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{{Short description|Protection from inhaling airborne pollutants and toxic gases}}
{{further|Elastomeric respirator|Gas mask canister}}
{{More citations needed|date=July 2024}}
{{Infobox regulated PPE
| image = Indiana Urban Search and Rescue Task Force 1 suits up for Vibrant Response 2014 140722-A-PC120-205.jpg
| caption = Two people wearing full-face [[elastomeric respirator]]s with gas mask canisters
}}
[[File:A World War I British gas hood c.1915.jpg|thumb|upright|A World War I British P Helmet, {{Circa|1915}}]]
[[File:Man wearing a Zelinsky-Kummant gas mask.jpg|thumb|Zelinsky–Kummant ''protivogaz'', designed in 1915, was one of the first modern-type full-head protection gas masks with a detachable filter and eyelet glasses, shown here worn by U.S. Army soldier ([[USAWC]] photo)]]
[[File:The British Army in France 1940 F2676.jpg|thumb|Indian muleteers and mule wearing gas masks, France, February 21, 1940]]
[[File:Gas mask MUA IMGP0157.jpg|thumb|upright|A Polish SzM-41M KF gas mask, used from the 1950s through to the 1980s]]
A '''gas mask''' is a piece of [[personal protective equipment]] used to protect the wearer from inhaling airborne [[pollutant]]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]]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. Gas masks only protect the user from ingesting or inhaling chemical agents, as well as preventing contact with the user's eyes (many chemical 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.<ref>{{cite web | title=Take a Moment to Breathe | date=8 August 2025 | url=https://www.thefirearmblog.com/blog/take-a-moment-to-breathe-44821828 }}</ref>

Airborne toxic materials may be gaseous (for example, [[chlorine]] or [[mustard gas]]), or particulates (such as [[biological warfare|biological agents]]). Many filters provide protection from both types.

Modern gas masks developed during World War I featured circular lenses made of [[glass]], [[mica]] or [[cellulose acetate]] 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)<ref>{{Cite book|last=Rumpf|first=Hans|title=Gasschutz}}</ref> 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{{clarify|which war?|date=July 2023}} (Austro-Hungarian 15M). Later, stronger [[polycarbonate]] 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.

==History and development==
===Early breathing devices===
According to ''[[Popular Mechanics]]'', "The common sponge was used in [[ancient Greece]] as a gas mask..."<ref>"''[https://books.google.com/books?id=0uMDAAAAMBAJ&pg=PA163-IA2 Popular Mechanics]''". January 1984. p. 163</ref> In 1785, [[Jean-François Pilâtre de Rozier]] invented a [[respirator]].

