Duane L. KNOPIK, Plaintiff-Appellant, v. BP PRODUCTS NORTH AMERICA, INC., Defendant-Appellee, and Exxonmobil Oil Corporation, Defendant-Cross Appellant, and Enecotech Midwest Inc., Defendant-Appellee, and Conocophillips Company, Sinclair Oil Corporation, Unocal Corporation, Leggette, Brashears & Graham, Inc., Dpra Incorporated, and Braun Intertec Corporation, Defendants; Duane L. Knopik, Plaintiff-Appellee, v. BP Products North America, Inc., Defendant-Appellant, and Exxonmobil Oil Corporation, Defendant-Cross Appellee, and Braun Intertec Corporation, Defendant-Appellee, and Enecotech Midwest Inc., Defendant-Appellee, and Conocophillips Company, Sinclair Oil Corporation, Unocal Corporation, Leggette, Brashears & Graham, Inc., and Dpra Incorporated, Defendants