 97-3919, 97-3920, 97-4004, 1998 WL 833750 (6th Cir. November 19, 1998) (decision without published opinion, 166 F.3d 1213');">166 F.3d 1213 [6th Cir. 1998]); require that courts adopt rules that, while principled and fair, also are pragmatic and easily administered. See In re School Asbestos Litigation, 789 F.2d 996, 1011 (3d Cir.) (highly unusual nature of asbestos litigation requires novel and flexible solutions), cert. denied sub nom. National Gypsum Co. v. School District of Lancaster, 479 U.S. 915, 107 S.Ct. 318, 93 L.Ed.2d 291 (1986), and cert. denied sub nom. Celotex Corp. v. School District of Lancaster, 479 U.S. 852, 107 S.Ct. 182, 93 L.Ed.2d 117 (1986); Continental Casualty Co. v. Synalloy Corp., 667 F.Supp. 1523, 1538 (S.D. Ga. 1983) (endeavoring to provide guidance ‘‘carefully, methodically and with an eye toward practical solutions''); Owens-Illinois, Inc. v. United Ins. Co., 138 N.J. 437, 477-78, 650 A.2d 974 (1994) (asbestos related injury cases ‘‘demand special attention . . . [and] specialized treatment''); Champion Dyeing & Finishing Co. v. Centennial Ins. Co., 355 N.J.Super. 262');">355 N.J.Super. 262, 271, 810 A.2d 68 (App. Div. 2002) (Champion) (allocation mechanism must be efficient and administratively manageable). We consider the issues raised by the present appeals from that perspective.

         C

         Standard of Review

         Unless otherwise noted, the claims at issue in these appeals concern the proper construction of insurance policies or present other pure questions of law, which we review de novo. See Misiti, LLC v. Travelers Property Casualty Co. of America, supra, 308 Conn. 154. When the trial court has resolved factual disputes that underlie coverage issues, however, those findings are reviewable on appeal subject to the clearly erroneous standard. National Grange Mutual Ins. Co. v. Santaniello, 290 Conn. 81, 90, 961 A.2d 387 (2009). ‘‘Such a finding of fact will not be disturbed unless it is clearly erroneous in view of the evidence and pleadings in the whole record . . . . [A] finding is clearly erroneous when there is no evidence in the record to support it . . . or when although there is evidence to support it, the reviewing court on the entire evidence is left with the definite and firm conviction that a mistake has been committed. . . . Thus . . . [i]t is within the province of the trial court, when sitting as the fact finder, to weigh the evidence presented and determine the credibility and effect to be given the evidence. . . . Credibility must be assessed . . . not by reading the cold printed record, but by observing firsthand the witness' conduct, demeanor and attitude. . . . An appellate court must defer to the trier of fact's assessment of credibility because [i]t is the [fact finder] . . . [who has] an opportunity to observe the demeanor of the witnesses and the parties; thus [the fact finder] is best able to judge the credibility of the witnesses and to draw necessary inferences therefrom.'' (Citation omitted; internal quotation marks omitted.) Id., 90-91.

         Last, ‘‘[t]he standard under which we review evidentiary claims depends on the specific nature of the claim presented. . . . To the extent a trial court's admission of evidence is based on an interpretation of [law], our standard of review is plenary. . . . We review the trial court's decision to admit evidence, if premised on a correct view of the law, however, for an abuse of discretion.'' (Citations omitted; internal quotation marks omitted.) Statewide Grievance Committee v. Burton, 299 Conn. 405, 415, 10 A.3d 507 (2011). When ‘‘a trial court's admission of evidence is based on an interpretation of the [Connecticut] Code of Evidence, our standard of review is plenary.'' State v. Saucier, 283 Conn. 207, 218, 926 A.2d 633 (2007).

         III

         ALLOCATIONOFDEFENSE ANDINDEMNITY COSTS

         We begin by addressing a series of claims raised by Vanderbilt and certain of the defendants challenging various aspects of the methodology that the trial court used to allocate defense and indemnity costs among the parties. Vanderbilt argues on appeal that the trial court improperly held it responsible for defense costs for the period March 3, 1993 through April 24, 2007, when, Vanderbilt contends, defense cost coverage was unavailable to companies with a potential exposure to third party asbestos litigation. For its part, Mt. McKinley[12] contends that the trial court improperly (1) held as a matter of law that the continuous trigger of coverage theory governs long-tail asbestos related disease claims in Connecticut; (2) applied an unavailability of insurance rule without an equitable exception for companies that continued to engage in asbestos related businesses after 1985, and also applied that rule to underlying actions alleging harms arising from exposure to nonasbestos particulates; (3) declined to consider expert testimony with respect to both the trigger of coverage question and the proposed equitable exception to the unavailability rule; (4) set an unreasonable default date of first exposure of January 1, 1962, for underlying actions that did not allege a specific date and enforced a settlement agreement between the primary insurers that applied that default date to claims arising prior to 1962; and (5) applied its findings and allocation rules on a prospective basis. In addition, both Vanderbilt and several of the defendants contend that the trial court applied an incorrect mathematical formula when calculating Vanderbilt's pro rata share of defense and indemnity costs, although Vanderbilt and the defendants challenge different aspects of the court's allocation formula.

         For the reasons presented hereinafter, we agree with Vanderbilt that it should not have been allocated any post-1986 defense costs. We also agree with certain critiques of the trial court's allocation formula, [13] and we clarify the prospective application of the court's decisions. In addition, we agree with Mt. McKinley that it is unreasonable to continue to apply a default date of first exposure of January 1, 1962, to pending and future claims. We otherwise reject the defendants' challenges to the allocation methodology applied by the trial court.

         As we noted in part II B of this opinion, the adjudication of insurance coverage disputes arising from long-tail toxic torts such as asbestos related disease presents a number of complex and unique legal questions. The trial court confronted several of these questions in its Phase I and Phase II decisions, in which the court sought to determine what share of the defense and indemnity costs, respectively, should be borne by Vanderbilt as the insured and what share should be borne by its various insurers. In adopting an allocation methodology, the court addressed four general questions. First, in the case of progressive, long latency diseases such as asbestosis and asbestos related cancers that do not manifest until years or even decades after exposure to a toxic agent, when does injury occur so as to trigger insurance coverage? Second, under a pro rata allocation approach pursuant to which a policyholder is liable for periods when it self-insures, should the policyholder also be held liable for periods when coverage is unavailable? Third, what default date of first exposure should be applied when neither the complaint nor the discovery process reveals when an underlying plaintiff was first allegedly exposed to a toxic agent? Fourth, according to what mathematical formula should the respective liabilities of the insured and the various insurers be calculated?

         In this part of the opinion, we address each of these substantive questions, as well as related challenges to the trial court's specific factual findings, legal conclusions, and evidentiary rulings. We also consider whether the findings and conclusions adopted by the trial court, as modified herein, apply to underlying actions alleging harms arising from exposure to nonasbestos particulates such as silica, and to what extent the court's findings and conclusions should be applied on a prospective only basis.

         A

         Trigger of Coverage

         The first task in evaluating the parties' obligations with respect to underlying asbestos actions is to determine what event or events ‘‘trigger'' an insurer's defense and indemnification obligations under the many insurance policies that Vanderbilt has purchased over the years. The trial court concluded that established Connecticut precedent compelled it to adopt a continuous trigger theory, under which every insurance policy in effect from the date a claimant is first exposed to asbestos until the date-often decades later-when the claimant manifests an asbestos related disease is on the risk for defense and liability costs. On appeal, Mt. McKinley argues that (1) the trial court was not bound by Connecticut precedent to adopt any particular trigger theory, (2) the trial court should have allowed expert medical testimony on the trigger issue, and (3) this court should adopt an injury-in-fact trigger theory with respect to asbestos related cancers, [14] under which only those policies in effect when a complainant's condition becomes malignant must bear a share of liability and defense costs. We agree that our Supreme Court has not yet adopted continuous trigger as the law of Connecticut but, for the reasons discussed hereinafter, we adopt that theory of coverage as a matter of law for all asbestos related disease claims.[15]

         Trigger of coverage is a concept used by courts to determine whether and when an event implicates a particular insurance policy. The term ‘‘trigger'' does not appear in any of the policies, but is instead ‘‘a label for the event or events that under the terms of the insurance policy determines whether a policy must respond to a claim in a given set of circumstances.'' (Internal quotation marks omitted.) Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 447; see also A.W. Chesterton Co. v. Massachusetts Insurers Insolvency Fund, 445 Mass. 502, 518, 838 N.E.2d 1237 (2005) (‘‘[t]rigger of coverage is a term of art whereby the court describes what must occur during the policy period for potential coverage to commence under the specific terms of an insurance policy'' [internal quotation marks omitted]).

         The comprehensive general liability policies at issue in the present case typically obligate the issuers to reimburse Vanderbilt for defense and indemnity costs for bodily injuries to third parties caused by an ‘‘occurrence.''[16] For example, one typical policy, a March 3, 1983 umbrella policy written by the Gibraltar Casualty Company (Gibraltar), the predecessor of Mt. McKinley, provides in relevant part: ‘‘[The insurer] will pay on behalf of the [i]nsured the [u]ltimate [n]et [l]oss, in excess of the applicable underlying or retained limit, which the [i]nsured shall become legally obligated to pay as damages because of . . . [p]ersonal [i]njury . . . to which this policy applies, caused by an [o]ccurrence.'' The policy further defines an occurrence as ‘‘an accident, a happening, an event, or a continuous or repeated exposure to conditions which results during the policy period in [p]ersonal [i]njury . . . .'' (Emphasis added.)

         According to the plain language of the policy, then, an insurer is liable only for those costs that result from injuries sustained while the policy is in effect. Indeed, it is black letter law that ‘‘[u]nder a liability policy providing coverage for each [injury] during the policy period, a risk insured against by the policy must occur during the policy period in order for coverage to be triggered.'' 7 S. Plitt et al., Couch on Insurance (3d Ed. Rev. 2013) § 102:23, p. 102-73.

