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HAZMAT Gas Classification

Hazardous materials, otherwise known as Hazmat, consist of solids, liquids or gases that pose a direct or indirect threat to people, animals, property, environment or organisms. These materials can include goods that are radioactive, flammable, explosive, corrosive, toxic, biohazardous or even allergenic. The U.S. Department of Transportation has classified gases, among other materials, into three divisions, all under Class 2 of the nine-class hazardous materials system.

  1. Flammable Gas

    • Flammable gas is classified as the first division in Class 2 of the Department of Transportation. Division 2.1, flammable gas, is defined as a gas at 20 degrees Celsius or below and 101.3 ambient temperature and pressure (kPa). The gas will have a boiling point of 20 degrees Celsius at sea level. Additional criteria for this division include gases that are ignitable when mixed by volume with 13 percent or less with air, or have a flammability range of at least 12 percent. Gases in this category include acetylene and hydrogen.

    Non-Flammable Gas/Non-Poisonous Compressed Gas

    • Non-flammable and non-poisonous compressed gas is classified in the second division of Class 2 by the Department of Transportation. Division 2.2, non-flammable and non-poisonous compressed gas, is defined as a material or mixture that exerts an absolute pressure of 280 kPa, or 40.6 psi, or higher at 20 degrees Celsius. Gases classified in this division do not meet the criteria for gasses in Division 2.1 or 2.3. This division includes compressed gas, pressurized cryogenic gas, compressed gas in a solution, liquefied gas,asphyxiant gas and oxidizing gas. Gases in this category include nitrogen and neon.

    Poisonous Gas

    • Gases that are poisonous by inhalation are classified in the third division of Class 2 by the Department of Transportation. Gases in this division are a gas at 20 degrees Celsius or below and 101.3 kPa of pressure. Division 2.3 gases will have a boiling point of 20 degrees Celsius at sea level. They may also be toxic and pose a hazard during transportation. These gases have the ability to cause death or serious injury if inhaled. Gases in this category include fluoride, chlorine and hydrogen cyanide.

    Other Classes

    • The Department of Transportation classifies all hazardous materials, not just gases. Their class system starts at Class 1, which includes explosives. Explosives are further categorized according to compatibility with other explosives. Class 3 consists of flammable liquid and is further classified by combustibility. Class 4 consists of flammable solids and is further classified by flammability, ability to spontaneously combust, and danger when solid is wet. Class 5 consists of oxidizing agents and organic peroxides. Class 6 includes toxic and infectious substances. Class 7 consists of radioactive substances, Class 8 of corrosive substances, and Class 9 is for miscellaneous substances that do not fit the requirements of another class.

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