Part of a War-time anti-gas outfit.
Issued to everyone in a combat zone.
Asphyxiant gases just plug up your lungs and make it hard enough to breathe that, generally, you die from it. These include Chlorine, as used in the early part of the First War.
Blister gases were developed later. If you get them on your skin, they will eat away at you, give nice big suppurating blisters. Even a mild case will give you nice welts and raw spots. If you inhale the stuff, it does the same thing to your bronchia, nose, sinuses and lungs.
On hitting gas, first thing you did was cover your eyes, nose and mouth, breathe through the mask. One whiff of the stuff and you gave yourself a shot of Atropine; there would have been a single injection in your kit. Once you have had the Atropine, you should be able to breathe easier; it opens out the bronchial passages. Then you got into as much cover as you could (I suspect this is where your Cover comes in) and cleaned the gas off your skin, clothing, weapon and anything else that was contaminated.
Fortunately, gas was used very little in the Second War, at least in the West. The Russian Front was a whole different set of rules, as the USSR had never signed the Conventions and refused to admit the legality of the Hague Convention of 1899/1900 which the Imperial Government had signed.
Hope this helps.
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