HAZMAT Class 2 Gases

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The HAZMAT Class 2 in United States law includes all gases which are compressed and stored for transportation. Class 2 has three divisions: Flammable (also called combustible), Non-Flammable/Non-Poisonous, and Poisonous. This classification is based on the United Nations' Recommendations on the Transport of Dangerous Goods - Model Regulations. In Canada, the Transportation of Dangerous Goods Regulations, or TDGR, are also based on the UN Model Regulations and contain the same three divisions.


A propane tank car after a fire, the HAZMAT 1075 symbol can be seen in red as a warning of the danger posed by the gas.

A gas is a substance which

  1. (a) at 50 °C (122 °F) has a vapor pressure greater than 300 kPa or
  2. (b) is completely gaseous at 20 °C (68 °F) at a standard pressure of 101.3 kPa
  1. Gases assigned to one of three divisions
  1. division 2.1 Flammable gas
  2. division 2.2 Non flammable, Non-toxic gas
  3. division 2.3 Toxic gas
Loading a container (with the Hazmat Class 2 symbol on the rear doors) aboard a ship.

Division 2.2: Non-Flammable, Non-Toxic Gas

This division includes compressed gas, liquefied gas, pressurized cryogenic gas, compressed gas in solution, asphyxiant gas and oxidizing gas. A non-flammable, nonpoisonous compressed gas (Division 2.2) means any material (or mixture) which:

  1. Exerts in the packaging an absolute pressure of 280 kPa (40.6 psia) or greater at 20 °C (68 °F), and
  2. Does not meet the definition of Division 2.1 or 2.3.

Division 2.3: Toxic Gas

Gas poisonous by inhalation means a material which is a gas at 20 °C or less and a pressure of 101.3 kPa (a material which has a boiling point of 20 °C or less at 101.3kPa (14.7 psi)) and which:

  1. Is known to be so toxic to humans as to pose a hazard to health during transportation, or
  2. In the absence of adequate data on human toxicity, is presumed to be toxic to humans because when tested on laboratory animals it has an LC50 value of not more than 5000 ml/m³. See 49CFR 173.116(a) for assignment of Hazard Zones A, B, C or D. LC50 values for mixtures may be determined using the formula in 49 CFR 173.133(b)(1)(i)


Class 2.1: Flammable Gas Hazardous Materials
Class 2.1: Flammable Gas
Class 2.2: Nonflammable Gas Hazardous Materials
Class 2.2: Nonflammable Gas
Class 2.2: Oxygen (Alternative Placard) Hazardous Materials
Class 2.2: Oxygen (Alternative Placard)
Class 2.3: Inhalation Hazard (Alternative Placard) Hazardous Materials
Class 2.3: Inhalation Hazard (Alternative Placard)

Compatibility table[edit]

Load and Segregation Chart
  Weight 1.1 1.2 1.3 1.4 1.5 1.6 2.1 2.2 2.2 2.3 3 4.1 4.2 4.3 5.1 5.2 6.1 7 8
2.1 1001 lb X X X O X         X O             O O  
2.2 1001 lb B X       X         X O                  
2.2 1001 lb B X       X         X O                  
2.3A any qty X X X O X   X         X X X X X X     X
2.3B any qty X X X O X   O         O O O O O O      
The absence of any hazard class or division or a blank space in the table indicates that no restrictions apply.
  • *: This indicates that segregation among different Class 1 materials is governed by the compatibility table in 49CFR 177.848(f)
  • X: These materials may not be loaded, transported, or stored together in the same transport vehicle or storage facility during the course of transportation.
  • O: Indicates that these materials may not be loaded, transported or stored together in the same transport vehicle or storage facility during the course of transportation, unless separated in a manner that, in the event of leakage from packages under conditions normally incident to transportation, commingling of hazardous materials would not occur.
  • A: This note means that, notwithstanding the requirements of the letter 'X', ammonium nitrate fertilizer may be loaded or stored with Division 1.1 or Division 1.5 materials.


  • United Nations, Recommendations on the Transport of Dangerous Goods - Model Regulations
  • 49 CFR 173.115 (a) (U.S. Code)
  • 49 CFR 173.115 (b) (U.S. Code)
  • 49 CFR 177.848 (U.S. Code)