Gases : Critical temperature is the A substance which has a critical temperature below 50°C, has a vapour temperature above which pressure of more than 3 bars absolute (highly volatile) is classified as a gas.

Different types of gases and their hazards have been explained with examples. Gases are divided into 3 subclasses on the basis of their hazardous nature.

i) Flammable gases e.g. acetylene, liquefied petroleum gas (LPG)

ii) Toxic gases e.g. chlorine, sulphur dioxide

iii) Non flammable nontoxic gases e.g. carbon dioxide, nitrogen, etc.