A gas mask can be a key component for a number of Halloween costumes, including a S.W.A.T. team member, a soldier or a Hazmat cleaner.
Don military fatigues or, for a S.W.A.T. team member, black trousers and a navy T-shirt.
Put on a bulletproof vest. If you can't get an authentic chest protector, any black vest will suffice.
Strap on the gas mask. Paint some camouflage print on it if you're going for the soldier look.
Add a helmet.
Complete the look with accessories, such as a fake gun, walkie-talkies or a riot shield.
Buy a chemical suit or other protective wear. Look online or visit a hardware store and look in the section stocked with chemicals or paints.
Put on the Hazmat suit, with the hood over your head.
Pull on rubber gloves and boots.
Add the gas mask.
You can label the Hazmat suit with the words "HAZMAT UNIT" to add realism. Use a permanent marker or sticker letters.