Single incident product liability claims. Single incident product liability claims involve incidents of short duration that are typically known when they occur and involve observable injuries, which provide an objective basis for quantifying damages. The Company estimates its liability for asserted single incident product liability claims based on expected settlement costs for asserted single incident product liability claims. The estimate for incurred but not reported ("IBNR") single incident product liability claims is based on experience, sales volumes, and other relevant information. The reserve for single incident product liability claims, which includes asserted single incident product liability claims and IBNR single incident product liability claims, was $1.5 million and $1.4 million at June 30, 2021 and December 31, 2020, respectively. Single incident product liability expense was $0.1 million during the six months ended June 30, 2021 and $0.3 million during the six months ended June 30, 2020. Single incident product liability exposures are evaluated on an annual basis, or more frequently if changing circumstances warrant. Adjustments are made to the reserve as appropriate.

Cumulative trauma product liability claims. Cumulative trauma product liability claims involve alleged exposures to harmful substances (e.g., silica, asbestos and coal dust) that occurred years ago and may have developed over long periods of time into diseases such as silicosis, asbestosis, mesothelioma, or coal worker’s pneumoconiosis. One of the Company's affiliates, Mine Safety Appliances Company, LLC ("MSA LLC"), was named as a defendant in 1,610 lawsuits comprised of 3,942 claims as of June 30, 2021. These lawsuits mainly involve respiratory protection products allegedly manufactured and sold by MSA LLC or its predecessors. The product models alleged were manufactured many years ago by MSA LLC and are no longer sold.

The increases in the number of claims in 2020 and in 2021, are largely attributable to an increase in claims alleging injuries from exposure to coal mine dust including plaintiffs' counsels with which MSA LLC does not have substantial prior experience, alleging product models that were manufactured many years ago by MSA LLC and are no longer sold.

Total cumulative trauma product liability reserve was $226.1 million at June 30, 2021, including $11.0 million for claims settled but not yet paid and related defense costs, and $221.5 million at December 31, 2020, including $7.8 million for claims settled but not yet paid and related defense costs. This reserve includes estimated amounts for asserted claims and IBNR claims. Those estimated amounts reflect asbestos, silica and coal dust claims expected to be resolved through the year 2069 and are not discounted to present value. The Company revised its estimates of MSA LLC's potential liability for cumulative trauma product liability claims for the year ended December 31, 2020 as a result of its annual review process described below. The reserve was also increased during the second quarter of 2021 to reflect an increase in the number of asserted claims pending against MSA LLC. The Company is monitoring developments in filing rates to determine the potential for impact on long-term filing trends. The reserve does not include amounts which will be spent to defend the claims covered by the reserve. Defense costs are recognized in the unaudited Condensed Consolidated Statement of Income as incurred.

At June 30, 2021, $35.0 million of the total reserve for cumulative trauma product liability claims is recorded in the Insurance and product liability line within other current liabilities in the unaudited Condensed Consolidated Balance Sheet and the remainder, $191.1 million, is recorded in the Product liability and other noncurrent liabilities line. At December 31, 2020, $35.3 million of the total reserve for cumulative trauma product liability claims is recorded in the Insurance and product liability line within other current liabilities in the unaudited Condensed Consolidated Balance Sheet and the remainder, $186.2 million, is recorded in the Product liability and other noncurrent liabilities line.

Total cumulative trauma liability losses were $24.5 million and $27.5 million for the three and six months ended June 30, 2021 and related to an update to our asserted cumulative trauma product liability reserve as well as the defense of cumulative trauma product liability claims. Total cumulative trauma liability losses were $1.2 million and $3.3 million for the three and six months ended June 30, 2020 primarily related to the defense of cumulative trauma product liability claims. Uninsured cumulative trauma product liability losses, which were included in Product liability expense on the unaudited Condensed Consolidated Statements of Income, were $11.8 million and $14.5 million for the three and six months ended June 30, 2021 and $0.9 million and $2.8 million for the three and six months ended June 30, 2020, respectively, and represent the total cumulative trauma liability losses net of any estimated insurance receivables as discussed below.

To develop a reasonable estimate of MSA LLC’s potential exposure to cumulative trauma product liability claims, Management performs an annual review of MSA LLC’s cumulative trauma product liability claims in consultation with an outside valuation consultant and outside legal counsel. The review process takes into account developments in MSA LLC’s claims experience over the past year, developments in the tort system generally, and any other relevant information. Quarterly, management and outside legal counsel review whether significant new developments have occurred which could materially impact recorded amounts for asserted claims, and if warranted management reviews changes with an outside valuation consultant.

Cumulative trauma product liability litigation is inherently unpredictable and MSA LLC's expense with respect to cumulative trauma product liability claims could vary significantly in future periods. It is difficult to reasonably estimate how many claims will be newly asserted against MSA LLC in any given period or over the lifetime of MSA LLC's claims experience. Case solicitation and filing activity, in our experience, is unique to each plaintiffs’ counsel and also influenced by external factors. Once asserted it is unclear at the time of filing whether a claim will be actively litigated, or the extent of ultimate loss, if any, in the absence of discovery at initial case stages. Even when a case is actively litigated, it is often difficult to determine if the lawsuit will be dismissed without payment or settled, because of sufficiency of product identification, statute of limitations challenges, or other defenses. This difficulty is increased when claims are asserted by plaintiffs’ counsel with which MSA LLC does not have substantial prior experience, as claims experience can vary significantly among different plaintiffs' counsel. As a result of all of these factors, it is typically unclear until late into litigation whether any particular claim, or inventories of claims, will result in losses and, if so, to what extent. Actual loss amounts for settled claims are highly variable and turn on a case-by-case analysis of the relevant facts. As more information is learned about asserted claims, adjustments may be made to the cumulative trauma product liability reserve as appropriate.

