Environmental Health & Safety

Toxic and Hazardous Gas Classifications

Learn the hazard class of toxic and hazardous gases.

Find everything you wanted to know about compressed gases including hazard class, description and hazards, regulatory information, signs and symptoms of exposure, and more on the Toxic and Hazardous Gas Classifications Chart below or download the entire Toxic and Hazardous Gas Classification Chart (PDF). Always follow Hazard Class Requirements and Safety Requirements for your material, based on hazard class.

Definition: Liquefied gas

Liquefied gas means a gas which when packaged under pressure, is partially liquid at temperatures above-50°C. A distinction is made between:

(i) High pressure liquefied gas: a gas with a
critical temperature between -50°C and+65°C; and

(ii) Low pressure liquefied gas: a gas with a
critical temperature above +65°C.

Compressed Gas Safety Level (CGSL) defined as ppm:

• Class I = < 200 LC50
• Class II = 201–2000 LC50
• Class III >= 2001–5000 LC50
• Class IV >= 5000

Class as defined in 2020 Fire Code:

• Highly toxic = < 200 LC50
• Toxic = 201–2000 LC50

Table references and resources:

• 2020 California Fire Code
• Immediately Dangerous to Life or Health Concentrations (IDLHs), published in 1994, National Institute for Occupational Safety and Health (NIOSH)
• Registry of Toxic Effects of Chemical Substances, Canadian Centre for Occupational Health & Safety
• Table AC-1 Permissible Exposure Limits for Chemical Contaminants, California Department of Industrial Relations, Title 8, Section 5155
• Threshold Limit Values (TLV) and Immediately Dangerous to Life and Health (IDLH) Values (PDF), Matheson Tri-Gas

Important: This chart is intended for use by employees only. Standards and requirements may differ at other institutions and businesses.