Primitive respirator examples were used by [[miner]]s and introduced by [[Alexander von Humboldt]] in 1799, when he worked as a mining engineer in [[Prussia]].<ref>{{Cite book | first=Alexander | last=Von Humboldt | year=1799 | title=Ueber die unterirdischen Gasarten und die Mittel, ihren Nachtheil zu vermindern: Ein Beytrag zur Physik der praktischen Bergbaukunde | publisher=Braunschweig, Friedrich Vieweg | url=https://books.google.com/books?id=LW1oAAAAcAAJ}}</ref> 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.<ref>{{cite web|title=The invention of the gas mask|publisher=Ian Taggart|url=http://www33.brinkster.com/iiiii/gasmask/page.html|url-status=dead|archive-url=https://web.archive.org/web/20130502145330/http://www33.brinkster.com/iiiii/gasmask/page.html|archive-date=May 2, 2013}}</ref> ''First Facts'' states that a "gas mask resembling the modern type" was patented by Lewis Phectic Haslett of [[Louisville, Kentucky]], who received a patent on June 12, 1849.<ref name="disu">{{cite book |editor1-last=Su|editor1-first=Di |title=Evolution in Reference and Information Services: The Impact of the Internet |last1=Drobnicki|first1=John A.|last2=Asaro|first2=Richard|chapter=Historical Fabrications on the Internet |publisher=Haworth Information Press|location=Binghamton, New York |year=2001 |page= 144|isbn= 978-0-7890-1723-9 |chapter-url=https://books.google.com/books?id=IvqbuSm4sHYC&q=gas+mask+patent+1849&pg=PA144}}</ref> U.S. patent #6,529<ref>{{Cite patent|title=Lung Protector|inventor-first=Lewis P.|inventor-last=Haslett|gdate=1849-06-12|country=US|number=6529A|inventorlink=Lewis_Haslett}}</ref> 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<ref name="Benson2010">{{cite book|author=Alvin K. Benson|title=Inventors and inventions|url=https://books.google.com/books?id=JqVZAAAAYAAJ|year=2010|publisher=Salem Press|isbn=978-1-58765-526-5}}</ref> and the physicist John Tyndall in the 1870s.<ref>{{cite book|title=The Environment and Its Effect Upon Man: Symposium Held at Harvard School of Public Health, August 24-August 29, 1936, as Part of Harvard University Tercentenary Celebration, 1636-1936|url=https://books.google.com/books?id=WYsaAAAAMAAJ|year=1937|publisher=Harvard School of Public Health}}</ref> 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.<ref>{{Cite book |last1=Gates |first1=Henry Louis Jr. |url=https://books.google.com/books?id=3dXw6gR2GgkC |title=African American Lives |last2=Higginbotham |first2=Evelyn Brooks |date=April 29, 2004 |publisher=Oxford University Press |isbn=9780199882861 |language=en |quote=}}</ref><ref name="pbs.org/wgbh/theymadeamerica2">{{cite web|url=https://www.pbs.org/wgbh/theymadeamerica/whomade/morgan_hi.html|title=Garrett Augustus Morgan|quote=He sold the hoods to the U.S. Navy, and the Army used them in World War I.|work=PBS Who Made America?}}</ref>

===World War I=== <!-- Excerpted in Respirator#History -->
[[Image:Bundesarchiv Bild 183-R52907, Mannschaft mit Gasmasken am Fla-MG.jpg|thumb|German soldiers with gas masks, 1916]]
The First World War brought about the first need for mass-produced gas masks on both sides because of [[Chemical weapons in World War I|extensive use of chemical weapons]]. The German army successfully used [[chemical weapon|poison gas]] for the first time against Allied troops at the [[Second Battle of Ypres]], Belgium on April 22, 1915.<ref>{{Cite web |title=First Usage of Poison Gas |url=https://www.theworldwar.org/learn/about-wwi/spotlight-first-usage-poison-gas |access-date=2024-08-18 |website=National WWI Museum and Memorial |language=en}}</ref> An immediate response was cotton wool wrapped in muslin, issued to the troops by May 1. This was followed by the [[Black Veil Respirator]], invented by [[John Scott Haldane]], which was a cotton pad soaked in an absorbent solution which was secured over the mouth using black cotton veiling.{{sfn|Wetherell|Mathers|2007|p=157}}