         In the case of common third party liability claims such as premises liability, dog bites, and motor vehicle accidents, there typically is little doubt whether personal injuries alleged to have resulted from an incident originated during a particular policy period. See J. Michaels et al., ‘‘The Avoidable Evils of ‘All Sums' Liability for Long-Tail Insurance Coverage Claims, '' 64 U. Kan.L. Rev. 467, 467 (2015). With respect to progressive, long latency injuries such as asbestos related disease, by contrast, the trial court recognized that it is far more difficult to pinpoint exactly when the alleged injuries occurred and, therefore, whether they trigger coverage under any particular liability policy. See id.; see also Continental Casualty Co. v. Employers Ins. Co. of Wau-sau, 60 App. Div. 3d 128, 144-45, 871 N.Y.S.2d 48 (2008), leave to appeal denied, No. 2009-696, 2009 WL 3428552 (N.Y. October 27, 2009) (decision without published opinion, 13 N.Y.3d 710, 918 N.E.2d 962, 890 N.Y.S.2d 447');">890 N.Y.S.2d 447 [2009]). This is true for a number of reasons.

         First, asbestos exposure has been linked to various different diseases-asbestosis, mesothelioma, and lung cancer, among others-each of which has a distinct etiology, symptomology, and course of progression. See 29 C.F.R. § 1910.1001, App. G; 29 C.F.R. § 1926.1101, App. I; One Beacon American Ins. Co. v. Huntsman Polymers Corp., 276 P.3d 1156, 1159 (Utah App.), cert. denied, No. 20120354, 2012 WL 4466557 (Utah July 30, 2012) (decision without published opinion, 285 P.3d 1229');">285 P.3d 1229 [Utah 2012]); A. Bernstein, ‘‘Asbestos Achievements, ''37Sw.U. L.Rev. 691, 706-707 (2008). A claimant in an underlying action may allege that asbestos exposure resulted in more than one of these diseases, or may fail to specify the precise nature of the injuries alleged. See, e.g., Complaint of Catherine Mesker (alleging that decedent suffered ‘‘as bestosis, carcinoma, pneumoconiosis and emphysema''); Complaint of Antonio Ciaramitaro (alleging only that complainant ‘‘suffers from an ‘asbestos-related disease' ''). Accordingly, it often is difficult to assess at what point the injuries in any particular case are alleged to have commenced and it is almost impossible to generalize across thousands of underlying cases.

         Second, the latency period for asbestos related diseases can be extremely long. Mesothelioma, for example, may not manifest until forty years or more after exposure. See 29 C.F.R. § 1926.1101, App. I; Ricigliano v. Ideal Forging Corp., 280 Conn. 723, 744, 912 A.2d 462 (2006). In addition, many individuals who develop asbestos related disease are repeatedly exposed to multiple sources of asbestos over the course of several years or more. See Continental Casualty Co. v.Employers Ins. Co. of Wausau, supra, 60 App. Div. 3d 144. It is not well established what threshold of exposure must be reached in order for disease to manifest. See Keene Corp. v. Ins. Co. of North America, 667 F.2d 1034, 1040 (D.C. Cir. 1981), cert. denied, 455 U.S. 1007, 102 S.Ct. 1644, 71 L.Ed.2d 875 (1982); A. Bernstein, supra, 37 Sw. U. L. Rev. 707. This makes it exceedingly difficult, when all that is known is the date that disease manifested or was diagnosed, to back in to a reasonable estimate of the date at which exposure crossed a threshold level of toxicity. See Continental Casualty Co. v. Employers Ins. Co. of Wausau, supra, 148; see also Green v. General Dynamics Corp., 245 Conn. 66, 72-73, 712 A.2d 938 (1998) (explaining that exact time of origin of occupational diseases is necessarily obscure); 7 S. Plitt et al., supra, § 102:24, p. 102-84 (‘‘[t]he problem of determining when the coverage-triggering event occurred is particularly acute where there is a lengthy interval between an injury from a wrongful act and the manifestation of that injury in ascertainable damage which forms the basis for a claim against the insured'').

         Third, and perhaps most importantly, the etiology of the primary asbestos related diseases is complex and not yet fully understood. See A. Bernstein, supra, 37 Sw. U. L. Rev. 707. As we explain more fully hereinafter, there continues to be a split of opinion, even among medical experts, as to what constitutes the initial ‘‘injury'' in these types of cases.

         The determination of which insurance policies are triggered in a case alleging asbestos related disease thus requires that courts answer two questions. First, at what point or points can the injury be said to occur? If, for example, a hypothetical complainant inhales asbestos dust in year one; subsequently undergoes a series of asbestos related genetic mutations; develops a latent malignancy in year fifteen; and is diagnosed with asbestos related lung cancer in year twenty when symptoms begin to appear; should any defense and indemnity costs be allocated to the insurance policy or policies in effect in (1) year one, when the complainant was first exposed to asbestos (the exposure or initial exposure theory), (2) year fifteen, when malignancy emerged (the injury-in-fact theory), (3) year twenty, when the disease manifested and was diagnosed (the manifestation theory), or (4) every year from one through twenty (the continuous or multiple trigger theory)? Second, should that question be resolved by a reviewing court as a matter of law, or by the trier of fact as a question of medical fact?

         1

         Whether There Is Controlling Connecticut Precedent

         Before we address these questions, we briefly consider Vanderbilt's contention that they already have been resolved by our Supreme Court. Specifically, Vanderbilt asserts that, in Security Ins. Co. of Hartford v. Lumbermens Mutual Casualty Co., 264 Conn. 688, 826 A.2d 107 (2003) (Security), the Supreme Court adopted the continuous trigger theory as the law governing all asbestos related bodily injury claims in Connecticut. Mt. McKinley counters that the question of trigger was not before the Supreme Court in Security and remains unresolved. We agree with Mt. McKinley.

         Like the present case, Security involved a dispute over the proper method of allocating defense costs for underlying asbestos actions alleging long latency bodily injury claims that potentially implicated multiple insurance policies. Id., 690. The trial court in Security concluded that, under Connecticut law, insurance costs for long-tail injuries should be allocated according to a pro rata method rather than a so-called ‘‘all sums'' or ‘‘joint and several'' liability method. Id., 697-98. In jurisdictions that follow an all sums approach, the policyholder is permitted to collect its total liability, up to the policy limit, under any policy in effect during the periods in which the progressive injuries occurred. In re Viking Pump, Inc., 27 N.Y.3d 244, 255-56, 52 N.E.3d 1144, 33 N.Y.S.3d 118 (2016). The burden then falls to the insurer from whom the policyholder chooses to recover to seek contribution from the insurers that issued other triggered policies. Id. Under pro rata allocation, by contrast, losses are allocated equally at the outset between all of the years (or months, etc.) during which the long-tail injuries occurred. Id., 256. Another key difference between the two allocation methods is that, under the all sums approach, a policyholder bears no liability for periods of injury during which it is uninsured; it is free to call upon one triggered policy and then the next, seriatim, until all of the policy limits are exhausted. See Security Ins. Co. of Hartford v. Lumbermens Mutual Casualty Co., supra, 264 Conn. 701-702. In most pro rata jurisdictions, by contrast, the insured is liable for costs attributable to injuries that occurred during any period when it was uninsured or underinsured. Id.

         Having adopted a pro rata allocation scheme, the trial court in Security further concluded that (1) the underlying litigation ‘‘involved a continuous trigger situation such that all asbestos related injury policies issued during the extended exposure period have been triggered for coverage and all companies that issued such policies are responsible for defense costs''; (internal quotation marks omitted) id., 696-97; and (2) defense costs should be prorated to the insured with respect to periods for which the insured had lost or destroyed its policies or otherwise assumed the obligations of an insurer. Id., 690. On appeal, the policyholder did not challenge the former conclusion, but instead challenged only the trial court's adoption of a pro rata allocation scheme. Id., 699-706. Moreover, our Supreme Court, which delineated the four prevailing trigger theories in a footnote, took no position as to whether the trial court had properly adopted the continuous trigger theory. See id., 697 n.12. Because the question of trigger was not at issue on appeal and the Supreme Court did not opine thereon, we agree with Mt. McKinley that Security does not establish continuous trigger or any other trigger theory as the law of Connecticut. See Dept. of Public Safety v. Freedom of Information Commission, 103 Conn.App. 571, 582 n.10, 930 A.2d 739 (‘‘[i]t is axiomatic that an appellate decision stands only for those issues presented to, and considered by, the court in that particular appeal''), cert. denied, 284 Conn. 930, 934 A.2d 245 (2007).

         We also are not persuaded by Vanderbilt's argument that our Supreme Court adopted the continuous trigger theory in Netherlands. Because Netherlands addressed a fundamentally different sort of underlying claim-the state of Connecticut sued a masonry contractor, among other defendants, for water damage resulting from negligent construction of a public building-it is not clear that any trigger of coverage theory adopted in that case would govern long-tail personal injury claims such as asbestos related disease. See John Crane, Inc. v. Admiral Ins. Co., 991 N.E.2d 474 ( Ill. App. 2013) (noting that different trigger theories may apply to personal injury and property damage claims), leave to appeal denied, Nos. 116207, 116209, 116211, 2013 WL 5497780, 5497781, 5497785 (Ill. September 25, 2013) (decisions without published opinions, 996 N.E.2d 11 and 996 N.E.2d 14');">996 N.E.2d 14 [Ill. 2013]); Trustees of Tufts University v. Commercial Union Ins. Co., 415 Mass. 844, 855, 616 N.E.2d 68 (1993) (similar). In any event, we do not read Netherlands as having definitively adopted any particular trigger theory.

