HC Deb 03 June 1938 vol 336 c2426W
Mr. C. Wilson

asked the Home Secretary whether he can explain the terms true gas, persistent gas and contaminating gas, and give a list of each?

Mr. Lloyd:

The term "gas" in warfare means any chemical substance, whether solid, liquid or vapour, which is used because it produces poisonous or irritant effects upon the human body. A "true gas" is a substance which is gaseous at ordinary temperatures. A "persistent gas" is usually a liquid at ordinary temperatures but evaporates slowly, giving off dangerous vapour. A "contaminating gas" is one which remains on an object or person and necessitates special treatment for the removal of it.

The best known examples are:

True gases—chlorine. phosgene.

Persistent gases—mustard gas. many lachrymatory gases.

Contaminating gases—mustard gas. lewisite.

Particulars regarding each of these gases will be found in the Air-Raid Precautions Handbook No. 1.