Seeking to improve on the Black Veil respirator, [[Cluny Macpherson (physician)|Cluny Macpherson]] created a mask made of chemical-absorbing fabric which fitted over the entire head: a {{cvt|50.5 x 48|cm|in}} canvas hood treated with chlorine-absorbing chemicals, and fitted with a transparent mica eyepiece.<ref name="Lefebure">{{cite book | url = https://archive.org/details/riddleofrhineche00lefe | title = The Riddle of the Rhine: Chemical Strategy in Peace and War | year=1999 |orig-date=1923 | publisher=University of Virginia Library (originally The Chemical Foundation Inc.) | author = Victor Lefebure | isbn = 0-585-23269-5 | url-access = registration }}</ref><ref name=rooms>{{cite web |url= http://www.rnr.therooms.ca/part3_a_soldiers_outfit.asp |title= Macpherson Gas Hood . Accession #980.222  |publisher=The Rooms Provincial Museum Archives (St. John's, NL) |access-date=August 5, 2017}}</ref> Macpherson presented his idea to the British War Office Anti-Gas Department on May 10, 1915; prototypes were developed soon after.{{sfn|Mayer-Maguire|Baker|2015}} 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.<ref name="RCS">{{Cite web |url=https://livesonline.rcseng.ac.uk/biogs/E005916b.htm |title=Biographical entry Macpherson, Cluny (1879 - 1966)  |website=livesonline.rcseng.ac.uk |access-date=April 22, 2018}}</ref> 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]], [[diphosgene]] and [[chloropicrin]]. In summer and autumn 1915, [[Edward Harrison (chemist)|Edward Harrison]], Bertram Lambert and John Sadd developed the Large Box Respirator.<ref name="gasmasknet">{{cite web|url-status = dead|archive-date=2008-07-09|archive-url=https://web.archive.org/web/20080709101905/http://www.gasmasks.net/database/uk/uk.htm|url = http://www.gasmasks.net/database/uk/uk.htm | title = The UK | work = The Gas Mask Database }}</ref>{{Better source needed|reason=The current source is insufficiently reliable ([[WP:NOTRS]]).|date=July 2024}} 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.{{Citation needed|date=July 2024}}

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]]s, [[chestnut]]s, [[horse-chestnut]]s, 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.<ref>''Once Worthless Things that have Suddenly Become of Value'', [[Popular Science]] monthly, December 1918, page 80, scanned by [https://books.google.com/books?id=EikDAAAAMBAJ&pg=PA80 Google Books]</ref>

The first effective filtering [[activated charcoal]] gas mask in the world was invented in 1915 by Russian chemist [[Nikolay Zelinsky]].<ref>{{cite book|last=Kozhevnikov|first=A B|title=Stalin's great science: the times and adventures of Soviet physicists|url=https://books.google.com/books?id=l1Ha_opwB68C|access-date=April 28, 2009|edition=illustrated, reprint|year=2004|publisher=Imperial College Press|isbn= 978-1-86094-419-2|pages=10–11}}</ref>

[[File:BunkArt-Horse-Gas-Mask.jpg|thumb|Gas mask for horses|alt=]]
[[Image:Soldaty 267 Duhovshinskogo polka.jpg|thumb|1916, Russian soldiers]]
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.<ref>[https://books.google.com/books?id=EikDAAAAMBAJ&pg=PA75 "Gas-Masks for Dogs / Dumb Heroes of the Fighting Front"], ''[[Popular Science]]'' monthly, December 1918, page 75, Scanned by Google Books</ref> 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.<ref>[https://books.google.com/books?id=LeADAAAAMBAJ&dq=Popular+Science+1930+plane+%22Popular+Mechanics%22&pg=PA75 "Gas Masks to Guard Horses and Dogs in War"] ''Popular Mechanics'', July 1934, bottom pg. 75</ref> 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.<ref name="ReferenceA">Pittsburgh Post-Gazette, November 30, 1960</ref>

===World War II===
[[File:Air Raid Precautions on the British Home Front- Anti-gas Instruction, c 1941 D3948.jpg|thumbnail|right|A British couple wearing gas masks in their home in 1941]]
{{anchor|WWII gas mask}}
The British Respirator, Anti-Gas (Light) was developed in 1943 by the British.<ref>{{Cite web|url=https://www.iwm.org.uk/collections/item/object/30016346|title = Respirator, Anti-Gas (Light) MKII: With Haversack Carrier & contents}}</ref> 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.{{Citation needed|date=April 2023}}

=== 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]] 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 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 ([[chemical, biological, radiological, and nuclear|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]]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.{{citation needed|date=March 2017}}

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.).

