Hazard Class 2

Class 2 - Gases is divided into the following three divisions:

• Division 2.1 - Flammable gas
• Division 2.2 - Non-flammable, non-poisonous, compressed gas
• Division 2.3 - Poisonous gas

There are four physical states of gas, described as follows when packaged under pressure for transport:

• Compressed gas is entirely gaseous at -50° C (-58° F). This includes all gases with a critical temperature less than or equal to -50° C (-58° F).
• Liquefied gas is partially liquid at temperatures above -50° C (-58° F). High-pressure liquefied gases have a critical temperature between -50° C (-58° F) and +65° C (149° F). Low-pressure liquefied gases have a critical temperature above +65° C (149° F).
• Refrigerated liquefied gas is made partially liquid because of its low temperature. This is also referred to as cryogenic liquid.
• Dissolved gas is dissolved in a liquid phase solvent.

Class 2 includes compressed gases, liquefied gases, dissolved gases, refrigerated liquefied gases, mixtures of one or more gases, and aerosols. Class 2 materials are covered in §173.115.

Division 2.1 - Flammable gas includes any gas which, when mixed with air in certain proportions, forms a flammable mixture. Examples of flammable gas include butane, hydrogen, and propane.

Division 2.2 - Non-flammable, non-poisonous, compressed gas includes all non-flammable, non-toxic gases, or low temperature liquefied gases. These gases may be asphyxiation or oxidizing hazards. Gases that are asphyxiants dilute or replace the amount of oxygen in the atmosphere and cause suffocation. Oxidizing gases may cause or contribute to combustion of other materials. Examples include carbon dioxide, neon, and liquefied nitrogen or helium.

Division 2.3 - Poisonous gas includes gases known or presumed to be so toxic to humans as to pose a hazard to health during transportation. They have an LC₅₀ value equal to or less than 5,000 mL/m³ (ppm). Examples of these gases include chlorine and cyanide.

To learn more about DOT HAZMAT Awareness visit our DOT HAZMAT General Awareness Online Training web page.