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A gas mask is a
mask A mask is an object normally worn on the face, typically for protection, disguise, performance, or entertainment and often they have been employed for rituals and rights. Masks have been used since antiquity for both ceremonial and pra ...
used to protect the wearer from inhaling airborne
pollutant A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like o ...
s 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. Most gas masks are also
respirator A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including fumes, vapours, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main categories of resp ...
s, though the word ''gas mask'' is often used to refer to military equipment (such as a field protective mask), the scope used in this article. The gas mask only protects the user from digesting, inhaling, and contact through the eyes (many agents affect through eye contact). Most combined gas mask filters will last around 8 hours in a biological or chemical situation. Filters against specific chemical agents can last up to 20 hours. Airborne toxic materials may be gaseous (for example,
chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...
or
mustard gas Mustard gas or sulfur mustard is a chemical compound belonging to a family of cytotoxic and blister agents known as mustard agents. The name ''mustard gas'' is technically incorrect: the substance, when dispersed, is often not actually a gas, b ...
), or particulates (such as biological agents). Many filters provide protection from both types. The first gas masks mostly used circular lenses made of
glass Glass is a non-Crystallinity, crystalline, often transparency and translucency, transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most ...
,
mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
or
cellulose acetate In biochemistry, cellulose acetate refers to any acetate ester of cellulose, usually cellulose diacetate. It was first prepared in 1865. A bioplastic, cellulose acetate is used as a film base in photography, as a component in some coatings, ...
to allow vision. Glass and mica were quite brittle and needed frequent replacement. The later Triplex lens style (a cellulose acetate lens sandwiched between glass ones) became more popular, and alongside plain cellulose acetate they became the standard into the 1930s. Panoramic lenses were not popular until the 1930s, but there are some examples of those being used even during the war (Austro-Hungarian 15M). Later, stronger
polycarbonate Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...
came into use. Some masks have one or two compact air filter containers screwed onto inlets, while others have a large air filtration container connected to the gas mask via a hose that is sometimes confused with an ''air-supplied respirator'' in which an alternate supply of fresh air (oxygen tanks) is delivered.


Principles of construction

Absorption is the process of being drawn into a (usually larger) body or substrate, and
adsorption Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which ...
is the process of deposition upon a surface. This can be used to remove both particulate and gaseous hazards. Although some form of
reaction Reaction may refer to a process or to a response to an action, event, or exposure: Physics and chemistry *Chemical reaction *Nuclear reaction *Reaction (physics), as defined by Newton's third law * Chain reaction (disambiguation). Biology and me ...
may take place, it is not necessary; the method may work by attractive
charges Charge or charged may refer to: Arts, entertainment, and media Films * '' Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * ''Charge'' (David Ford album) * ''Charge'' (Machel Montano album) * ''Charge!!'', an album by The Aqu ...
. For example, if the target particles are positively charged, a negatively charged substrate may be used. Examples of substrates include
activated carbon Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area avail ...
, and
zeolite Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These ...
s. This effect can be very simple and highly effective, for example using a damp cloth to cover the mouth and nose while 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 exercise 021015-N-6996M-589.jpg, US Navy MCU-2/P gas mask system. File: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


Safety of old gas masks

Gas masks have a useful lifespan limited by the absorbent capacity of the filter. Filters cease to provide protection when saturated with hazardous chemicals, and degrade over time even if sealed. Most gas masks have sealing caps over the air intake and are stored in vacuum-sealed bags to prevent the filter from degrading due to exposure to humidity and pollutants in normal air. Unused gas mask filters from World War II may not protect the wearer at all, and could be harmful if worn due to long-term changes in the chemical composition of the filter. Some World War II and Soviet Cold War gas masks contained
chrysotile asbestos Chrysotile or white asbestos is the most commonly encountered form of asbestos, accounting for approximately 95% of the asbestos in the United StatesOccupational Safety and Health Administration, United States Department of Labor, U.S. Departmen ...
or crocidolite asbestos in their filters, not known to be harmful at the time. It is not reliably known for how long the materials were used in filters. Typically, masks using 40 mm connections are a more recent design. Rubber degrades with time, so boxed unused "modern type" masks can be cracked and leak. The US C2 canister (black) contains hexavalent chromium; studies by the U.S. Army Chemical Corps found that the level in the filter was acceptable, but suggest caution when using, as it is a
carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subst ...
.