[[File:Chemical weapon1.jpg|thumb|Iranian soldier wearing a US M17 protective mask on the frontline of the [[Iran–Iraq War]]]]
During the [[Iran–Iraq War]] (1980–88), Iraq developed [[Iraqi chemical weapons program|its chemical weapons program]] with the help of European countries such as Germany and France<ref>{{Cite web|title=Iraqi Scientist Reports on German, Other Help for Iraq Chemical Weapons Program|url=https://fas.org/nuke/guide/iraq/cw/az120103.html|access-date=2021-06-28|website=fas.org}}</ref> 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]] and [[East Germany]], but the Korean masks were not suited for the faces of non-[[East Asian people]], the filter lasted for only 15 minutes, and the 5,000 masks bought from East Germany proved to be not gas masks but spray-painting goggles. As late as 1986, Iranian diplomats still travelled in Europe to buy [[active charcoal]] and models of filters to produce defensive gear domestically. In April 1988, Iran started domestic production of gas masks by the Iran Yasa factories.<ref>{{Cite web|url=http://cns.miis.edu/archive/cns/programs/dc/briefs/030701.htm |title=Iranian Use of Chemical Weapons: A Critical Analysis of Past Allegations |last=Zanders |first=Jean Pascal |date=March 7, 2001 |website=CNS Briefings |publisher=James Martin Center for Nonproliferation Studies |access-date=March 27, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20150320222016/http://cns.miis.edu/archive/cns/programs/dc/briefs/030701.htm |archive-date=March 20, 2015 }}</ref>

[[File:Viktor Billa Oborona pionerov.jpg|thumb|right|200px|[[Pioneer movement|Pioneers]] in gas masks. [[USSR]], 1937]]

==Principles of construction==
[[Absorption (chemistry)|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 [[chemical reaction|reaction]] may take place, it is not necessary; the method may work by attractive [[electric charge|charges]]. For example, if the target particles are positively charged, a negatively charged substrate may be used. Examples of substrates include [[activated carbon]], and [[zeolite]]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.

<gallery>
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 mask]]s
</gallery>

===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.<ref>{{cite web |last1=Speakerman |first1=Jay |title=The Deadly Truth: Why the WW2 Gas Mask Was Dangerous Equipment to Carry |url=https://www.mirasafety.com/blogs/news/ww2-gas-mask-health-risks |website=www.mirasafety.com |date=17 March 2025 |publisher=MIRA Safety |access-date=18 June 2025}}</ref>

Some World War II and Soviet Cold War gas mask filters contained [[chrysotile asbestos]] or [[Riebeckite#Crocidolite (fibrous riebeckite)|crocidolite asbestos]].<ref>{{Cite web|title=Porton Down report on the presence of asbestos in World War II respirator canisters|url=http://ibasecretariat.org/porton_down_rep_1989.pdf |archive-url=https://web.archive.org/web/20190502224759/http://ibasecretariat.org/porton_down_rep_1989.pdf |archive-date=2019-05-02 |url-status=live|page=2 (summary)}}</ref><ref>{{Cite news| last = Burns| first = Judith| title = Ban wartime gas masks, schools told| work = BBC News| access-date = August 21, 2018| date = May 13, 2014| url = https://www.bbc.com/news/education-27391955}}</ref><ref>{{Cite book| publisher = Springer Science & Business Media| isbn = 978-1-4612-2496-9| last1 = Dail| first1 = David H.| last2 = Hammar| first2 = Samuel P.| last3 = Colby| first3 = Thomas V.| title = Pulmonary Pathology — Tumors| date = December 6, 2012 |url=https://books.google.com/books?id=wSgyBwAAQBAJ&pg=PT1005}}</ref> 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&nbsp;mm connections are a more recent design. Rubber degrades with time, so boxed unused "modern type" masks can be [[ozone cracking|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]].<ref>{{Cite web|title=OPERATOR'S MANUAL
|url=http://chemicaldragon.com/yahoo_site_admin/assets/docs/TM_3-4240-342-10.12652555.pdf|access-date=2022-02-05|archive-url=https://web.archive.org/web/20160429130940/http://chemicaldragon.com/yahoo_site_admin/assets/docs/TM_3-4240-342-10.12652555.pdf|archive-date=2016-04-29}}</ref>

