The Supreme Court of Pennsylvania adopted the "multiple trigger" theory for liability and held that each insurer that provided coverage during the triggering periods was jointly and severally liable for the entire loss.
J.H. France Refractories Co. v. Allstate Insurance Co., 626 A.2d 502 (Pa. 1993).
Martin L. Ryan,
Insurance Law - Indemnification - Multiple Insurers - Asbestos Claims,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol32/iss3/12