With respect to asserted or IBNR claims, MSA LLC’s expense in future periods may vary from the reserve currently established for several reasons. In particular, MSA LLC’s actual claims experience may differ in one or more respects from the significant assumptions listed above that were used by in establishing the reserve. Factors that make MSA LLC's asserted and IBNR claims difficult to reasonably estimate include uncertainty as to the number of claims that may be asserted in the future (and over what time periods), the wide variability in the alleged severity of claims asserted, changes in the severity of claims over time, and the number of claims that ultimately will be resolved with payment. This difficulty is increased when claims are asserted by plaintiffs' counsel, with which MSA LLC does not have substantial prior experience (as claims experience can vary significantly among different plaintiffs' counsel), the historically low volume of claims asserted and resolved, and numerous other factors. Numerous uncertainties also exist with respect to factors not specific to MSA LLC, including potential legislative or judicial changes at the federal level or in key states concerning claims adjudication, future bankruptcy proceedings involving key co-defendants, payments from trusts established to compensate claimants, and/or changes in medical science relating to the diagnosis and treatment of claims.

Because cumulative trauma product liability litigation is subject to the significant modeling assumptions and inherent uncertainties described above, and unfavorable developments or rulings could occur, there can be no certainty that MSA LLC may not ultimately incur charges in excess of presently recorded liabilities. The reserve for cumulative trauma product liability claims may be adjusted from time to time based on changes to the factors and assumptions described above. If future estimates of cumulative trauma product liability claims are materially different than the accrued liability, we will record an appropriate adjustment to the unaudited Condensed Consolidated Statement of Income. These adjustments could materially impact our consolidated financial statements in future periods.

Many years ago, MSA LLC purchased insurance policies from various insurance carriers that, subject to common contract exclusions, provided coverage for cumulative trauma product liability losses (the "Occurrence-Based Policies"). While we continue to pursue reimbursement under certain remaining Occurrence-Based Policies, the vast majority of these policies have been exhausted, settled or converted into either (1) negotiated settlement agreements with scheduled payment streams (recorded as notes receivables), or (2) negotiated Coverage-in-Place Agreements (recorded as insurance receivables). As a result, MSA LLC is largely self-insured for cumulative trauma product liability claims, and additional amounts recorded as insurance receivables or notes receivables will be limited.

When adjustments are made to amounts recorded in the cumulative trauma product liability reserve, we calculate amounts due to be reimbursed pursuant to the terms of the negotiated Coverage-In-Place Agreements, including cumulative trauma product liability losses and related defense costs, and we record the amounts probable of reimbursement as insurance receivables. These amounts are not subject to current coverage litigation.

Insurance receivables at June 30, 2021 totaled $104.1 million of which, $12.9 million is reported in Prepaid expenses and other current assets in the unaudited Condensed Consolidated Balance Sheet and $91.2 million is reported in Insurance receivable and other noncurrent assets. Insurance receivables at December 31, 2020 totaled $97.0 million, of which $12.0 million was reported in Prepaid expenses and other current assets in the unaudited Condensed Consolidated Balance Sheet and $85.0 million was reported in Insurance receivable and other noncurrent assets. The vast majority of the $104.1 million insurance receivables balance at June 30, 2021 is attributable to reimbursement believed to be due under the terms of signed Coverage-In-Place Agreements and a portion of this amount represents the estimated recovery of IBNR amounts not yet incurred.

Notes receivable from insurance companies at June 30, 2021, totaled $53.0 million, of which $3.9 million is reported in Notes receivable, insurance companies, current on the unaudited Condensed Consolidated Balance Sheet and $49.1 million is reported in Notes receivable, insurance companies, noncurrent. Notes receivable from insurance companies at December 31, 2020 totaled $52.3 million of which $3.8 million was reported in Notes receivable, insurance companies, current on the unaudited Condensed Consolidated Balance Sheet and $48.5 million was reported in Notes receivable, insurance companies, noncurrent.

The vast majority of the insurance receivables balance at June 30, 2021, is attributable to reimbursement under the terms of signed agreements with insurers and is not currently subject to litigation. The collectibility of MSA LLC's insurance receivables and notes receivables is regularly evaluated and we believe that the amounts recorded are probable of collection. The determination that the recorded insurance receivables are probable of collection is based on the terms of the settlement agreements reached with the insurers, our history of collection, and the advice of MSA LLC's outside legal counsel and consultants. Various factors could affect the timing and amount of recovery of the insurance and notes receivables, including assumptions regarding various aspects of the composition and characteristics of future claims (which are relevant to calculating reimbursement under the terms of certain Coverage-In-Place Agreements) and the extent to which the issuing insurers may become insolvent in the future.

The Company provides warranties on certain product sales. Product warranty reserves are established in the same period that revenue from the sale of the related products is recognized, or in the period that a specific issue arises as to the functionality of the Company's product. The determination of such reserves requires the Company to make estimates of product return rates and expected costs to repair or to replace the products under warranty.

The amounts of the reserves are based on established terms and the Company's best estimate of the amounts necessary to settle future and existing claims on products sold as of the balance sheet date. If actual return rates and/or repair and replacement costs differ significantly from estimates, adjustments to recognize additional cost of sales may be required in future periods.