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Gas mask
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A gas mask is a mask worn over the face to protect the wearer from inhaling "airborne pollutants" and toxic gasses. 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, etc.) (The user of the gas mask is not protected from gas that the skin can absorb.)
Airborne toxic materials may be gaseous (for example the chlorine gas used in World War I) or particulate (such as many biological agents developed for weapons such as bacteria, viruses and toxins).
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A gas mask is a mask worn over the face to protect the wearer from inhaling "airborne pollutants" and toxic gasses. 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, etc.) (The user of the gas mask is not protected from gas that the skin can absorb.)
Airborne toxic materials may be gaseous (for example the chlorine gas used in World War I) or particulate (such as many biological agents developed for weapons such as bacteria, viruses and toxins). Many gas masks include protection from both types. During riots where tear gas or CS-gas is employed by riot police, gas masks are commonly used by police and rioters alike.
Gas masks have a limited useful lifespan that is related to the absorbent capacity of the filter. Once the filter has been saturated with hazardous chemicals, it ceases to provide protection and the user may be injured. Most gas masks use sealing caps over the air intake to prevent the filter from degrading prior to use, but the protective abilities also degrade as the filter ages or if it is exposed to moisture and heat. Very old unused gas mask filters from World War II may not be effective at all in protecting the user, and can potentially cause harm to the user due to long-term changes in the filter chemical composition.
Aside from serving their functional purposes, gas masks are also used as emblems in Industrial music, and by graffiti taggers because the mask protects them from the graffiti canister's toxic fumes. Also closely related is the eroticization of gas masks as a sexual fetish.
The traditional gas mask style with two small circular eye windows originated when the only suitable material for these eye windows was glass or perspex; as glass is notoriously brittle, glass eye windows had to be kept small and thick. Later, discovery of polycarbonate allowed gas masks with a big fullface window, as .
Some have one or two filters attached to the face piece: . Some have a large filter connected to the face piece by a hose: .
Principles of construction
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.
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 zeolitess. 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.
Gas masks were used in World War II when the bomb siren sounded. Everybody had to keep a gas mask with them at all times, because a siren could go off at anytime. There was a popular saying that went "Lose Your Gas Mask, Lose Your Life!"
Reaction and exchange
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 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 less harmful substance at this site.
Though it was crude, the hypo helmet was a stopgap measure for British troops in the trenches that offered at least some protection during a gas attack. As the months passed and the use of poison gas occurred more frequently, more sophisticated masks were developed and introduced.
There are two main difficulties with gas mask design:
- The user may be exposed to many different types of toxic material. Military personnel 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 a limited time, and then they must either replace the filter device in the mask, or use a new mask.
History and development of the gas mask
A primitive respirator to be used by miners was introduced by Alexander von Humboldt already in 1799, when he worked as a mining engineer in Prussia.
The gas mask was patented on June 12, 1849, by American Lewis Haslett in Louisville, Kentucky. It was an "Inhaler or Lung Protector," issued for an air purifying respirator. Haslett's device filtered dust from the air.
Early versions were constructed by the Scottish chemist John Stenhouse in 1854 and the physicist John Tyndall in the 1870s.
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. In addition, moist sponges were inserted at the end of the hoses in order to better filter the air. 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.
The first use of poison gas on the Western Front was on 22 April 1915, by the Germans at Ypres, against Canadian and French colonial troops. The initial response was to equip troops with cotton mouth pads for protection. Soon afterwards the British added a long cloth which was used to tie chemical-soaked mouth pads into place, and which was called the Black Veil Respirator. Dr. Cluny MacPherson of The Royal Newfoundland Regiment brought the idea of a mask made of chemical absorbing fabric and which fitted over the entire head to England, and this was developed into the British Hypo Helmet of June 1915. This primitive type of mask went through several stages of development before being superseded in 1916 by the canister gas mask of 1916. This had a mask connected to a tin can containing the absorbent materials by a hose.
In 1915, American chemist and inventor credited with the invention of the gas mask James Bert Garner read a newspaper article describing a gas attack on British forces which he hypothesized had employed chlorine gas. Remembering experiments he had performed while teaching at the University of Chicago, he set about creating the first gas mask which he tested on two of his associates in a gas filled chamber. Following the successful completion of the test, he provided the results to the British government. Garner's mask was the first to be used on the Western front during World War I. Also in World War I, since dogs were frequently used on the front lines, a special type of gas mask was developed that dogs were trained to wear.
The British Royal Society of Chemistry claims that British scientist Edward Harrison developed the first practical gas mask for mass production, a claim supported by a thank-you note written by Winston Churchill.
In America thousands of gas masks were produced for American as well as Allied troops. Mine Safety Appliances was a chief producer. This mask was later used widely in industry.
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 from contact with the atmosphere. For reasons of civil defense and personal protection, individuals often purchase gas masks in the belief that they protect against the harmful effects of an attack with nuclear, biological, or chemical (NBC) agents; which is only partially true, 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 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.
History of Absorbents and Neutralizers
Activated charcoal is a common component of gas masks. It is a carbon with an extremely high surface area and which attracts all manner of pollutants from air and water. Pollutants do not react with the carbon but are bonded to it in a process called adsorption. Over time the activated carbon becomes thoroughly coated and it ceases to remove pollutants. However, the charcoal can be reactivated and restored to its original state by baking the charcoal with high heat, which either evaporates or burns off the pollutants.
In the first gas masks of World War I, it was initially found that wood charcoal was a good adsorbent of poison gases. In about 1918 it was found that charcoals made from the shells and seeds of various fruits and nuts such as coconuts, chestnuts, horse-chestnuts, and peach pits performed much better than wood charcoal. These waste materials from food products were collected from the public in recycling programs to assist the war effort.
See also
External links
- International historical gas mask gallery, with collection of safety and propaganda posters.
- Information on gas masks from many countries.
- Guide to selecting safe and dependable gas masks
- Guide to the maintenance of your gas mask
- List of NIOSH Approved CBRN SCBA respirators
- World War 1 gas mask technology - Combating Man's Deadliest Peril: How the unending struggle between gas and mask is carried on, Popular Science monthly, December 1918, page 64, Scanned by Google Books: http://books.google.com/books?id=EikDAAAAMBAJ&pg=PA64
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