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The gas mask is a mask used to protect the user 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. Some gas masks are also respirators, though the word ''gas mask'' is often used to refer to military equipment (e.g. Field Protective Mask). The user of the gas mask is not protected from gas that the skin can absorb. Most gas mask filters will last around 24 hours in an NBC (nuclear biological chemical) situation. Airborne toxic materials may be gaseous (for example sulfur mustard and chlorine gas used in World War I) or particulates (such as many biological agents developed for weapons such as bacteria, viruses and toxins). Many gas masks include protection from both types. Gas masks are used in construction to protect against welding fumes, in deconstruction 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, 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 with a big full-face window. Some have one or two filters attached to the face mask while others have a large filter connected to the face mask via a hose. ==Principles of construction== Absorption is the process of being drawn into a (usually larger) body, or substrate, and adsorption is the process of deposition upon a surface. This can be used to remove both particulate and gaseous hazards. Although some form of reaction may take place, it is not necessary; the method may work by attractive charges, for example, if the target particles are positively charged, use a negatively charged substrate. Examples of substrates include activated carbon, and zeolites. This effect can be very simple and highly effective, for example using a damp cloth to cover the mouth and nose whilst escaping a fire. While this method can be effective at trapping particulates produced by combustion, it does not filter out harmful gases which may be toxic or which displace the oxygen required for survival. File:US Navy gas mask excerise 021015-N-6996M-589.jpg|MCU-2/P Protective Mask on a U.S. Navy member. The filter cartridge is on the left side of the mouth, which makes it easier to aim a rifle right-handedly. File:US Navy 061027-N-4515N-227 Explosive Ordnance Technician 2nd Class Ian Jordan and Lt. j.g. Eric Hui from Explosive Ordnance Disposal Mobile Unit Two (EODMU-2), run tests on substances for an exercise on chemical warfare.jpg|US Navy EOD M45 gas mask system. Image:Gas mask 501556 fh000007.jpg|Gas mask used by the French military. The filter cartridge is connected via a flexible hose. File:Gas mask greek.jpg|Greek Infantry with US M17 gas masks 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gas mask」の詳細全文を読む スポンサード リンク
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