Section 162.028-2 - Classification(a) Portable and semi-portable extinguishers must be marked with a combined number and letter designation. The letter designates the general class of fire for which the extinguisher is suitable as identified in NFPA 10 (incorporated by reference, see § 162.028-1 ). The number indicates the relative extinguishing potential of the device as rated by UL 711 (incorporated by reference, see § 162.028-1 ).CGFR 60-36, 25 FR 10640, Nov. 5, 1960, as amended by USCG-2012-0196, 81 FR 48278, July 22, 2016