gas mask filter

A gas mask is a mask used to protect the wearer from inhaling airborne pollutants and toxic gases. The mask forms a sealed cover over the nose and mouth, but may also cover the eyes and other vulnerable soft tissues of the face. Most gas masks are also respirators, though the word gas mask is often used to refer to military equipment (such as a field protective mask). The gas mask only protects the user from digesting, inhaling and contact through the eyes (many agents affect through eye contact). Most combined gas mask filters will last around 8 hours in a nuclear biological chemical (NBC) situation. Chemical specific filters can last up to 20 hours in an NBC situation.
Airborne toxic materials may be gaseous (for example, mustard gas and chlorine gas) or particulates (such as biological agents). Many gas masks include protection from both types. Gas masks are used in construction to protect against welding fumes, in demolition to protect against asbestos or other hazardous particles, and in the chemical industry when handling hazardous materials, as in making repairs to leaking equipment or cleaning up after spills; workers are usually issued gas masks as a precaution against leaks.
During demonstrations and protests where tear gas or CS gas is employed by riot police, gas masks are commonly used by police and demonstrators alike. Aside from serving their functional purposes, gas masks are also used as emblems in industrial music, with the most notable example, the subgenre of drum and bass called neurofunk. These emblems are used by graffiti taggers because the mask protects them from the paint canister's toxic fumes, and by urban explorers venturing into environments where hazardous materials, such as asbestos, may be present.
The traditional gas mask style with two small circular eye windows originated when the only suitable material for these eye windows was glass or acrylic; as glass is notoriously brittle, glass eye windows had to be kept small and thick. Later, the discovery of polycarbonate allowed for gas masks to have a panoramic lens although the gas mask did not see this implemented until a long time after polycarbonate began to be used for gas mask lenses. Polycarbonate meant that lenses could be larger and so enabled a larger field of view. Some have one or two filters screwed (via inlets) onto to the gas mask while others have a large filter (coffee can filter) connected to the gas mask with a hose that is sometimes confused with an air-supplied respirator in which an alternate supply of fresh air (oxygen tanks) is delivered.

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