Filters and gas masks are used to shield from the toxic effects of biological and chemical agents. It protects us from chemicals like hydrogen cyanide, chlorine, phosgene, mustard agent, and these chemicals were used during World War I. These chemicals caused several casualties among allied forces and created the need for protective masks.
Since then gas masks have evolved and protected against all types of known chemical and biological agents. Gas masks use various techniques to shield the user. But the common components like eyepieces, facepiece, hood, and filters are present in almost all masks. Check out here to find various types of modern gas mask and protective hood systems.
The most basic mask uses the filtration technique. Pollutants generally have larger particles than oxygen and by using a fine mesh these can be kept out. The other process uses the absorbing qualities of specific chemicals such as activated charcoal to manage the harmful agents.
Such masks have limited use, as they can absorb only a few chemicals. The present-day masks use the method of chemical neutralization. These masks contain chemical filters that neutralize the harmful chemicals present in the air.