Gas and dust masks offer their users protection against hazardous airborne substances, such as gases, fumes, and dusts that are toxic, irritants, or otherwise harmful. Some masks protect against airborne radioactive or biological hazards. Protective masks are often used in industrial environments and construction sites, where routine activities can liberate harmful substances, and they form part of the kit of military and security personnel, who can be exposed to deliberate nuclear, biological, or chemical (NBC) attacks.
Invention and early developments
The first gas mask was a breathing device patented in 1914 by Garrett A. Morgan, the U.S. inventor of the stoplight and numerous grooming products for African-American hair. Morgan’s gas mask consisted of a canvas hood with plain eyeglasses. Twin canvas hoses passed from the bottom of the hood under the wearer’s arms and merged into a single tube at the back. A water-soaked sponge in the tube filtered and cooled incoming air, making it easier to breathe in smoke-filled environments. Morgan’s device gained fame in 1916, when the inventor himself, his two brothers, and two volunteers rescued 20 suffocating construction workers from a smoke-filled tunnel under Lake Erie.
In World War I, a short time after Morgan’s invention, a different type of gas mask was used as a defense against chemical weapons that German forces used first against Russian soldiers, then against the Allied forces of Britain and France. These early gas masks had a canister that was worn behind the user’s back. The canister contained granules of activated charcoal, which served to absorb airborne chemicals, including poisonous gases. A tube led from one end of the canister to the user’s mouth, and a clip prevented accidental inhalation through the nose.
Apart from providing air that was fit to breathe, the device had an airtight face mask with eyeglasses that formed a barrier against poison gases. Eye protection was important, since gases such as phosgene (COCl2) and mustard gas react with moisture to form hydrochloric acid, which can irritate and cause permanent damage to the delicate tissues of the eyes if exposed.
In 1918, the original military gas masks were improved by the inclusion of hopcalite, a catalyst that eliminates carbon monoxide—a suffocating poisonous gas. Hopcalite functions by promoting a reaction between carbon monoxide and oxygen in the air to produce carbon dioxide.
Chemical filters
The principal method by which modern gas masks remove harmful chemicals from air is absorption, just as it was with World War I gas masks. Activated charcoal is still used in many modern filters, others use porous minerals called zeolites, which are particularly effective absorbers of moisture and acid gases. Such materials allow smaller molecules, such as oxygen and nitrogen, to pass through them with relative ease; larger molecules become trapped in their pores. After a while, the pores become saturated and the filter canister or cartridge has to be changed.
The useful life of absorption filters depends on the concentration of absorbable materials in the air: the greater their concentration, the quicker the pores become full. The rate at which a filter reaches saturation also depends on the wearer’s level of activity, since a running soldier or firefighter will draw more breaths in a given period of time than will a calm, seated person.
Absorbent filters are of little use against harmful materials that are either too small to be trapped in their pores or too large to even enter them. Ammonia, carbon monoxide, formaldehyde, and certain acidic gases can be destroyed only by filters containing substances that react with such compounds and make them harmless. Acid gases can be neutralized by basic compounds, for example, while ammonia and simple amines can be eliminated by metal salts that bind them in stable compounds.
