Compressed Natural Gas (CNG) 1 : A natural lighter-than-air gas compressed for use as a fuel that consists principally of methane in gaseous form plus naturally occurring mixtures of hydrocarbon gases
NFPA 302 Fire Protection Standard for Pleasure and Commercial Motor Craft, 1998 ed. https://www.nfpa.org/assets/files/AboutTheCodes/30 2/302-A2003-rop.PDF, (Std: Fr Prac for Pleasure and Comm Motor Craft - Amer) {292 NFC}