         In Netherlands, the defendant insurance company maintained that our Supreme Court had adopted an initial exposure trigger theory in Security, whereas the plaintiff contended that Security adopted an injury-in-fact theory. Travelers Casualty & Surety Co. of America v. Netherlands Ins. Co., supra, 312 Conn. 752. Consistent with our own analysis, however, the Supreme Court clarified that, in Security, it merely ‘‘upheld a pro rata allocation based on the trial court's unchallenged decision that the continuous trigger theory applied''; (emphasis added) id., 754-55; and did not endorse one exposure theory to the exclusion of others. Id., 754 n.33. It is also noteworthy that, in resolving the dispute in favor of the plaintiffs, our Supreme Court stated that ‘‘[the plaintiffs argue] that in [Security] we actually adopted . . . an injury-in-fact trigger, under which progressive injuries that span multiple policy periods trigger all policies in effect during the progression of the injury . . . . We agree with [the plaintiffs], and conclude that, consistent with the continuous trigger situation addressed in Security . . . the trial court properly allocated the insurers' pro rata shares . . . .'' (Emphasis added; internal quotation marks omitted.) Id., 752-53. The court did not explain why it appeared to conflate two distinct trigger theories-injury-in-fact and continuous trigger-nor did it purport to adopt, or provide any rationale for adopting, one theory or the other as the law of Connecticut. Accordingly, we believe that the most reasonable interpretation of the Netherlands decision is that our Supreme Court merely (1) upheld the trial court's use of an injury-in-fact trigger theory as reasonable under the specific facts of that case and (2) recognized that the application of an injury-in-fact trigger by the trial court in Netherlands was not inconsistent with the application of a continuous trigger theory by the trial court in Security.[17] We therefore agree with Mt. McKinley that whether continuous trigger or some other trigger theory should govern asbestos related insurance claims remains an open question in Connecticut.

         2

         Whether Trigger of Coverage Is Question of Law or Fact, and Whether Expert Testimony of Dr. Kratzke Was Properly Excluded

         Although the parties focus their attention on the question of which trigger theory should apply to long-tail personal injury claims, we begin our analysis with the predicate question of whether that question is one of fact or law. We conclude that the efficient administration of justice requires that, like the majority of our sister courts, we resolve the question as a matter of law, at least with respect to asbestos related claims.[18]For this reason, we conclude that the trial court properly excluded expert testimony on the subject.

         The following additional procedural facts are relevant to our resolution of this issue. During both the Phase I and Phase II trials, Mt. McKinley offered the expert testimony of Robert Kratzke, a medical oncologist, to educate the court about recent advances in scientific knowledge regarding the etiology of cancer, including diseases such as lung cancer and mesothelioma that are strongly correlated to asbestos inhalation. According to Mt. McKinley's expert disclosure and proffers, Dr. Kratzke would have testified as follows. Since approximately the turn of the millennium, much has been learned about the genesis and progression of cancer. Cancer is largely a disease of acquired genetic mutations. Everyone experiences numerous genetic mutations as a result of random gene transcription errors during the ordinary cell division process, and people also can experience mutations as a result of exposure to carcinogens. The vast majority of mutations caused by asbestos, even mutations to cancer-relevant genes, are not harmful and do not result in injury, sickness, or death. Rather, for cancer to occur there must be multiple mutations to an individual cell line and, in Kratzke's opinion, there is neither injury to the body nor disease until the final cancer-relevant mutation takes place.

         Kratzke further would have testified that it is impossible to determine when a cancerous cell line experienced its first mutation and that, if an individual suffers multiple exposures to asbestos, there is no way to determine whether any particular exposure, including the first or last exposure, caused a cancerous mutation. Finally, he would have testified that, in most cases of mesothelioma, the last necessary mutation that results in malignancy will occur no more than two to five years before the first cancer symptoms appear. For lung cancer, the corresponding period is five to ten years. Therefore, Kratzke would have opined, it is now firmly established that most types of cancer, including those correlated to asbestos exposure, do not go through a lengthy latency period after the cancer comes into existence, as was previously believed. Rather, the lengthy period between initial exposure to a carcinogen and manifestation of disease reflects the fact that initial mutations are not harmful until combined over time with subsequent mutations.

         Vanderbilt filed a motion in limine to exclude Kratzke's testimony, contending that the proffered testimony was both irrelevant and prejudicial. The trial court granted Vanderbilt's motion, ruling that the testimony was either irrelevant or not materially probative of the issues before the court and, therefore, that it would not be of assistance to the court.[19] See Conn. Code Evid. § 7-2 (expert testimony is admissible if it will assist trier of fact in understanding evidence or determining facts in issue); Conn. Code Evid. § 7-3 (expert testimony as to ultimate issue admissible when trier needs expert assistance). The court's ruling appears to have been predicated on its belief that, in Security, our Supreme Court adopted a continuous trigger theory as the law of Connecticut and, therefore, there was no reason for the court to entertain expert testimony that might provide factual support for alternative trigger theories.

         On appeal, Mt. McKinley contends that the trial court committed reversible error by precluding Kratzke's testimony. As previously discussed, Mt. McKinley maintains that our Supreme Court has not adopted any particular trigger theory as the law of Connecticut. It further argues that, for there to be any insurance coverage for anunderlying claim, Vanderbilt bears the burden of establishing, as a matter of fact, that a particular policy was triggered by bodily injury during the policy period. More generally, Mt. McKinley argues that it would be improper for us to adopt a particular trigger theory as a matter of law, divorced from contemporary scientific knowledge of the etiology and progression of asbestos related diseases. For example, if Kratzke is correct that initial exposure to asbestos fibers does no damage to the human body, and that mesothelioma does not develop until two to five years before the disease manifests, then, in Mt. McKinley's view, it would be improper for us to adopt a theory, such as initial exposure or continuous trigger, that imposes liability on insurers who provided coverage (1) at the time of initial exposure and (2) more than five years prior to the manifestation of disease. A corollary of this argument is that, in adopting a trigger of coverage theory to resolve asbestos related insurance claims, it would be improper for us to rely on decisions that other courts reached decades ago, on the basis of medical and scientific models that may since have been debunked.

         Mt. McKinley's arguments are not without merit and, as we have explained; see part III A 1 of this opinion; we agree that the trial court was mistaken in concluding that it was compelled by Security to apply a continuous trigger theory. Nevertheless, we are not persuaded that the question of which trigger theory applies to the underlying claims is a factual question about which Kratzke's testimony would have proved enlightening.[20]Two questions are intertwined in Mt. McKinley's argument. First, is it appropriate for an appellate court to adopt a trigger of coverage theory as a matter of law, rather than allowing the question of when injury occurs to be resolved as a matter of fact, on a case-by-case basis, in light of the best available scientific evidence? Second, if we answer the first question in the affirmative, does current scientific knowledge regarding the etiology and progression of asbestos related diseases place any restrictions on which theory or theories we may adopt? We address each question in turn.

         a

         Whether Trigger of Coverage Is Question of Law or Fact

         Mt. McKinley contends that the process by which inhalation of asbestos fibers leads to various forms of cancer that are not diagnosable until decades later and, in particular, whether any actual injury occurs upon initial exposure, is a question of fact that is beyond the knowledge of any layperson and that can be proven only by evidence and expert testimony. For this reason, it argues, the question of what trigger theory should govern comprehensive general liability policies as applied to long-tail asbestos related claims also is one of fact that requires expert testimony. We disagree.

         We begin with the standard of review. ‘‘Expert testimony should be admitted when: (1) the witness has a special skill or knowledge directly applicable to a matter in issue, (2) that skill or knowledge is not common to the average person, and (3) the testimony would be helpful to the court or jury in considering the issues.'' (Internal quotation marks omitted.) Weaver v. McKnight, 313 Conn. 393, 405-406, 97 A.3d 920 (2014). ‘‘We review a trial court's decision to preclude expert testimony for an abuse of discretion. . . . We afford our trial courts wide discretion in determining whether to admit expert testimony and, unless the trial court's decision is unreasonable, made on untenable grounds . . . or involves a clear misconception of the law, we will not disturb its decision.'' (Citations omitted; internal quotation marks omitted.) Id., 405. However, whether, as a general matter, expert testimony is required to support a particular type of claim remains a question of law that we review de novo. See Grimm v. Fox, 303 Conn. 322, 329, 33 A.3d 205 (2012).

         There are three reasons why, in our view, the trial court properly concluded that it was not necessary to hear Kratzke's testimony prior to adopting a trigger of coverage rule for the underlying actions. First, a trigger of coverage rule defines what is meant by the policy terms ‘‘personal injury'' or ‘‘bodily injury'' in the context of a long-tail, progressive disease claim. See Keene Corp. v. Ins. Co. of North America, supra, 667 F.2d 1043-44. It is well established that experts may not be called to instruct the court on the meaning of a nontechnical contract term. See Fuller v. Metropolitan Life Ins. Co., 70 Conn. 647, 677, 41 A. 4 (1898); see also Sagamore Group, Inc. v. Commissioner of Transportation, 29 Conn.App. 292, 299, 614 A.2d 1255 (1992) (definition of term is question of law to be determined by court and about which expert witness is incompetent to testify). In the present case, one typical policy defines a covered injury simply as ‘‘bodily injury, sickness, or disease, '' while another insures against ‘‘bodily injury, mental injury, mental anguish, shock, sickness, occupational disease, non-occupational disease, [and] disability . . . .'' There is no indication that the term ‘‘injury, '' as defined in these policies, is intended to be a medical term of art either generally or with respect to asbestos related claims in particular. Accordingly, in construing the policy language, we must look to the ordinary, dictionary definition of the term. See Heyman Associates No. 1 v. Ins. Co. of Pennsylvania, 231 Conn. 756, 771-72, 653 A.2d 122 (1995) (Heyman). Indeed, Mt. McKinley itself appears to recognize that Kratzke was not qualified to opine as to the meaning of ‘‘injury'' in the Vanderbilt policies.

         Second, to the extent that a background understanding of the nature of asbestos related diseases is helpful in selecting among trigger of coverage theories, both courts and commentators have recognized that expert testimony is not required in this context because the relevant medical facts-that (1) asbestos harms the lungs upon inhalation, (2) mesothelioma and lung cancer represent the culmination of a series of genetic mutations that accumulate over a long period of time, and (3) malignancies emerge and begin to proliferate upon the completion of the last necessary mutation- are now so widely understood and incontrovertible that many courts simply assume their truth when resolving the trigger of coverage question. See, e.g., Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 453-54; D. Ramsey, ‘‘The Trigger of Coverage for Cancer: When Does Genetic Mutation Become ‘Bodily Injury, Sickness, or Disease'?, '' 41 Santa Clara L. Rev. 293, 307-28 (2001). Because Kratzke's proffered testimony was fully consistent with the accepted understanding of the etiology and progression of asbestos related disease, it was reasonable for the trial court to conclude, in the exercise of its discretion, that no useful purpose would be served by its admission.

         This conclusion is bolstered by the fact that, among those courts that have considered expert testimony on the question, radically different conclusions have been drawn from substantially similar medical evidence. Compare, e.g., Eagle-Picher Industries, Inc. v. Liberty Mutual Ins. Co., 682 F.2d 12, 19 (1st Cir. 1982) (adopting manifestation trigger theory), cert. denied sub nom. Froude v. Eagle-Picher Industries, Inc., 460 U.S. 1028, 103 S.Ct. 1279, 75 L.Ed.2d 500 (1983); Ins. Co. of North America v. Forty-Eight Insulations, Inc., 633 F.2d 1212, 1218-19 (6th Cir. 1980) (Forty-Eight Insulations) (exposure theory), clarified on reh'g, 657 F.2d 814 (6th Cir.), cert. denied, 454 U.S. 1109, 102 S.Ct. 686, 70 L.Ed.2d 650 (1981); Zurich Ins. Co. v. Raymark Industries, Inc., 118 Ill.2d 23, 42-44, 514 N.E.2d 150 (1987) (unique triple trigger theory); Continental Casualty Co. v. Employers Ins. Co. of Wausau, supra, 60 App. Div. 3d 128 (injury-in-fact theory).

         Third, resolving the injury issue as a question of fact on a case-by-case basis would create uncertainty and significantly increase litigation costs. See M. Doherty, ‘‘Allocating Progressive Injury Liability Among Successive Insurance Policies, '' 64 U. Chi. L. Rev. 257, 258 (1997). As the United States Court of Appeals for the Sixth Circuit explained in Forty-Eight Insulations, ‘‘[i]n each case where a plaintiff sues an asbestos manufacturer, a hearing could be held to determine at what point the buildup of asbestos in the plaintiff's lungs resulted in the body's defenses being overwhelmed. At that point, asbestosis could truly be said to occur . . . . From then on, all companies [that] insured the manufacturer would be treated as being on the risk . . . .

         ‘‘The only problem with this Solomonian interpretation is that no one wants it. The principal reason is cost. If medical testimony as to asbestosis' origin would have to be taken in each of the thousands of asbestosis cases, the cost of litigation would be prohibitive. This appears to be especially true since many of the asbestosis cases are settled before trial. In addition, it is almost impossible for a doctor to look back and testify with any precision as to when the development of asbestosis crossed the line and became a disease.

         ‘‘The only thing on which all parties agree is that there is a need for us to arrive at an administratively manageable interpretation of the insurance policies- one that can be applied with minimal need for litigation.'' (Footnote omitted; internal quotation marks omitted.) Ins. Co. of North America v. Forty-Eight Insulations, Inc., supra, 633 F.2d 1217-18. For similar reasons, the Sixth Circuit clarified on rehearing that the same trigger theory should apply both to asbestosis and to asbestos related cancers, notwithstanding the different etiologies of those diseases. See Ins. Co. of North America v. Forty-Eight Insulations, Inc., 657 F.2d 814, 815-16 (6th Cir. 1980), cert. denied, 454 U.S. 1109, 102 S.Ct. 686, 70 L.Ed.2d 650 (1981); cf. N. Andrea, ‘‘Exposure, Manifestation of Loss, Injury-in-Fact, Continuous Trigger: The Insurance Coverage Quagmire, '' 21 Pepp. L. Rev. 813, 850 (1994) (absence of unified approach to trigger of coverage theories adversely affects insurers and insureds). A number of other appellate courts also have resolved the trigger issue as a matter of law, without reliance on expert testimony. See, e.g., Commercial Union Ins. Co. v. Sepco Corp., 765 F.2d 1543, 1546 (11th Cir. 1985); A C and S, Inc. v. Aetna Casualty & Surety Co., 764 F.2d 968, 972 (3d Cir. 1985); Keene Corp. v. Ins. Co. of North America, supra, 667 F.2d 1044 n.19, 1047 n.25; Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 457.

         For these reasons, we are persuaded that a trigger of coverage theory may be adopted as a matter of law without the assistance of expert medical testimony. We therefore turn our attention to Mt. McKinley's argument that it was nevertheless improper to exclude Kratzke's testimony because (1) whichever trigger theory we adopt must at least be compatible with current medical research and understanding of the etiology and progression of asbestos related diseases such as mesothelioma and lung cancer and (2) Kratzke's testimony, if credited, would preclude us from adopting several of the prevailing trigger theories.

         b

         Whether Current Medical Knowledge Contradicts Initial Exposure or Continuous Trigger Theories

         We next consider whether, in adopting a trigger theory to govern long-tail asbestos related claims, we are precluded by contemporary medical knowledge from selecting any of the four prevailing theories. Specifically, Mt. McKinley argues that, if Kratzke's testimony had been admitted, it would have been clear that neither the initial exposure nor the continuous trigger theory provides a medically credible account of the injuries that actually occur as a result of asbestos inhalation.[21]Vanderbilt responds that, even if we were to credit Kratzke's testimony, it would still be true, on the basis of the undisputed medical facts, that bodily injury occurs immediately upon inhalation of asbestos fibers and continues to occur until disease manifests. We agree with Vanderbilt and conclude that current medical knowledge does not preclude this court from adopting an initial or continuous exposure theory, as well as an injury-in-fact or manifestation theory.

         Vanderbilt draws our attention to a number of key concessions that Kratzke made during his deposition. Kratzke acknowledged that, under the prevailing medical model, the lungs begin to exhibit an inflammatory response within hours or days of exposure to asbestos fibers. This inflammation occurs in individuals who later develop mesothelioma or asbestos related lung cancer and, importantly, Kratzke opined that the initial inflammation probably plays a role in causing the genetic mutations that begin to appear within a few weeks or months after exposure and ultimately lead to cancer. This process, by which asbestos related precancerous mutations are formed, takes place throughout the entire latency period of the disease. In its expert disclosure, Mt. McKinley also indicated that Kratzke would testify that this process occurs because asbestos fibers trapped in and around the lungs provoke cell division and the release of toxins from macrophages, causing nearby cells to mutate.

         Kratzke also testified in his deposition that, in his view, individual cells cannot, by definition, be injured, because ‘‘injury'' is a term that he reserves for major systemic diseases and traumas. Nevertheless, he acknowledged that other physicians do speak in terms of ‘‘damage'' being done to cellular DNA. He also agreed that the term ‘‘injury'' is too ambiguous to be medically useful when talking about changes to cellular DNA, and he acknowledged that the lung cells of a person who has been exposed to asbestos fibers are not ‘‘normal, '' even during the pre-malignancy period when cancer progenitor cells are accumulating mutations.

         Kratzke's opinions, then, were of two types. Empirically, he conceded that asbestos fibers harm the lungs in various ways, almost from the outset. Asbestos causes tissue inflammation, cellular division, and the release of toxins, all of which contribute to and are a but-for cause of the eventual development of asbestos related malignancies in neighboring cells. Semantically, however, Kratzke indicated that oncologists such as himself would not characterize such harms as ‘‘injuries'' or ‘‘diseases'' until such time as the cellular damage actually manifests as a malignancy.

         As we already have explained, there is no indication that the term ‘‘injury, '' as used in a comprehensive general liability policy, is intended to be a medical term of art, much less a term of art specific to the subspecialty of medical oncology. Moreover, as a number of our sister courts have recognized, and as Kratzke himself appeared to acknowledge, at what point cellular damage caused by a carcinogen such as asbestos begins to qualify as an injury or disease is a matter of perspective even among medical experts. From the standpoint of oncologists such as Kratzke, whose job it is to diagnose and treat active tumors, there is no injury, sickness, or disease until damage goes beyond the cellular level and begins to affect entire organ systems. Kratzke explained that he uses the term ‘‘injury'' only with reference to ‘‘gross injur[ies] such as . . . [when] somebody has had their finger cut off [or] somebody has been in a car accident and tissues have been grossly disrupted.'' By contrast, cellular biologists and pathologists, whose job it is to study cellular structures and functions, recognize that the types of damage that asbestos fibers inflict at the cellular level are also fairly characterized as injur-ies.[22] Because there is no indication that the term ‘‘injury'' as used in a standard form commercial general liability policy is intended to be limited to gross injuries of the type described by Kratzke, we conclude that his testimony as to the distinctive meaning that clinical oncologists place on that and other contract terms would not illuminate our interpretation thereof. Instead, we look to the ordinary dictionary definitions of those terms. See Heyman Associates No. 1 v. Ins. Co. of Pennsylvania, supra, 231 Conn. 772.

         Webster's Third New International Dictionary of the English Language Unabridged (2002) defines ‘‘injury'' as ‘‘an act that damages, harms, or hurts . . . .'' It defines ‘‘sickness'' as ‘‘the condition of being ill . . . a disordered, weakened, or unsound condition . . . a form of disease''; and it defines ‘‘disease'' as ‘‘an impairment of the normal state of the living animal . . . or of any of its components that interrupts or modifies the performance of the vital functions . . . .'' In light of Kratzke's acknowledgment that asbestos fibers cause inflammation, abnormal cellular division, and the release of toxins, and that this ongoing process increases the likelihood that malignancies will develop, we have no difficulty concluding that asbestos exposure damages, harms, hurts, weakens, and impairs the body, beginning at the time of exposure and continuing throughout the latency period until the development of malignancy and the ultimate manifestation of cancer. See Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 454 (rejecting need for medical evidence because ‘‘we are satisfied, like most American jurisdictions, that medical science confirms that some injury to body tissue occurs on the inhalation of asbestos fibers, and that once lodged, the fibers pose an increased likelihood of causing or contributing to disease'').

         Accordingly, we conclude that current medical understanding of asbestos related cancers, to which Kratzke would have testified, is not incompatible with any of the prevailing legal theories of trigger. For that reason, it was not improper for the trial court to conclude, in its discretion, that admission of Kratzke's expert testimony would not assist the court in understanding evidence or determining facts in issue.