=== Modern filter classification ===
{{See also|Cartridge (respirator)#Classification and marking of cartridges}}
The filter is selected according to the toxic compound.<ref name=draeger>{{cite web|url=http://www.draeger.com/media/10/01/09/10010967/guide_for_selection_and_use_of_filtering_devices_9045782_en.pdf|title=Guide for selection and use of filtering devices|publisher=draeger.com|access-date=February 22, 2013|archive-url=https://web.archive.org/web/20120526013417/http://www.draeger.com/media/10/01/09/10010967/guide_for_selection_and_use_of_filtering_devices_9045782_en.pdf|archive-date=May 26, 2012|url-status=dead}}</ref> Each filter type protects against a particular hazard and is color-coded:

{| class=wikitable
|+Filter types
|-
! EU Class, color !! US color<ref name=osha_2011>{{cite web |title=OSHA Bulletin: General Respiratory Protection Guidance for Employers and Workers |url=https://www.osha.gov/dts/shib/respiratory_protection_bulletin_2011.html |website=Occupational Safety and Health Administration}}</ref>!! Hazard
|-
| AX, brown || rowspan=2| black || Low-boiling (≤65&nbsp;°C) organic compounds
|-
| A, brown || High-boiling (>65&nbsp;°C) organic compounds
|-
| B, grey || (many) || Inorganic gases ([[hydrogen sulfide]], [[chlorine]], [[hydrogen cyanide]])
|-
| E, yellow || white || Acidic gases ([[Sulfur dioxide]] and [[hydrogen chloride]])
|-
| K, green || green || [[Ammonia]] and [[amine]]s
|-
| CO, black || blue || [[Carbon monoxide]]
|-
| Hg, red || {{N/A}} || [[mercury (element)|Mercury]] vapor
|-
| R(eactor), orange || magenta || Radioactive particles ([[iodine]] and [[methyl iodide]])
|-
| P, white || purple, orange, or teal || Particles
|}

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.<ref name=draeger/> In the US, only the particle part is further classified by [[NIOSH air filtration rating]]s.<ref name=osha_2011/>

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.<ref name=draeger/> A2B2E2K2-P3 is the highest rating of filter available.{{when|date=April 2020}} An entirely different "multi/CBRN" filter class with an olive color is used in the US.<ref name=osha_2011/>

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]]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 ==
[[File:Monmouth Regimental Museum - QRpedia 5.JPG|thumb|A 1939 Second World War-era baby's gas mask in [[Monmouth Regimental Museum]]. This design covered the whole of the baby except for its legs.]]
[[File:Aalsmeer_een_medewerker_van_kwekerij_Baardse_met_gasmasker_tegen_het_inademen_v,_Bestanddeelnr_191-0038.jpg|thumb|A worker in a [[plant nursery]] wears a respirator to protect against the insecticides sprayed in the greenhouses, 1930.]]
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]] are often used as innocuous challenge agents. In the military, [[teargas]]es such as [[CN gas|CN]], [[CS gas|CS]], and [[stannic chloride]] in a chamber may be used to give the users confidence in the efficacy of the mask.<ref>{{Cite web |url=http://www.af.mil/shared/media/epubs/AFMAN32-4006.pdf |title=AF M32-4006 - Nuclear, biological, and chemical (nbc) mask fit and liquid hazard simulant training |access-date=July 9, 2010 |archive-url=https://web.archive.org/web/20121020175705/http://www.af.mil/shared/media/epubs/AFMAN32-4006.pdf |archive-date=October 20, 2012 |url-status=dead }}</ref>