Modern filter classification

The filter is selected according to the toxic compound. Each filter type protects against a particular hazard and is color-coded: Particle filters are often included, because in many cases the hazardous materials are in the form of mist, which can be captured by the particle filter before entering the chemical adsorber. In Europe and jurisdictions with similar rules such as Russia and Australia, filter types are given suffix numbers to indicate their capacity. For non-particle hazards, the level "1" is assumed and a number "2" is used to indicate a better level. For particles (P), three levels are always given with the number. In the US, only the particle part is further classified by NIOSH air filtration ratings. A filter type that can protect against multiple hazards is notated with the European symbols concatenated with each other. Examples include ABEK, ABEK-P3, and ABEK-HgP3. A2B2E2K2-P3 is the highest rating of filter available. An entirely different "multi/CBRN" filter class with an olive color is used in the US. 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
asphyxiant An asphyxiant gas, also known as a simple asphyxiant, is a nontoxic or minimally toxic gas which reduces or displaces the normal oxygen concentration in breathing air. Breathing of oxygen-depleted air can lead to death by asphyxiation (suffocat ...
s, or when ventilation is poor or the hazards are unknown, filtration is not possible and air must be supplied (with a SCBA system) from a pressurized bottle as in scuba diving.


Use

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 flavourant, and
camphor Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel ('' Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the k ...
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.


Shortcomings

The protection of a gas mask comes with some disadvantages. The wearer of a typical gas mask must exert extra effort to breathe, and some of the exhaled air is re-inhaled due to the dead space between the facepiece and the user's face. The exposure to
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
may exceed its OELs (0.5% by volume/9 grammes per cubic metre for an eight-hour shift; 1.4%/27 grammes per m3 for 15 minutes' exposure) by a factor of many times: for gas masks and
elastomeric respirator Elastomeric respirators, also called reusable air-purifying respirators, seal to the face with elastomeric material, which may be a natural or synthetic rubber. They are generally reusable. Full-face versions of elastomeric respirators seal bet ...
s, up to 2.6%);copy
/ref> and in case of long-term use,
headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a resul ...
,
dermatitis Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...
and
acne Acne, also known as ''acne vulgaris'', is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples, oily skin, and ...
may appear. The UK HSE textbook recommends limiting the use of respirators without air supply (that is, not PAPR) to one hour.


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 resin Synthetic resins are industrially produced resins, typically viscous substances that convert into rigid polymers by the process of curing. In order to undergo curing, resins typically contain reactive end groups, such as acrylates or epoxides. ...
s. These can be created with different groups of
atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas ...
s (usually called
functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the res ...
s) 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 substances. Thus 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. File:Humboldt gasmask 1799.jpg, A primitive respirator was designed by Alexander von Humboldt in 1799 for underground mining File:Various gas masks WWI.jpg, Various gas masks employed on the
Western Front Western Front or West Front may refer to: Military frontiers *Western Front (World War I), a military frontier to the west of Germany *Western Front (World War II), a military frontier to the west of Germany *Western Front (Russian Empire), a majo ...
and Eastern Front during World War I File:1930s gas mask.jpg, Finnish civilian gas mask from 1939. These masks were distributed during World War II File:A mother and baby both in gas-masks during 1941. D3918.jpg, Mother and baby with gas masks, 1941