         3

         What Trigger of Coverage Theory Governs Long-Tail Asbestos Litigation in Connecticut

         Having concluded that we may adopt, as a matter of law and a question of first impression, any of the four prevailing trigger of coverage theories, we now consider which of those theories should govern the pro rata allocation of insurance obligations with respect to long-tail asbestos litigation in Connecticut. Consistent with the majority of our sister states, [23] we adopt the continuous trigger theory, under which every policy in effect, beginning at the time of initial asbestos exposure and extending through the latency period and up to the manifestation of asbestos related disease, is on the risk for defense and liability costs.

         Courts that apply the continuous trigger theory to extended latency, progressive disease claims typically do so for one or more of three primary reasons, each of which we find persuasive. First, courts have adopted continuous trigger as the theory most compatible with the prevailing understanding of the nature and etiology of asbestosis and asbestos related cancers. As we discussed in part III A 2 b of this opinion, it is widely accepted, [24] and Kratzke's expert testimony would have confirmed, that asbestos fibers become lodged in the lungs upon inhalation and, almost from the start, cause damage of various sorts within the lung tissues: inflammation, the release of toxins, and abnormal cellular division and mutation. Importantly, asbestos fibers, unlike many other carcinogens, remain permanently lodged in the lungs, where they continue tocause injury. See D. Ramsey, supra, 41 Santa Clara L. Rev. 307, 332, 337. Indeed, ‘‘asbestos-related cancers may be almost singularly unique in the degree to which they are initiated and promoted by the continuing presence of the asbestos fibers in the lung.'' Id., 305; see also Armstrong World Industries, Inc. v. Aetna Casualty & Surety Co., 45 Cal.App.4th 1, 37, 52 Cal.Rptr.2d 690 (1996) (‘‘[t]he very quality that has made asbestos useful for so long, its indestructibility, also accounts for the problems that result in asbestos-related disease'' [internal quotation marks omitted]), review denied, 1996 Cal. LEXIS 4708 (Cal. August 21, 1996). Accordingly, from a purely factual standpoint, the continuous trigger theory best reflects the fact that asbestos begins to injure the body on a cellular level within hours or days of initial exposure and contributes to the progressive worsening both of asbestosis and of precancerous conditions until the time that those diseases manifest. See Armstrong World Industries, Inc. v. Aetna Casualty & Surety Co., supra, 48; J.H. France Refractories Co. v. Allstate Ins. Co., 534 Pa. 29, 37, 626 A.2d 502 (1993); see also J. Stempel, ‘‘Assessing the Coverage Carnage: Asbestos Liability and Insurance after Three Decades of Dispute, '' 12 Conn. Ins. L.J. 349, 445 (2006) (‘‘continuous trigger is the logical result of the insurance industry's own adoption of an actual injury trigger combined with the [relentless] ability of asbestos to inflict injury over many years''). Our current knowledge about asbestos related disease, then, is most consistent with the theory that the body is continuously injured by the presence of asbestos and the ongoing progression of disease, from exposure through manifestation.[25]

         The second reason that our sister courts have adopted continuous trigger is that that theory of liability also best expresses what is presently unknown about the progression of asbestos related disease. Kratzke conceded in his deposition that, in any particular case, physicians do not know with certainty: (1) how long after exposure to asbestos the lungs begin to develop inflammation; (2) how long the inflammatory response persists; (3) when precancerous mutations commence; (4) the time frame over which precancerous mutations occur; or (5) how long before diagnosis malignancy develops. As one commenter summarized, ‘‘the issues involve a series of astonishingly complex events that unfold through the interactions of vanishingly infinitesimal subcellular molecules over the course of an entire lifetime.'' D. Ramsey, supra, 41 Santa Clara L. Rev. 299. On a micro level, then, there is much about the progression of asbestos related disease that is not yet fully understood.

         Furthermore, these epistemological gaps are magnified at the macro level, when we are confronted with a class action or action such as the present case, in which many individual lawsuits are implicated. The thousands of claimants in the underlying complaints allege various different asbestos related diseases, each of which has its own etiology and course of progression. It is not always clear from the face of the complaint which disease or diseases are alleged, and some claimants allege that they were exposed to asbestos supplied by multiple underlying defendants, at different times, in varying amounts, and through diverse mechanisms. See, e.g., Complaint of Joseph A. Campo. Underlying actions may be settled without any of these questions being squarely resolved. In most instances, then, we simply will never know exactly when a particular claimant was exposed to a particular policyholder's asbestos, how much of that policyholder's asbestos was inhaled, when that claimant contracted an asbestos related disease or diseases, and the precise relationship between these events. See One Beacon American Ins. Co. v. Huntsman Polymers Corp., supra, 276 P.3d 1159. The continuous trigger theory addresses this conundrum by assuming that, in each case, every exposure contributed to the ongoing worsening of the disease throughout the entire period from initial exposure to manifestation. See J. Michaels et al., supra, 64 U. Kan. L. Rev. 472 (continuous trigger relieves policyholder of burden of proving what share of damages from progressive disease occurred during each policy period); id., 487 (continuous trigger acknowledges uncertainty inherent in long-tail toxic tort claims); see also Ins. Co. of North America v. Forty-Eight Insulations, Inc., supra, 657 F.2d 815 (‘‘[M]any of the underlying plaintiffs' complaints against the manufacturers allege both cancer and asbestosis. To [adopt a fact-based trigger theory that would] treat cancer and asbestosis differently would needlessly complicate settlement and defense of the individual lawsuits. We see no reason to create more difficulties for the parties than already exist in this complicated case.'').

         Third, our sister courts have selected the continuous trigger theory as the fairest and most efficient way to distribute indemnity and defense costs among the various policies in effect over the course of a long latency disease claim. See Keene Corp. v. Ins. Co. of North America, supra, 667 F.2d 1041; Montrose Chemical Corp. v. Admiral Ins. Co., 10 Cal.4th 645, 687, 913 P.2d 878, 42 Cal.Rptr.2d 324 (1995), as modified on denial of reh'g (August 31, 1995); see also Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 451 (‘‘because it encourages all insurers to monitor risks and charge appropriate premiums, the continuous trigger rule appears to be the most efficient doctrine for toxic waste cases'' [internal quotation marks omitted]). A number of jurists and scholars have observed that repeat players in the field of asbestos litigation tend to adopt ‘‘fluctuating positions, '' alternatively advocating for diametrically opposed initial exposure or manifestation theories of trigger ‘‘depend[ing] upon their economic interests in a particular case . . . .'' Keene Corp. v. Ins. Co. of North America, supra, 1058 (Wald, J., concurring in part); accord N. Andrea, supra, 21 Pepp. L. Rev. 850. From an objective standpoint, however, we believe that the fairest and most reasonable approach is to share the burden of defense and indemnity costs among all those policies on the risk over the full course of the development and progression of a claimant's disease. Cf. J. Rawls, A Theory of Justice (1971) pp. 136-42 (just distribution of burdens is that which would be adopted by parties behind ‘‘veil of ignorance'' as to their position in particular case). This approach minimizes the likelihood that any one insurer will be forced to shoulder the full expense for injuries that may predominantly have occurred either long before or long after its policy was in effect. See N. Andrea, supra, 815-16. Relatedly, a number of courts have applied a continuous trigger because that theory maximizes the total resources available for recovery. See Quincy Mutual Fire Ins. Co. v. Bellmawr, 172 N.J. 409, 434, 799 A.2d 499 (2002); 7 S. Plitt et al., supra, § 102:24, pp. 102-109 through 102-111; Note, ‘‘Developments in the Law-Toxic Waste Litigation, '' 99 Harv. L. Rev. 1458, 1578-81 (1986).

         Having thoroughly reviewed the arguments for and against the alternative theories of trigger, we are persuaded to join the majority of our sister courts in adopting continuous trigger as the rule governing long-tail asbestos claims in Connecticut. We believe that continuous trigger best accounts for the progressive nature of asbestos related diseases, as both the layperson and at least some subset of medical professionals would consider the tissue damage and other harms imposed throughout the development of asbestosis and asbestos related cancers to constitute personal or bodily injuries as defined in the standard form commercial general liability policy. We also believe that continuous trigger represents the fairest and most efficient means of resolving and administering complex, multiclaimant asbestos litigation such as the present case. Accordingly, we conclude that the trial court properly applied a continuous trigger in the present case.

         B

         Unavailability of Insurance Rule

         As we discussed in part III A of this opinion, in Security, our Supreme Court adopted a pro rata allocation method for adjudicating long latency loss claims that implicate multiple insurance policies. Security Ins. Co. of Hartford v. Lumbermens Mutual Casualty Co., supra, 264 Conn. 720. Under the pro rata approach, defense and indemnity costs are allocated among insurers on the basis of their time on the risk, but are allocated (prorated) to the insured for periods during which the insured lost or destroyed its policies or was otherwise uninsured or underinsured. See id. In this part of the opinion, we address the parties'[26] arguments as to whether costs should be prorated to the insured for periods when it was uninsured not by choice or negligence but because insurance coverage was unavailable. Mt. McKinley contends that there is no authority under Connecticut law for an unavailability of insurance exception to the pro rata allocation method and, therefore, that the trial court improperly exempted Vanderbilt from liability for much of the post-1985 period.[27] In the alternative, Mt. McKinley argues that, if we adopt an unavailability rule, we also should adopt an equitable exception to that rule pursuant to which companies that continued to engage in asbestos related business after 1985, when insurance coverage for third party asbestos claims became generally unavailable, should not be able to benefit from that rule. At the very least, Mt. McKinley contends, the trial court should have allowed expert testimony on this question. Mt. McKinley also maintains that the trial court improperly failed to hold Vanderbilt responsible for its pro rata share of costs for underlying claims alleging injuries arising from silica, talc, and other nonasbestos particulate minerals. In response, Vanderbilt submits that the trial court adopted the correct legal rules with respect to availability of insurance, but that the court applied those rules improperly in concluding that defense cost coverage was available to Vanderbilt from March 3, 1993 through April 24, 2007. We agree with Vanderbilt.

