On May 1, 2015, the United States Court of Appeals for the DC Circuit vacated US Environmental Protection Agency's (EPA) emission standard exemptions for emergency reciprocating internal combustion engines that operate up to 100 hours a year for “emergency demand response.” Delaware Dep’t of Nat. Resources & Envtl. Control v. EPA, No. 13-1093 (May 1, 2015). The exemption allowed emergency backup generators to operate 100 hours a year when either a Level 2 Energy Emergency Alert is declared or there is a 5% drop in voltage or frequency below standard levels.