The Hazard Characteristic Code (HCC) designation for Gas, Poison, Flammable. Hazard Group & Comments: Any product which is required to be shipped as a UN Class 2.3 under 49 CFR 173.115(c) (Gas, poisonous by inhalation), is required to be marked "Inhalation Hazard" under 49 CFR 172.313, and meets the definition of a Flammable Gas (HCC G2)