BALTIMORE - While two insurance companies are correct that Maryland follows the horizontal exhaustion rule for determining primary and excess policy coverage, the rule must be applied based on the theory of pro-rata allocation, as a former insulation company seeking coverage for asbestos personal injury claims argued, a Maryland federal judge held Jan. 2 in granting the insurers and the company summary judgment in part (National Union Fire Insurance Company of Pittsburgh, Pa., et al. v. Porter Hayden Co., No. 03-3408, D. Md.; 2014 U.S. Dist. LEXIS 114).