HAZMAT Class 2 Gases

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.

Divisions

A gas is a substance which
#(a) at 50 °C (122 °F) has a vapor pressure greater than 300 kPa (43.51 PSI) or
#(b) is completely gaseous at 20 °C (68 °F) at a standard pressure of 101.3 kPa (14.69 PSI).

Gases are assigned to one of three divisions

#division 2.1 Flammable gas
#division 2.2 Non flammable, Non-toxic gas
#division 2.3 Toxic gas

Aerosols also fall into Class 2 divisions where an aerosol is defined as an article consisting of any non-refillable receptacle containing a gas compressed, liquefied or dissolved under pressure, the sole purpose of which is to expel a nonpoisonous (other than a Division 6.1 Packing Group III material) liquid, paste, or powder and fitted with a self-closing release device allowing the contents to be ejected by the gas.

Division 2.1: Flammable, Non-Toxic Gas

Flammable gas means any material that:
#Is ignitable at 101.3 kPA (14.7 psia) when in a mixture of 13 percent or less by volume with air; or
#Has a flammable range at 101.3 kPa with air of at least 12 percent regardless of the lower limit.
#Is determined to be flammable in accordance with ASTM E681-85, Standard Test Method for Concentration Limits of Flammability of Chemicals

The following applies to aerosols:
#An aerosol must be assigned to Division 2.1 if the contents include 85% by mass or more flammable components and the chemical heat of combustion is 30 kJ/g or more;
#An aerosol must be assigned to Division 2.1 if it is deemed flammable in accordance with the appropriate tests of the UN Manual of Tests and Criteria for flammability.

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:

A non-flammable gas means any material that:
#Exerts in the packaging an absolute pressure of 280 kPa (40.6 psia) or greater at 20 °C (68 °F), and
#Does not meet the definition of Division 2.1 or 2.3.

The following applies to aerosols:
#An aerosol must be assigned to Division 2.2 if the contents contain 1% by mass or less flammable components and the heat of combustion is less than 20 kJ/g.

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:

#Is known to be so toxic to humans as to pose a hazard to health during transportation, or
#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)

Placards

Compatibility table

References

*
*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)

{{Hazardous materials

Gases