         The following additional procedural history is relevant to our resolution of these claims. In its Phase I decision, the trial court addressed the question of what insurance coverage block applied to defense costs for Vanderbilt's asbestos related liabilities and for what portions of that coverage block, if any, Vanderbilt should be held responsible. The court proceeded on the assumption that, under Connecticut law, a policy-holder is liable for costs attributed to long-tail losses alleged to have occurred during periods when it was self-insured, underinsured, or uninsured, but that costs should not be prorated to the insured for periods during which coverage for a particular risk cannot be acquired (the unavailability rule).

         Consistent with those principles, the trial court made findings as to whether defense cost coverage for asbestos related claims was available to Vanderbilt from 1948 to 2008 and to what extent Vanderbilt availed itself of such coverage. With regard to availability, the court found that insurance companies regularly offered occurrence based defense cost and indemnity coverage for asbestos related claims until 1985 but that, by 1986, such policies had become generally unavailable to companies such as Vanderbilt that operated in the mining and chemical industries. After 1985, comprehensive general liability coverage generally was available to companies in those industries only on a claims-made basis[28] and only with an asbestos exclusion. Despite finding that asbestos coverage was generally unavailable to companies such as Vanderbilt after 1985, the court ultimately found in its Phase I decision that asbestos related defense coverage was available to Vanderbilt between March, 1993 and April, 2007, during which time Vanderbilt was able to obtain a limited number of primary claims-made policies but was otherwise uninsured for asbestos related claims. Accordingly, and consistent with its understanding of the unavailability of insurance rule, the court concluded that Vanderbilt would be held responsible for defense costs attributable to the March, 1993 through April, 2007, period, but not for the remainder of the post-1985 period when insurance was unavailable. In its Phase II decision, by contrast, the court found that indemnity coverage was unavailable to Vanderbilt throughout more or less the entire 1986-2008 period and, therefore, concluded that Vanderbilt was not responsible for any pro rata share of the indemnity costs for that period. The court applied these same findings with respect to underlying actions alleging harms arising from talc, silica, and other nonasbestos particulates.

         1

         Unavailability Rule

         We begin by addressing Mt. McKinley's argument that our state's appellate courts have never adopted an unavailability of insurance rule and that we should not do so at this time. Although we agree with Mt. McKinley that there is no controlling Connecticut precedent, we conclude, as a matter of first impression, that the trial court properly determined that an unavailability rule comports with the allocation scheme adopted in Security. Accordingly, the trial court did not err in declining to prorate indemnity and defense costs to Vanderbilt for periods during which insurance was unavailable.

         a

         Whether There Is Controlling Connecticut Precedent

         As an initial matter, the parties disagree as to whether our Supreme Court adopted an unavailability of insurance rule in Security. Vanderbilt contends that the court did adopt such a rule, whereas Mt. McKinley maintains that the issue was not before the Supreme Court in that case and that it remains an unresolved question in Connecticut.

         There is no question that the trial court in Security applied an unavailability rule in the context of long-tail asbestos litigation. Relying on Stonewall Ins. Co. v. Asbestos Claims Management Corp., 73 F.3d 1178, 1203 (2d Cir. 1995), modified on denial of reh'g, 85 F.3d 49 (2d Cir. 1996), and Keene Corp. v. Ins. Co. of North America, supra, 667 F.2d 1058 (Wald, J., concurring in part), the court reasoned that long-tail costs are prorated to the insured only because the insured has elected to self-insure and thereby assume a portion of the risk, and that those rationales do not apply when insurance is not available. See Security Ins. Co. of Hartford v. Lumbermens Mutual Casualty Co., Superior Court, judicial district of Hartford-New Britain at New Britain, Docket No. CV-96-0475565S, 1999 WL 545745, *8 (July 12, 1999) (‘‘[t]he element of choice, and in turn, the conscious decision of an insured to assume the risks of being ‘self-insured' is lost if the insured cannot realistically acquire the particular coverage desired''). The court also opined that ‘‘[i]t is inequitable to require an insured to assume defense costs for claims [that] it could not have insured against, when multiple insurers are already obligated to provide the insured with a defense in an action.'' Id.

         On appeal, our Supreme Court held that the trial court had properly applied a pro rata, time-on-the-risk allocation methodology for long-tail asbestos claims that implicate multiple policy periods. Security Ins. Co. of Hartford v. Lumbermens Mutual Casualty Co., supra, 264 Conn. 699. In the course of analyzing the allocation issue, the Supreme Court recognized in a footnote that the trial court had cut off the allocation block in 1985, ‘‘at which time asbestos related injury insurance became unavailable . . . .'' Id., 698 n.13. Later in the decision, in a different footnote, the court concluded that the specific allocation methodology applied by the trial court was ‘‘reasonable . . . .'' Id., 720 n.17. The Supreme Court also suggested that the trial court had applied the correct ‘‘equitable principles'' when the trial court concluded that ‘‘[i]t would be grossly inequitable to make [the insurers] bear the financial loss of [the policyholder's] actions or inactions that have rendered [the policyholder] essentially uninsured for a period when asbestos related injury insurance coverage was available.'' (Emphasis added; internal quotation marks omitted.) Id., 720. Vanderbilt reads these portions of Security to mean that our Supreme Court tacitly approved of the trial court's unavailability rule.

         As Mt. McKinley correctly notes, however, the issue of the unavailability of insurance was not before the Supreme Court in Security and the court neither discussed the merits of nor expressly upheld an unavailability rule. Accordingly, any tacit approval of the rule in that opinion was dictum. Moreover, although certain of the rationales that the Supreme Court articulated when adopting a pro rata allocation system would seem to favor an unavailability exception, others are arguably in tension with it. Compare, e.g., id., 719 (emphasizing that policyholder is party best positioned to determine whether it will be, in essence, self-insured) with id. (declining to impose on insurer ‘‘defense costs [that arose] outside of its policy period'' and for which the insured never contracted). Because Security did not expressly adopt or foreclose an unavailability rule, and because language in the decision could reasonably be read to support either position, we conclude that the question remains an open one in Connecticut.

         b

         Whether Connecticut Applies an Unavailability of Insurance Rule

         Of those jurisdictions that have adopted a pro rata, time-on-the-risk allocation scheme, a narrow majority also recognize an unavailability rule.[29] If one includes those jurisdictions that follow the all sums approach, the vast majority of our sister states do not hold an insured accountable for a pro rata share of long-tail losses that occur during periods when insurance is not available. For the reasons that follow, we agree that costs should not be prorated to the insured for periods during which insurance is unavailable.

         The primary rationale that other courts have offered in favor of the unavailability rule is that the justifications that support prorating costs to a policyholder during periods of self-insurance or underinsurance simply do not apply when insurance is not commercially available. Proration to the insured has been justified on the grounds that (1) policyholders should be obliged to accept a share of the risk that they consciously elect to assume by self-insuring; Stonewall Ins. Co. v. Asbestos Claims Management Corp., supra, 73 F.3d 1204; (2) a policyholder would receive an undeserved windfall if it were to reap the benefits of insurance coverage that it deliberately declined to purchase; Wooddale Builders, Inc. v. Maryland Casualty Co., 722 N.W.2d 283, 297 (Minn. 2006); and (3) proration creates an incentive for policyholders to maintain an unbroken chain of adequate insurance coverage, which has the socially desirable benefits of spreading risk, maximizing the resources available to respond to injuries, and ensuring that no single policy or insurer is made to shoulder a disproportionate share of the costs of a long-tail injury. See United States Fidelity & Guaranty Co. v. Treadwell Corp., 58 F.Supp.2d 77, 105 (S.D.N.Y. 1999); Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 472-73; Crossmann Communities of North Carolina, Inc. v. Harleysville Mutual Ins. Co., 395 S.C. 40, 63, 717 S.E.2d 589 (2011). Those rationales are largely inapplicable, however, to situations in which a policyholder desires and attempts to obtain coverage but the insurance industry declines to supply it. See Keyspan Gas East Corp. v. Munich Reinsurance America, Inc., 143 App. Div. 3d 86, 93, 37 N.Y.S.3d 85 (2016).

         Mt. McKinley's principal argument against the unavailability rule is that each insurer contracts to pay only for those losses that occur during its policy period and that the rule improperly allocates to insurers costs attributable to losses arising during uninsured years, for which the insurers have received no premiums. In pressing this argument, Mt. McKinley relies heavily on our Supreme Court's statement in Security that ‘‘[n]ei-ther the insurers nor the insured could reasonably have expected that the insurers would be liable for losses occurring in periods outside of their respective policy coverage periods.'' Security Ins. Co. of Hartford v. Lumbermens Mutual Casualty Co., supra, 264 Conn. 710.

         Our Supreme Court made this statement, however, in discussing policyholders who opt not to procure insurance for extended periods when insurance is readily available; see id., 708-10; and there is no indication that the court intended the statement to apply beyond that context. If the losses at issue in a case such as this resulted from traditional accidents such as a fire or a motor vehicle crash, then it would of course be true that a policyholder could not expect an insurer who provided coverage in, say, 1984 to defend or indemnify losses arising from a 1986 accident. The flaw in Mt. McKinley's reasoning, however, is that it fails to recognize that progressive, long latency injuries such as asbestos related disease are fundamentally different from those sorts of traditional accidents. And because the standard form comprehensive general liability policies that the insurance industry issued prior to 1986 did not anticipate or account for those differences; see Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 468-71; courts have been forced to develop a distinct set of rules to adjudicate long-tail claims.

         One important distinction is that progressive injuries caused by asbestos are indivisible and cumulative. Ins. Co. of North America v. Forty-Eight Insulations, Inc., 451 F.Supp. 1230, 1242 (E.D. Mich. 1978), aff'd, 633 F.2d 1212 (6th Cir. 1980). This means that it is impossible to identify what portion of a claimant's bodily injury actually occurred during which policy period. Many of our sister courts, applying an all sums theory, have concluded that the indivisible nature of progressive injuries means that any insurer on the risk for any period of time can be called upon, at the discretion of the policyholder, to cover the entire claim. Connecticut has adopted a more insurer friendly pro rata allocation system, one that operates on the legal fiction that asbestos related disease occurs in equal increments commencing at the time of initial exposure and culminating with the manifestation of disease. See J. Michaels et al., supra, 64 U. Kan. L. Rev. 473 (continuous trigger theory is legal fiction). But this legal convention does not mean that the policy terms are somehow violated or coverage impermissibly broadened if the allocation rules are structured to (1) encourage policyholders to obtain the broadest possible insurance pool to respond to long-tail claims but (2) not punish those policyholders who, through no fault of their own, are unable to maintain a continuous chain of coverage.

