DOT Hazard Class

Class 2.1

Flammable Gas

49 CFR §173.115(a)

Placard: Red placard with flame symbol

ERG entries

161

Divisions

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Packing groups

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Compat groups

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Definition

A gas that at 20 °C (68 °F) and standard atmospheric pressure (101.3 kPa) is ignitable when in a mixture of 13% or less by volume with air, OR has a flammable range with air of at least 12 percentage points regardless of the lower flammable limit.

Primary hazards

Extremely flammable — will be easily ignited by heat, sparks, or flames
Vapors may travel to source of ignition and flash back
Cylinders exposed to fire may BLEVE (Boiling Liquid Expanding Vapor Explosion)
Vapors are heavier than air and may accumulate in low areas or confined spaces

Public safety response

Isolate spill or leak area for at least 100 m (330 ft) in all directions. Stay upwind. Keep out of low areas. Ventilate closed spaces before entering.

Common materials in this class

Propane, butane, LPG, natural gas (CNG/LNG), acetylene, hydrogen, ethylene, aerosols (flammable).

UN1011Butane UN1075Petroleum gases, liquefied (LPG)UN1075Propane UN1971Natural gas, compressed UN1001Acetylene, dissolved

Special provisions / notes

Cargo tank motor vehicles carrying liquefied compressed flammable gases require BLEVE-aware response — see the BLEVE Safe Distances table (ERG 2024 p. 359).