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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:

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

Questions? Visit the EH&S Chemical Hygiene website or call Chemical Hygiene Officer, (951) 827-5528.