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A gas mask is a mask put on over the face 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. 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.
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. 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 after spills; workers are usually issued gas masks as a precaution against leaks.
During riots where tear gas or CS-gas is employed by riot police, gas masks are commonly used by police and rioters 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 graffiti 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, discovery of polycarbonate allowed gas masks with a big full-face window. Some have one or two filters attached to the face piece; others have a large filter connected to the face piece by 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.
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.
Gas mask used by the French military. The filter cartridge is connected via a flexible hose.
Safety of old gas masks 
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 before 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 even potentially cause harm to the user due to long-term changes in the filter chemical composition.
World War II gas masks contained blue asbestos in their filters. It is unknown how long for certain the material was used in filters. Breathing blue asbestos in the factories resulted in the death of 10% of the workforce due to pleural and peritoneal mesothelioma. This rate was between 2.5 and 3.2 times the normal incidence of lung or respiratory cancers.
Many scare stories have originated from various Russian gas masks and their filters that are now common in surplus stores; the GP-5 was often considered to have an asbestos filter, however like most cold-war masks it only contains activated charcoal.
Modern gas masks are quite safe and do not use asbestos, but it is still important to be careful when using a modern gas mask. Typically masks using 40mm connections are more recent design. Rubber also degrades with time so new in box "Modern type" masks can be cracked and leak.
Filter classification 
The filter is selected according to the toxic compound. Each filter type protects against a particular hazard:
- AX - Low-boiling (≤65 °C) organic compounds
- A - High-boiling (>65 °C) organic compounds
- B - Inorganic gases (hydrogen sulfide, chlorine, hydrogen cyanide)
- E - Sulfur dioxide and hydrogen chloride (acidic gases)
- K - Ammonia and amines
- CO - Carbon monoxide
- Hg - Mercury
- Reactor - Iodine and methyl iodide (radioactive)
- P - Particles; classified as P1, P2, and P3 according to removal efficiency
- ABEK, ABEK-P3, ABEK-HgP3 or other combination filters against multiple hazards
Particle filters are often included, because in many cases, the hazardous materials are in the form of mist, which is captured already by the particle filter before entering the chemical adsorber. Filtration may be aided with an air pump to improve wearer comfort. Filtration of air is only possible if there is sufficient oxygen in the first place. Thus, when handling asphyxiants, or when ventilation is poor or the hazards are unknown, filtration is not possible and air must be supplied from a pressurized bottle as in scuba diving. Also, a gas mask does not protect against other hazards; for example, corrosive gases can damage the skin, requiring full-body protection.
Use of a mask 
A modern mask typically is constructed of an elastic polymer in various sizes. It is fitted with various adjustable straps which may be tightened to secure a good fit. Crucially, it is connected to a filter cartridge near the mouth either directly, or via a flexible hose. Some models contain drinking tubes which may be connected to a water bottle. Corrective lens inserts are also available for users who require them.
Masks are typically tested for fit before use. After a mask is fitted, it is often tested by various challenge agents. Isoamyl acetate, a synthetic banana flavorant, and camphor are often used as innocuous challenge agents. In the military, teargases such as CN, CS, and stannic chloride in a chamber may be used to give the users confidence in the efficacy of the mask.
When the mask is used in a real scenario, or as part of a drill, there is 9 seconds to put the gas mask on and clear and seal. Hold the breath and close the eyes, pulling the gas mask out of its carrying case and put the mask on, exhale hard to purge any contaminants from the interior of the mask, put a hand over the canister hole, and take a breath: the mask should collapse onto the face to provide a seal. Once the mask is cleared and sealed, tighten the straps. The wearer may put on further protective clothing after the mask.
Reaction and exchange 
This principle relies on substances harmful to humans being 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 synthetic resins. These can be created with different groups of atoms (usually called functional groups) that have 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 poison gas was used more often, more sophisticated gas masks were developed and introduced. There are two main difficulties with gas mask design:
- The user may be exposed to many 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. Thus the user only has protection for a limited time, and then he must either replace the filter device in the mask, or use a new mask.
History and development of the gas mask 
According to Popular Mechanics, "The common sponge was used in ancient Greece as a gas mask..." An early type of rudimentary gas mask was invented in the 9th century by the Banu Musa brothers in Baghdad, Iraq. They described it in their Book of Ingenious Devices,[verification needed] mainly for protecting workers in polluted wells.
