The mask debate

A gas mask, also known as a respirator, is a mask worn on the face to protect the body from airborne pollutants and toxic materials. 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.

Airborne toxic materials may be gaseous (for example the chlorine used in WWI) or particulate (such as many biological agents developed for weapons such as bacteria, viruses and toxins). Many gas masks include protection from both types. Unlike other breathing devices, gas masks do not require the user to carry an air supply as in the use of scuba gear. However, this means that the wearer depends on the air in the atmosphere, the same medium of the toxic materials. Thus, the mask must remove them and relay clean air to the wearer.

There are three main ways of achieving this: filtration, absorption and adsorption, and reaction and exchange.

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Filtration

A filter works by having holes that are smaller than the particles to be removed. Since many pollutant molecules and particles are larger than oxygen and nitrogen molecules, this works for many applications. Filtration thus lends itself to defense against particulate hazards.

Gas-masked US Navy member in a MILES combat exercise

However, the smaller the gap through which the air has to pass, the greater the pressure the wearer's lungs must exert to draw the air through, hereby limiting the porosity of these passages. Thus to extract many toxic gases, masks use other methods.

Absorption and adsorption

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. Most of the harmful vapours and smoke will be dissolved in the water on the cloth, giving you vital extra seconds to escape.

Reaction and exchange

Gas mask used by the French military

This principle relies upon the fact that substances that can do harm to humans are usually more reactive than air. This method of separation will use some form of generally reactive substance (for example an acid) coating or supported by some solid material. An excellent example is resins. These can be created with different groups of atoms (usually called functional groups) that exhibit different properties. Thus a resin can be tailored to a particular toxic group. When the reactive substance comes in contact with the resin, it will bond to it, removing it from the air stream. It may also exchange with a more harmless substance at this site.

There are two main difficulties with gas-mask design:

• The user may be exposed to many different types of toxic material. Military personel are especially prone to being exposed to a diverse range of toxic gases. However if the mask is for a particular use (such as the protection from a specific toxic material in a factory), then the design can be much simpler and the cost lower.

• The protection will wear off over time. Filters will clog up, substrates for absorption will fill up, and reactive filters will run out of reactive substance. This means that the user only has protection for so long, and then they must either replace the filter device in the mask, or use a new mask.

History and development of the gas mask

Contrary to some modern day opinion, there is no single inventor of the "gas mask". In fact, there were patents for such devices as early as 1887. A first gas mask to be used by miners was introduced by Alexander von Humboldt already in 1799, when he worked as a mining engineer in Prussia.

Early gas mask designed by A. von Humboldt in 1799 for underground mining

In the early days of World War I, the Canadian Army made field expedient gas masks to protect themselves from the deadly chlorine gas used by the Germans by urinating on rags and holding them to their faces.

One such design began as a "Safety Hood and Smoke Protector" invented by African American inventor, Garrett A. Morgan in 1912, and patented in 1914. It was a simple device, consisting of a cotton hood with two hoses which hung down to the floor, allowing the wearer to breathe the safer air found there. Morgan won acclaim for his device when in 1916 he, his brother, and two other volunteers used his device to rescue numerous men from the gas and smoke-filled tunnels beneath Lake Erie in the Cleveland Waterworks.

Dr. Cluny MacPherson of The Royal Newfoundland Regiment, while serving in Gallipoli in 1915, where he acted as an advisor on poisonous gas, used a helmet taken from a captured prisoner to fashion a canvas hood with transparent eyepieces that was treated with chlorine-absorbing chemicals.

Gas masks development since has mirrored the development of chemical agents in warfare, filling the need to protect against ever more deadly threats, biological weapons, and radioactive dust in the nuclear era. However, where agents that cause harm through contact or penetration of the skin occurs, such as blister agent or nerve agent, a gas mask alone is not sufficient protection, and full protective clothing must be worn in addition, to protect contact from the atmosphere. For reasons of civil defense and personal protection, individuals often purchase gas masks in the belief that they prevent against the harmful effects of an attack with nuclear, biological, or chemical (NBC) agents; this is not the case, as gas masks protect only against respiratory absorption. Whilst most military gas masks are designed to be capable of protection against spectrum of NBC agents, they can be coupled with filter canisters that are proof against those agents (heavier) or just against riot control agents and smoke (lighter, and often used for training purposes); likewise there are lightweight masks solely for use in riot control agents and not for NBC situations.

Although thorough training and the availability of gas masks and other protective equipment can render the casualty-causing effects of an attack by chemical agents nullified, troops who are forced to operate in full protective gear are less efficient in completing their given tasks, tire easily, and may be affected psychologically by the threat of attack by these weapons. During the Cold War era, it was seen as inevitable that there would be a constant NBC threat on the battlefield, and thus troops needed protection in which they could remain fully functional; thus protective gear, and especially gas masks have evolved to incorporate welcomed innovations in terms of increasing user-comfort, and in compatibility with other equipment (from drinking devices to artificial respiration tubes, to communications systems etc). The gas mask has thus now arrived at a 'fourth generation' of development.