History and development


Early breathing devices

According to ''
Popular Mechanics ''Popular Mechanics'' (sometimes PM or PopMech) is a magazine of popular science and technology, featuring automotive, home, outdoor, electronics, science, do-it-yourself, and technology topics. Military topics, aviation and transportation o ...
'', "The common sponge was used in
ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...
as a gas mask..." In 1785, Jean-François Pilâtre de Rozier invented a
respirator A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including fumes, vapours, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main categories of resp ...
. Primitive respirator examples were used by
miner A miner is a person who extracts ore, coal, chalk, clay, or other minerals from the earth through mining. There are two senses in which the term is used. In its narrowest sense, a miner is someone who works at the rock face; cutting, blasting ...
s and introduced by
Alexander von Humboldt Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 17696 May 1859) was a German polymath, geographer, naturalist, explorer, and proponent of Romantic philosophy and science. He was the younger brother of the Prussian minister, ...
in 1799, when he worked as a mining engineer in
Prussia Prussia, , Old Prussian: ''Prūsa'' or ''Prūsija'' was a German state on the southeast coast of the Baltic Sea. It formed the German Empire under Prussian rule when it united the German states in 1871. It was ''de facto'' dissolved by an ...
. The forerunner to the modern gas mask was invented in 1847 by Lewis P. 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. ''First Facts'' states that a "gas mask resembling the modern type" was patented by Lewis Phectic Haslett of
Louisville, Kentucky Louisville ( , , ) is the largest city in the Commonwealth of Kentucky and the 28th most-populous city in the United States. Louisville is the historical seat and, since 2003, the nominal seat of Jefferson County, on the Indiana borde ...
, 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 Garrett Augustus Morgan, Sr. (March 4, 1877 – July 27, 1963) was an American inventor, businessman, and community leader. His most notable inventions were a three-position traffic signal and a smoke hood (a predecessor to the gas mask) notably ...
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. This was later modified to include its own air supply, leading to World War I era gas masks.


First World War

The First World War brought about the first need for mass-produced gas masks on both sides because of extensive use of chemical weapons. The German army successfully used
poison gas Many gases have toxic properties, which are often assessed using the LC50 (median lethal dose) measure. In the United States, many of these gases have been assigned an NFPA 704 health rating of 4 (may be fatal) or 3 (may cause serious or perm ...
for the first time against Allied troops at the Second Battle of Ypres, Belgium on April 22, 1915. An immediate response was cotton wool wrapped in muslin, issued to the troops by May 1. This was followed by the
Black Veil Respirator The Black Veil Respirator was an early British gas mask designed by John Scott Haldane and introduced in May 1915. History The German army used chlorine as a poison gas for the first time against Allied troops at the Second Battle of Ypres on 2 ...
, invented by
John Scott Haldane John Scott Haldane (; 2 May 1860 – 14/15 March 1936) was a British physician and physiologist famous for intrepid self-experimentation which led to many important discoveries about the human body and the nature of gases. He also experimen ...
, which was a cotton pad soaked in an absorbent solution which was secured over the mouth using black cotton veiling. Seeking to improve on the Black Veil respirator, Cluny MacPherson created a mask made of chemical-absorbing fabric which fitted over the entire head. A canvas hood treated with chlorine-absorbing chemicals, and fitted with a transparent mica eyepiece. Macpherson presented his idea to the British War Office Anti-Gas Department on May 10, 1915; prototypes were developed soon after. The design was adopted by the British Army and introduced as the British Smoke Hood in June 1915; Macpherson was appointed to the War Office Committee for Protection against Poisonous Gases. More elaborate sorbent compounds were added later to further iterations of his helmet ( PH helmet), to defeat other respiratory poison gases used such as
phosgene Phosgene is the organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. Phosgene is a valued and important industrial building block, es ...
, diphosgene and
chloropicrin Chloropicrin, also known as PS and nitrochloroform, is a chemical compound currently used as a broad-spectrum antimicrobial, fungicide, herbicide, insecticide, and nematicide. It was used as a poison gas in World War I. Its chemical structural for ...
. In summer and autumn 1915, Edward Harrison,
Bertram Lambert Bertram may refer to: Places *Bertram, Western Australia, a suburb of Perth, Australia * Bertram, Iowa, United States, a city *Bertram, Texas, United States, a city *Bertram Building, a historic building in Austin, Texas *Bertram Glacier, Palmer La ...
and John Sadd developed the
Large Box Respirator Large means of great size. Large may also refer to: Mathematics * Arbitrarily large, a phrase in mathematics * Large cardinal, a property of certain transfinite numbers * Large category, a category with a proper class of objects and morphisms (or ...
. This canister gas mask had a tin can containing the absorbent materials by a hose and began to be issued in February 1916. A compact version, the Small Box Respirator, was made a universal issue from August 1916. In the first gas masks of World War I, it was initially found that wood charcoal was a good absorbent of poison gases. Around 1918, it was found that charcoals made from the shells and seeds of various fruits and nuts such as
coconut The coconut tree (''Cocos nucifera'') is a member of the palm tree family (Arecaceae) and the only living species of the genus ''Cocos''. The term "coconut" (or the archaic "cocoanut") can refer to the whole coconut palm, the seed, or ...
s,
chestnut The chestnuts are the deciduous trees and shrubs in the genus ''Castanea'', in the beech family Fagaceae. They are native to temperate regions of the Northern Hemisphere. The name also refers to the edible nuts they produce. The unrelate ...
s, horse-chestnuts, and
peach The peach (''Prunus persica'') is a deciduous tree first domesticated and cultivated in Zhejiang province of Eastern China. It bears edible juicy fruits with various characteristics, most called peaches and others (the glossy-skinned, non- ...
stones performed much better than wood charcoal. These waste materials were collected from the public in recycling programs to assist the war effort. The first effective filtering
activated charcoal "Activated" is a song by English singer Cher Lloyd. It was released on 22 July 2016 through Vixen Records. The song was made available to stream exclusively on ''Rolling Stone'' a day before to release (on 21 July 2016). Background In an inter ...
gas mask in the world was invented in 1915 by Russian chemist Nikolay Zelinsky. 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. Other gas masks were developed during World War I and the time following for horses in the various mounted units that operated near the front lines. In America, thousands of gas masks were produced for American as well as Allied troops.
Mine Safety Appliances Mine Safety Appliances, or MSA Safety Incorporated, is an American manufacturer and supplier of safety equipment designed for use in a variety of hazardous conditions in industries such as construction, the military, fire service, and chemical, ...
was a chief producer. This mask was later used widely in industry.Pittsburgh Post-Gazette, November 30, 1960