Primitive respirator examples were used by miners and introduced by Alexander von Humboldt already in 1799, when he worked as a mining engineer in Prussia; long before that there was a Plague doctor's bird beak shaped mask/face piece filled with herbs.
The forerunner to the modern gas mask was invented in 1847 by Lewis Haslett, a device that contained elements that allowed breathing through a nose and mouthpiece, inhalation of air through a bulb-shaped filter, and a vent to exhale air back into the atmosphere. According to First Facts, it states that the "gas mask resembling the modern type was patented by Lewis Phectic Haslett of Louisville, Kentucky who received a patent on June 12, 1849."  U.S. patent #6,529 issued to Haslett, described the first "Inhaler or Lung Protector" that 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.
Another early design was the "Safety Hood and Smoke Protector" invented by Garrett 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.
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 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.
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.
American chemist and inventor James Bert Garner is credited by American sources with the invention of the gas mask in April 1915. Reading a newspaper article describing a gas attack on British forces which he hypothesized had employed chlorine gas, Garner remembered experiments he had performed while teaching at the University of Chicago, thus 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 of 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. In addition gas mask were developed during World War One and after for horses in the various mounted units that operated near the front lines.
The modern gas mask that people in the USA are familiar with today was developed in 1944 by the US Army Chemical Warfare Service. It was made of plastic and rubber-like material that greatly reduced the weight and bulk compared to World War One gasmasks and fitted the user's face more snugly and comfortably. The main improvement was replacing the separate filter canister connected with a hose by a filter canister screwed on the side of the gas mask, that could be replaced easily. Also, it had replaceable plastic lenses, much helping vision.
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 buy gas masks believing 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 all NBC agents, they can have filter canisters proof against those agents (heavier) or only 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 which attracts all manner of pollutants from air and water. Pollutants do not react with the carbon but are adsorbed into the pores. 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 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 absorbent 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 stones performed much better than wood charcoal. These waste materials were collected from the public in recycling programs to assist the war effort.
See also 
- Acheson, E D; Gardner, M J; Pippard, E C; Grime, L P (1982). "Mortality of two groups of women who manufactured gas masks from chrysotile and crocidolite asbestos: a 40-year follow-up". Occupational and Environmental Medicine 39 (4): 344–8. doi:10.1136/oem.39.4.344. PMC 1009064. PMID 6291580.
- "Popular Mechanics". January 1984. p.163
- Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69. (cf. Donald Routledge Hill, Mechanical Engineering)
- Young, M. J. L. (1990). The Cambridge history of Arabic literature. Cambridge University Press. p. 264. ISBN 0-521-32763-6.
- "The invention of the gas mask". Ian Taggart.
- Drobnicki, John A.; Asaro, Richard (2001). "Historical Fabrications on the Internet". In Su, Di. Evolution in Reference and Information Services: The Impact of the Internet. Binghamton, New York: Haworth Information Press. p. 144. ISBN 978-0-7890-1723-9.
- "Lewis P". United States Patent and Trademark office.
- Victor Lefebure (1923). The Riddle of the Rhine: Chemical Strategy in Peace and War. The Chemical Foundation Inc. ISBN 0-585-23269-5.
- "The UK". The Gas Mask Database.
- "Gas mask inventor Harrison honoured in death by Churchill". Royal Society of Chemistry. Retrieved 2008-06-12.
- "Boone County Native Invented the Gas Mask". Ralph W. Stark.
- Pittsburgh Post-Gazette, November 30th, 1960
- Gas-Masks for Dogs / Dumb Heroes of the Fighting Front, Popular Science monthly, December 1918, page 75, Scanned by Google Books: http://books.google.com/books?id=EikDAAAAMBAJ&pg=PA75
- "Gas Masks to Guard Horses and Dogs in War" Popular Mechanics, July 1934 bottom pg. 75
- "Gas Mask Weighing Half As Much." Popular Sciences, March 1944, p. 74.
- Kozhevnikov, A.B. (2004). Stalin's great science: the times and adventures of Soviet physicists (illustrated, reprint ed.). Imperial College Press. pp. 10–11. ISBN 1-86094-419-1, 9781860944192 Check
|isbn=value (help). Retrieved 2009-04-28.
- Once Worthless Things that have Suddenly Become of Value, Popular Science monthly, December 1918, page 80, Scanned by Google Books: http://books.google.com/books?id=EikDAAAAMBAJ&pg=PA80
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- CBRN SCBA NIOSH Approved Respirators 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