         Mt. McKinley also notes that, although most of the jurisdictions that allocate long-tail insurance costs pro rata also have adopted an unavailability rule, several of our sister courts have rejected such a rule. In particular, Mt. McKinley directs our attention to Boston Gas Co. v. Century Indemnity Co., 454 Mass. 337, 910 N.E.2d 290 (2009) (Boston Gas), and Sybron Transition Corp. v. Security Ins. of Hartford, 258 F.3d 595 (7th Cir. 2001) (Sybron), two of the leading decisions to have rejected an unavailability of insurance rule. Because those cases reject the rule for very different reasons, each warrants attention.[30]

         In Boston Gas, the Supreme Judicial Court of Massachusetts explained why it disagreed with those courts that have held that long-tail losses should not be allocated to a policyholder for periods during which insurance for the risk was not commercially available. Boston Gas Co. v. Century Indemnity Co., supra, 454 Mass. 371. The court reasoned that the unavailability exception ‘‘effectively provides insurance where insurers made the calculated decision not to assume [a] risk and not to accept premiums. In effect, because the policyholder could not buy insurance, it is treated as though it did by passing those uninsurable losses to insured periods. This would not be equitable to insurers if the insured purchased coverage for only a few years where there was protracted damage.'' (Internal quotation marks omitted.) Id., 371-72. Massachusetts' highest court thus raised both a general concern that the unavailability rule fails to honor an insurer's decision not to provide coverage as well as a specific concern that the rule may lead to inequitable results in particular circumstances. We consider each concern in turn.

         The court in Boston Gas, considering the issue from the standpoint of the insurer, concluded that it would be unfair to allocate to an insurer losses that occurred after the insurer determined that it was no longer cost effective to insure against that particular risk. Other courts, by contrast, have looked at the issue from the perspective of the policyholder, concluding that it would not be fair to hold the policyholder responsible for periods during which insurance could not be purchased. See, e.g., Security Ins. Co. of Hartford v. Lumbermens Mutual Casualty Co., supra, 1999 WL 545745, *8; Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 479. As we have explained, however, pro rata, continuous trigger allocation is an artificial judicial construct designed to allocate costs between the various insurance policies that are on the risk during the time over which a single, indivisible injury develops. To our minds, the question of how to allocate uninsurable portions of the allocation block is not so much one of fairness but, rather, of which party should bear the risk that the insurance pool will be terminated if substantial new long-tail risks are identified after significant liabilities already have accrued.

         From an equitable standpoint, either party can justifiably be assigned responsibility for ongoing asbestos related injuries after 1985.[31] The policyholder is the one who allegedly caused the injury and, therefore, who ultimately will be financially responsible should insurance prove insufficient. At the same time, each insurer agreed to write an occurrence based policy that affords ‘‘almost unlimited prospective coverage'' for future costs arising from injuries that take place during the policy period. (Internal quotation marks omitted.) Security Ins. Co. of Hartford v. Lumbermens Mutual Casualty Co., supra, 264 Conn. 692 n.5. Insurers can and do cabin that liability by including relevant exclusions in the policy language and by capping in various ways the limits that they will pay under the policy. See Champion Dyeing & Finishing Co. v. Centennial Ins. Co., supra, 355 N.J.Super. 277. Accordingly, we do not think that it would be fundamentally unfair to hold either the insurers or the policyholder responsible for portions of the allocation block during which insurance is unavailable.

         Perhaps a more fruitful way of approaching the issue is to recognize that it arises only because of a unique confluence of circumstances. We assume-merely for the sake of argument-that, at the time they enter into a contract for a comprehensive general liability policy, both the policyholder and the insurer reasonably believe that the policyholder can safely engage in its chosen line of business, without undue risk of liability. If an unforeseen catastrophe such as a major oil spill occurs in a particular year, it is understood what the respective responsibilities and liabilities of each party will be for the resulting injuries. Similarly, if a well understood long-tail accident such as a gradual chemical leak comes to light, and if the policyholder has been diligent about maintaining continuous insurance coverage, then some policy will be on the risk for each portion of the allocation block. And even if a new risk associated with the business comes to light-say one of the chemical compounds utilized by the policyholder is discovered to be unstable and highly explosive-each party is free to structure its affairs going forward so as to manage that risk; insurers can opt not to renew their policies upon termination and, if the policyholder is unable to obtain other insurance, it is free either to proceed on a self-insured basis or to cease using the chemical in question. None of these conventional coverage scenarios poses an unavailability of insurance problem.

         Products such as asbestos and silica, however, present a different problem. For decades, insurers provided and policyholders obtained comprehensive general liability insurance under the mutual belief that those products could be produced and sold with relative safety.[32]By the time they discovered otherwise, and insurers concluded that they could no longer cost-effectively insure such risks, it was too late. Because the injuries involved were (1) long latency diseases that took decades to manifest, (2) not fully understood at the time of contracting, and (3) already so numerous and substantial by 1985 as to render them uninsurable, the parties faced a unique circumstance that was not anticipated or addressed in the policy language. See J. Stempel, supra, 12 Conn. Ins. L.J. 352-54.

         The question we must resolve, then, is who should bear the risk that a new type of long-tail injury will be discovered and that the insurance market will dry up midcourse, leaving a substantial backlog of dormant liability of which the policyholder and its prior insurers were both unaware at the time of contracting and for which a continuous chain of coverage will not be available. Courts and commentators have articulated four reasons why it is more efficient and reasonable for such risks to be borne by the insurers rather than the policy-holder.

         First, holding the insurers on the risk collectively responsible for the full injury, up to the policy limits for which the insured has contracted, has the desirable effect of maximizing the resources available to respond to the multitude of claims facing Vanderbilt and others similarly situated. See Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 472-73. Applying an unavailability rule also may encourage insurers who already are on the risk for long-tail injuries to continue to accept premiums-which presumably will go up as the risk becomes more apparent-and to make insurance available for a longer period of time, thereby spreading the risk among additional policies and generating additional resources to compensate victims of injury. See id. By contrast, a contrary rule that transfers liabilities to the policyholder as soon as insurance becomes unavailable would incentivize the insurance industry to stop offering coverage prematurely when novel risks emerge. The ensuing race to the exit would further reduce the resources available to respond to emerging risks. Cf. note, supra, 99 Harv. L. Rev. 1580.

         Second, holding insurers responsible when unforeseen risks arise, and not permitting them simply to drop coverage and cut their losses, creates an incentive for insurers as well as policyholders continuously to identify and investigate previously unknown risks associated with various materials and lines of business. Proponents of the unavailability rule have pointed to the public safety benefits that would result. See, e.g., M. Doherty, supra, 64 U. Chi. L. Rev. 266 and n.52, 285; J. Stempel, supra, 12 Conn. Ins. L.J. 468.

         Third, an unavailability of insurance rule best comports with the reasonable expectations of the insured. Insurance involves the transfer of risk. Doucette v. Pomes, 247 Conn. 442, 459, 724 A.2d 481 (1999). Absent contractual language to the contrary, a policyholder will reasonably expect that a comprehensive general liability policy will provide full coverage, up to the policy limits, not only for known risks but also for newly recognized long latency injuries. See Champion Dyeing & Finishing Co. v. Centennial Ins. Co., supra, 355 N.J.Super. 277; J. Stempel, supra, 12 Conn. Ins. L.J. 471-72. If a policyholder has been diligent in its efforts to maintain a continuous stream of coverage, then it may reasonably expect that it will be able to avail itself fully of such coverage in the event that unforeseen and ongoing injuries arise. Relatedly, to the extent that the relevant standard form policies are silent on the question, this ambiguity must be construed against the insurers that drafted the policy and in favor of the policyholder. See Wentland v. American Equity Ins. Co., 267 Conn. 592, 601, 840 A.2d 1158 (2004). This reflects the fact that insurers, who are in the business of managing risk, are better situated to anticipate such developments and, if they choose, draft policies that expressly address them. See J. Stempel, supra, 374-75, 382-83, 465.

         Fourth, our sister courts have noted that insurers have a better ability to manage this sort of risk. They can continue to accept, pool, and spread the risk, pricing coverage accordingly. See Owens-Illinois, Inc. v. United Ins. Co., supra, 138 N.J. 472-73. Or they can eschew the risk at whatever point it becomes unattractive to insure, at which time the policyholder is left with no choice but to effectively self-insure going forward. See J. Stempel, supra, 12 Conn. Ins. L.J. 465-68; see also Stonewall Ins. Co. v. Asbestos Claims Management Corp., supra, 73 F.3d 1204 (noting that insured cannot bargain around asbestos exclusions). The unavailability rule recognizes that the policyholder, unlike the insurer, has little if any ability to manage its exposure to dormant liabilities with respect to an emerging long-tail risk. For all of these reasons, we disagree with Boston Gas that, as a general proposition, it is unreasonable for insurers to bear the risk that the insurance industry will at some point cease to offer coverage for a particular long-tail risk, leaving a coverage gap for injuries already in progress.

         The court in Boston Gas also was concerned with what it identified as a more specific source of unfairness, namely, the situation in which only a few years of coverage are available to cover a substantial loss. See Boston Gas Co. v. Century Indemnity Co., supra, 454 Mass. 371. This might happen, for instance, if a hypothetical manufacturer entered the asbestos business in 1985 and purchased a comprehensive general liability policy from Insurer A for that year, after which time insurance became unavailable. Under those circumstances, Insurer A would have retained only one year worth of premiums, but it wouldbesolely responsible for defending and indemnifying decades of ensuing injuries sustained by all of the claimants who were exposed to the manufacturer's asbestos during that year.

