The EPA also exempted flammable mixtures including blendstocks117 and natural gasoline that do not meet the NFPA flammability rating of 4.118 However, flammable mixtures and blendstocks meeting the NFPA 4 flammability are subject to threshold determinations119 irrespective of their end use. If a mixture consists of 1% or greater concentration of a regulated flammable substance and the mixture meets the NFPA 4 flammability criteria, the EPA considers the entire weight of a flammable mixture as the regulated flammable substance.120 The EPA recognizes specific circumstances in which a facility not covered under the List Rule has the potential for a vapor cloud explosion, and it asserts that the General Duty Clause protects against site-specific factors that “make an unlisted chemical extremely hazardous.”121