Natural gas
Natural gas means a naturally occurring mixture of hydrocarbon and non-hydrocarbon gases found in geologic formations beneath the Earth's surface, of which the principal constituent is methane. May be field or pipeline quality. For the purposes of this subpart, the definition of natural gas includes similarly constituted fuels such as field gas, refinery gas, and syngas.
Source
40 CFR § 63.6175
Scoping language
Terms used in this subpart are defined in the CAA; in 40 CFR 63.2, the General Provisions of this part; and in this section: