UN/NA Number Reference
DOT Class 2.1 Flammable Gas placard

UN 1966: Hydrogen, refrigerated liquid

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 1966 is assigned the proper shipping name Hydrogen, refrigerated liquid in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 2.1 Flammable Gas material. Required label(s): 2.1.

Packing group indicates the degree of danger within a hazard class: PG I is high danger, PG II medium, PG III low. The proper shipping name, hazard class, UN number, and packing group together form the basic shipping description that must appear on shipping papers and, where required, on the package and placard.

Emergency Response (ERG Guide 115)

Hazards: Extremely flammable. May be ignited by heat, sparks, or flames. Vapors may travel to ignition source and flash back. Containers may rocket or BLEVE.

Fire: Do not extinguish unless flow can be stopped. Use water spray to cool containers. Move containers from fire if safe.

Spill: Eliminate ignition sources. Stop leak if safe. Use water spray to reduce vapors.

Chemical and Physical Properties

Hydrogen is a colorless, odorless gas. It is easily ignited. Once ignited it burns with a pale blue, almost invisible flame. The vapors are lighter than air. It is flammable over a wide range of vapor/air concentrations. Hydrogen is not toxic but is a simple asphyxiate by the displacement of oxygen in the air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. Hydrogen is used to make other chemicals and in oxyhydrogen welding and cutting.

CAS Number: 1333-74-0
Molecular Formula: H2
Molecular Weight: 2.016 g/mol
Color / Form: Colorless gas
Odor: Odorless
Boiling Point: -423 °F
Melting Point: -434 °F (USCG, 1999)
Flash Point: Flammable gas
Autoignition: 1065 °F (USCG, 1999)
Specific Gravity: 0.071 (floats on water)
Vapor Pressure: 1.24X10+6 mm Hg at 25 °C
Vapor Density: Relative vapor density (air = 1): 0.07
Water Solubility: In water, 1.62 mg/L at 21 °C

Special Provisions

49 CFR 172.102 special provision codes for this entry: T75, TP5. These codes modify the general requirements (packaging, quantity limits, exceptions) for this specific material. Look up each code in 49 CFR 172.102 for the full text.

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Reference data compiled from the DOT Hazardous Materials Table (49 CFR 172.101), the 2024 Emergency Response Guidebook, and public chemical databases (PubChem, NIOSH, EPA). Always verify the correct shipping description against the current regulation and the manufacturer's SDS Section 14 before shipping.