Second World War

The British Respirator, Anti-Gas (Light) was developed in 1943 by the British. It was made of plastic and rubber-like material that greatly reduced the weight and bulk compared to World War I gas masks, and fitted the user's face more snugly and comfortably. The main improvement was replacing the separate filter canister connected with a hose by an easily replaceable filter canister screwed on the side of the gas mask. Also, it had replaceable plastic lenses.


Modern mask

Gas mask 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, for agents that cause harm through contact or penetration of the skin, such as
blister agent A blister agent (or vesicant), is a chemical compound that causes severe skin, eye and mucosal pain and irritation. They are named for their ability to cause severe chemical burns, resulting in painful water blisters on the bodies of those affec ...
or
nerve agent Nerve agents, sometimes also called nerve gases, are a class of organic chemicals that disrupt the mechanisms by which nerves transfer messages to organs. The disruption is caused by the blocking of acetylcholinesterase (AChE), an enzyme that ...
, 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 defence and personal protection, individuals often buy gas masks since they believe 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. Most military gas masks are designed to be capable of protecting against all NBC agents, but they can have filter canisters proof against those agents (heavier) or only against
riot control agent Riot control measures are used by law enforcement, military, paramilitary or security forces to control, disperse, and arrest people who are involved in a riot, unlawful demonstration or unlawful protest. If a riot is spontaneous and irr ...
s and smoke (lighter and often used for training purposes). There are lightweight masks solely for protection against riot-control agents and not for NBC situations. Although thorough training and the availability of gas masks and other protective equipment can nullify the casualty-causing effects of an attack by chemical agents, troops who are forced to operate in full protective gear are less efficient in completing tasks, tire easily, and may be affected psychologically by the threat of attack by those weapons. During the Cold War, it was seen as inevitable that there would be a constant NBC threat on the battlefield and so 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 compatibility with other equipment (from drinking devices to artificial respiration tubes, to communications systems etc.). During the
Iran–Iraq War The Iran–Iraq War was an armed conflict between Iran and Iraq that lasted from September 1980 to August 1988. It began with the Iraqi invasion of Iran and lasted for almost eight years, until the acceptance of United Nations Security Counci ...
(1980–88), Iraq developed its chemical weapons program with the help of European countries such as Germany and France and used them in a large scale against Iranians and Iraqi Kurds. Iran was unprepared for chemical warfare. In 1984, Iran received gas masks from the
Republic of Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korean Peninsula and sharing a land border with North Korea. Its western border is formed by the Yellow Sea, while its ea ...
and
East Germany East Germany, officially the German Democratic Republic (GDR; german: Deutsche Demokratische Republik, , DDR, ), was a country that existed from its creation on 7 October 1949 until its dissolution on 3 October 1990. In these years the state ...
, but the Korean masks were not suited for the faces of non-