Gas masks are tight-fitting devices designed to protect the wearer from exposure to dangerous airborne bacteria, viruses, chemicals and vaporized poisons. Most gas masks seal off the wearer's nose and mouth to protect the airway, but some models include protective eye goggles and full hoods. Gas masks are not to be confused with oxygen masks or scuba masks, which import fresh air from a closed tank. Gas masks filter the outside air as it exists, without the addition of fresh breathable gases.
No one inventor can lay claim to the original gas mask design, although many sources give major credit to an African-American soldier working during WWI. Soldiers exposed to airborne poisons would often urinate on a cloth and cover their mouths and noses with it. The ammonia in the urine would chemically neutralize the chlorine gases commonly used on the battlefield during WWI. Further refinements created gas masks capable of filtering or neutralizing more advanced nerve agents like mustard gas, but the use of chemical warfare had waned considerably by the beginning of WWII. Soldiers would routinely discard their gas masks once the battlefield had been secured.
Gas masks protect the wearer through three separate methods. Many pollutants have particles larger than oxygen and nitrogen atoms, so the first line of defense is filtration. Most gas masks use a replaceable filter with an extremely fine mesh to physically block incoming particles such as smoke or virus-laden powders. The main problem with such a filtration system is that any mesh tight enough to block microscopic particles will also restrict the flow of clean air. The wearer may not feel enough breathable air is available with the filter in place.
Another means of air purification in gas masks is absorption. Vaporized liquid poisons and germs may be drawn away from the user's airway by absorbent chemicals such as activated charcoal. These absorbent chemicals may be held in a canister below the breathing chamber or impregnated in the filter. The main drawback to the absorption method is the limited number of poisonous gases which would be attracted to the chemicals. These types of gas masks would be most helpful in a factory setting where the pollutant was a known entity.
The final air purification method used in gas masks is chemical neutralization. This is what the soldiers in WWI were doing with their homemade ammonia masks. A canister containing a chemical or gas is attached under the face plate and the fumes interact with the incoming poison, rendering it chemically neutral, or at least harmless for respiration. This method is used extensively in situations where chemical warfare is possible. The major drawback is the somewhat unpleasant atmosphere created by the neutralizing agent.
Gas masks are available to the general public through medical supply stores, military surplus operations and specialized dealers. Workers who may be exposed to dangerous fumes are urged to wear some form of gas mask to protect their respiratory systems. For long-term exposure situations, however, a self-contained respirator system with a fresh air supply may be more useful.