# 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 LC$_{50}$ value of not more than 5000 ml/m$^3$. See 49CFR 173.116(a) for assignment of Hazard Zones A, B, C or D. LC$_{50}$ values for mixtures may be determined using the formula in 49 CFR 173.133(b)(1)(i)

## Placards

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

## Compatibility table

Load and Segregation Chart :
| | Weight | Weight | 1.1 | 1.2 | 1.3 | 1.4 | 1.5 | 1.6 | 2.1 | 2.2 | 2.2 | 2.3 | 2.3 | 3 | 4.1 | 4.2 | 4.3 | 5.1 | 5.2 | 6.1 | 7 | 8 |
| | Weight | Weight | 1.1 | 1.2 | 1.3 | 1.4 | 1.5 | 1.6 | 2.1 | 2.2 | 2.2 | A | B | 3 | 4.1 | 4.2 | 4.3 | 5.1 | 5.2 | A | 7 | 8 |
| 2.1 | 1,001 lb (454 kg) | 1,001 lb (454 kg) | | | | O | | | | | | | O | | | | | | | O | O | |
| 2.2 | 1,001 lb (454 kg) | B | | | | | | | | | | | O | | | | | | | | | |
| 2.2 | 1,001 lb (454 kg) | B | | | | | | | | | | | O | | | | | | | | | |
| 2.3A | Any Quantity | Any Quantity | | | | O | | | | | | | | | | | | | | | | |
| 2.3B | Any Quantity | Any Quantity | | | | O | | | O | | | | | O | O | O | O | O | O | | | |
| Key |||||||||||||||||||||||
| The absence of any hazard class or division or a blank space in the table indicates that no restrictions apply. 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. B: For domestic shipments of compressed oxygen, or refrigerated liquid oxygen the "Oxygen" placard may be used instead of a "Non-flammable Gas" placard. See §172.504(f)(7). Source: United States Code of Federal Regulations, Title 49 CFR §177.848 - Segregation of hazardous materials. |||||||||||||||||||||||