         To reiterate what we already have said, the vast majority of our sister courts have concluded that, as a general matter, it is not unfair or unreasonable to allot to an insurer portions of an allocation block for which it did not write policies or receive premiums. If Insurer A insured a petroleum company for a single year during which that company was responsible for a catastrophic oil spill, Insurer A could be liable for years of ensuing cleanup costs, property damage, and other losses, despite having received only a single premium. See Champion Dyeing & Finishing Co. v. Centennial Ins. Co., supra, 355 N.J.Super. 276. It is not apparent, then, why the insurer should not also have to cover the full extent of injuries arising from asbestos exposures that occurred on its watch. Indeed, as we have discussed, many jurisdictions continue to adhere to the more policyholder-friendly all sums approach to long-tail allocation, according to which (1) the insured bears no responsibility for uninsured coverage blocks, and (2) any insurer on the risk can be called upon to bear the full costs of indemnifying and defending a long-tail tort claim, up to its policy limits. From this standpoint, it is difficult to see how the insurance industry, having received the benefits in Connecticut of a pro rata system, in which costs are uniformly allocated among policies and policyholders are responsible for uninsured periods, is treated unfairly in circumstances in which only one insurer happens to be on the risk. At worst, the liabilities of any particular insurer will be no greater than they would be in an all sums jurisdiction.

         We recognize that one consequence of the unavailability rule is that, in particular cases, individual insurers may end up bearing what appears to be a disproportionate share of the financial burden. But virtually every method of allocating long-tail tort liabilities will at times result in apparent inequities of one sort or another. Jurisdictions that apply an initial exposure trigger place a greater burden on insurers who provided coverage in the early years, whereas manifestation jurisdictions call on later insurers to carry more of the load. Courts that allocate costs by policy limits as well as by time on the risk[33] disadvantage issuers of larger policies, whereas any insurer on the risk may be singled out under the all sums approach. See J. Michaels et al., supra, 64 U. Kan. L. Rev. 477 (opining that all sums approach is inequitable). Ultimately, we believe that the allocation system that we have adopted and that our Supreme Court has at least implicitly endorsed- pro rata time-on-the-risk, employing a continuous trigger and an unavailability rule-distributes the burdens equitably among all parties involved and maximizes the resources available to respond to claims while minimizing administrative hassles and transaction costs.

         The second case on which Mt. McKinley relies is Sybron Transition Corp. v. Security Ins. of Hartford, supra, 258 F.3d 595, in which the United States Court of Appeals for the Seventh Circuit articulated a very different critique of the unavailability rule. In Sybron, Judge Frank Easterbrook, writing for the court, rejected the basic premise-accepted by most other courts to have considered the question-that it is possible for insurance against a particular risk ever to be ‘‘unavailable.'' Id., 599. Instead, he proceeded on the assumption that insurers will ‘‘cheerfully'' underwrite any risk at the right price. Id. This is true, Judge Easterbrook maintained, even when, as was arguably the case with asbestos in the mid-1980s, the ‘‘risk [already] has come to pass and the obligation to pay is certain, '' so that it is no longer possible for the insurer to spread the risk among different policyholders. Id. Under those circumstances, he explained, a would-be policyholder still can participate in insurance claim administration pools, although likely for apremium in excess of the maximum outlay. Id. The fact that an insured might have to pay more than $2 million to obtain a $2 million ‘‘retroactive'' asbestos policy, for example, reflects the fact that the underwriter, who actually would provide more of ‘‘a claims-administration service rather than risk-spreading . . . must be reimbursed for both the expected payments to victims and the expected costs of evaluating and resolving claims . . . .'' Id. Judge Easterbrook insisted that ‘‘[t]his kind of insurance could have been purchased for asbestos risks in the mid-1980s, '' and that a policyholder who opted not to join such a claims administration pool should, therefore, be treatedas self-insured. Id.

         There are two principal reasons-one factual and one legal-why we find the reasoning of Sybron to be unpersuasive in the context of this case. First, as a purely factual matter, there is nothing in the present record to support the assertion that, beginning in 1986, Vanderbilt could have joined the sort of insurance claim administration pool posited in Sybron. Quite the contrary; the trial court expressly found that insurance was not available to Vanderbilt or any similarly situated manufacturer. That finding was supported by substantial evidence, and Mt. McKinley does not challenge it on appeal.

         Second, from a legal standpoint, even if such a pool had been available to Vanderbilt, it would not have constituted the type of insurance that is relevant for purposes of the unavailability rule. As we previously have explained; see parts III A and III A 3 of this opinion; and as the court in Sybron acknowledged; Sybron Transition Corp. v. Security Ins. of Hartford, supra, 258 F.3d 601; we apply a continuous trigger, time-on-the-risk pro rata allocation system to long-tail asbestos claims in large part for epistemological reasons. Because asbestos related disease frequently follows repeated exposure to asbestos fibers, it often is impossible to know whether fibers inhaled at any particular time caused a particular disease, or what percentage of a claimant's injuries transpired in any given policy period. See id. When there is a continuous stream of coverage, then, the fairest and simplest approach is to divide the costs of defense and indemnity evenly among all of the policy periods during which injury may have occurred.

         This allocation scheme may theoretically present a moral hazard problem, however, as it might have been subject to abuse by a policyholder who attempted to avoid the cost of continuous coverage. Rather than purchase an excess policy every year, for example, an asbestos producer might have opted to acquire excess coverage only once every ten years, on the assumption that any asbestos related disease will take at least ten years to manifest and, therefore, at least one excess insurance policy will be available to respond to any long-tail claim. The producer could have obtained what would amount to full coverage at one-tenth of the cost. Aside from the fact that this outcome arguably would be unfair to the once-a-decade insurer, such a strategy would defeat the benefits of a continuous trigger approach; the risk-spreading function of insurance would be diminished and the resources available to respond to potential claims would be significantly reduced. See Security Ins. Co. of Hartford v. Lumbermens Mutual Casualty Co., supra, 264 Conn. 711. For these reasons, a court might have rightly treated the policyholder as self-insured under those circumstances.

         The situation is fundamentally different, however, when it becomes clear that virtually every company in a particular line of business faces a substantial backlog of dormant liability arising from its past activities, such that providing insurance to those companies will no longer perform a risk-spreading function and they are deemed to be uninsurable with respect to the risk at issue. Although Judge Easterbrook argues that they still can obtain insurance of a sort, he acknowledges; see Sybron Transition Corp. v. Security Ins. of Hartford, supra, 258 F.3d 599; that the claims administration pools that he describes are a fundamentally different creature, insofar as they do not advance what our Supreme Court has identified as the fundamental purpose of insurance, namely, to protect against the risk of loss. See Rathbun v. Health Net of the Northeast, Inc., 315 Conn. 674, 697, 110 A.3d 304 (2015); see also Doucette v. Pomes, supra, 247 Conn. 459 (‘‘transfer of risk . . . is generally considered to be an essential element of an insurance relationship''); Brown v. State Farm Fire & Casualty Co., 150 Conn.App. 405, 414, 90 A.3d 1054 (‘‘[a] loss that has already occurred is not fortuitous-and is thus not insurable''), cert. denied, 315 Conn. 901, 104 A.3d 106 (2014). Even if such pools had been available to Vanderbilt after 1985, then, they do not represent the sort of insurance that is germane to the unavailability rule. See Goodyear Canada, Inc. v. American International Cos., Docket No. CV-09-00377269, 2011 ONSC 5422, ¶¶ 57-65 (Can. Ont. Sup. Ct. J. September 16, 2011).

         We therefore conclude that the cases that have adopted an unavailability rule are better reasoned, represent the majority position, and more closely comport with our Supreme Court's analysis in Security. Accordingly, it was not improper for the trial court to exclude Vanderbilt from the allocation block for years in which asbestos related insurance was unavailable.

         2

         Equitable Exception and Testimony of Professor Priest

         In the alternative, Mt. McKinley contends that, if Connecticut does apply an unavailability of insurance rule, we should recognize an ‘‘equitable exception'' to that rule. Under the proposed equitable exception, costs would be prorated to the insured if the insured continues to place allegedly harmful products into the stream of commerce during a time when no coverage is available for losses attributed to those products. Under those circumstances, Mt. McKinley argues, the insured assumes any risk resulting from the ongoing production, sale, or installation of a product that is recognized to be so harmful as to be uninsurable. Although the question may be a close one, we conclude that the trial court properly declined Mt. McKinley's invitation to apply an equitable exception under the circumstances of the present case. We also conclude that the trial court did not abuse its discretion in precluding expert testimony on the issue.

         The following additional procedural history is relevant to our analysis of these issues. During the Phase II trial, Mt. McKinley argued that, if the trial court applied an unavailability of insurance rule, the court also should apply anequitable exception and treat Vanderbilt as self-insured for the period from March 3, 1986, through 2008, during which Vanderbilt continued to sell talc while uninsured or underinsured. In light of the ‘‘considerable credible evidence'' that Vanderbilt made a business decision to continue selling talc beyond 1986 even though it was aware of the potential legal exposure, the trial court opined that ‘‘Mt. McKinley's equitable argument possesses appeal.'' Nevertheless, the court declined to apply an equitable exception for three reasons. First, after reviewing the relevant case law, the court concluded that there was no authority for considering Vanderbilt's post-1985 conduct when determining whether costs should be prorated to it for that period. Second, the court reasoned that Vanderbilt's pre-1986 insurers were contractually bound to provide coverage for injuries arising from exposures prior to 1986, and that nothing in the policy language or the insurers' course of dealing with Vanderbilt indicated that that coverage would be nullified if Vanderbilt continued to sell talc after 1986. Third, the court found that, even if it were free as a matter of law to apply an equitable exception, the equities of the case did not support it. Specifically, the court found that (1) Vanderbilt consistently took the position both before and after 1985 that its talc did not contain asbestos; (2) there was no evidence in the record demonstrating that talc does contain asbestos; (3) the federal government in 1992 reinforced Vanderbilt's position in this regard by excluding talc from regulation under the Occupational Safety and Health Administration's new asbestos ...


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