{{Further| MOPP (protective gear) | NBC suit}}

== 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#Toxicity|carbon dioxide]] may exceed its [[Occupational exposure limit|OELs]] (0.5% by volume/9&nbsp;grammes per cubic metre for an eight-hour shift; 1.4%/27 grammes per m<sup>3</sup> for 15 minutes' exposure)<ref>{{cite book |editor-last1=Popova |editor-first1=Anna |title=Hygienic standard 2.2.5.3532-18.Occupational exposure limits for toxic substances in workplace air [ГН 2.2.5.3532-18 Предельно допустимые концентрации (ПДК) вредных веществ в воздухе рабочей зоны] |year=2018 |publisher=Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing |chapter=Substance #2138 Carbon dioxide |location=Moscow |language=ru |pages=170 |url=https://www.rospotrebnadzor.ru/documents/details.php?ELEMENT_ID=9967&sphrase_id=2681452 |access-date=2020-10-01 |archive-date=2022-03-11 |archive-url=https://web.archive.org/web/20220311073942/https://www.rospotrebnadzor.ru/documents/details.php?ELEMENT_ID=9967&sphrase_id=2681452 |url-status=dead }}</ref> by a factor of many times: for gas masks and [[elastomeric respirator]]s, up to 2.6%<ref>Mean values for several models; some models may provide a stronger exposure to carbon dioxide.</ref>);<ref name="Sinkule-2003">{{cite book |last1=Sinkule |first1=E. |last2=Turner |first2=N. |last3=Hota |first3=S. |title=American Industrial Hygiene Conference and Exposition, May 10-15, 2003 |date=2003 |publisher=American Industrial Hygiene Association |location=Dallas, Texas |page=54 |url=https://www.cdc.gov/niosh/nioshtic-2/20022781.html |language=en |chapter=Automated breathing and metabolic simulator (ABMS) CO<sub>2</sub> test for powered and non-powered air-purifying respirators, airline respirators, and gas mask}} [https://www.researchgate.net/publication/307855799_Sinkule_Turner_Hota_AIHce_abstracts_p54_2003_Dallas_TX copy]</ref> and in case of long-term use, [[headache]],<ref name="Lim-2006">{{cite journal |first1=E.C.H. |last1=Lim |first2=R.C.S. |last2=Seet |first3=K.-H. |last3=Lee |first4=E.P.V. |last4=Wilder-Smith |first5=B.Y.S. |last5=Chuah |first6=B.K.C. |last6=Ong |title=Headaches and the N95 face-mask amongst healthcare providers |journal=Acta Neurologica Scandinavica |date=2006 |volume=113 |issue=3 |pages=199–202 |doi=10.1111/j.1600-0404.2005.00560.x |pmid=16441251 |url= |publisher=John Wiley & Sons |pmc=7159726 |doi-access=free |language=en |issn=0001-6314}}</ref> [[dermatitis]] and [[acne]]<ref name="Goh-2006">{{cite journal |author1=Chris C.I. Foo|author2=Anthony T.J. Goon|author3=Yung-Hian Leow|author4=Chee-Leok Goh |title=Adverse skin reactions to personal protective equipment against severe acute respiratory syndrome – a descriptive study in Singapore |doi-access=free |journal=Contact Dermatitis |date=2006 |volume=55 |issue=5 |pages=291–294 |doi=10.1111/j.1600-0536.2006.00953.x |url= |publisher=John Wiley & Sons |pmid=17026695 |pmc=7162267 |language=en |issn=0105-1873}}</ref> may appear. The [[Health and Safety Executive|UK HSE]] textbook recommends limiting the use of respirators without air supply (that is, not [[Powered air-purifying respirator|PAPR]]) to one hour.<ref name="HSE-2013">{{cite book |last1=The Health and Safety Executive |title=Respiratory protective equipment at work. A practical guide |date=2013 |publisher=Crown |isbn=978-0-71766-454-2 |pages=59 |edition=4 |url=http://www.hse.gov.uk/pubns/books/hsg53.htm |series=HSG53|access-date=June 10, 2018 }}</ref>

==Reaction and exchange==
{{Main|Chemical cartridge#Detection of end of service life}}
{{Unreferenced section|date=October 2017}}

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]]s. These can be created with different groups of [[atom]]s (usually called [[functional group]]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 [[Chemical cartridge#Detection of end of service life|replace the filter device in the mask]], or use a new mask.

<gallery>
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 (World War I)|Western Front]] and [[Eastern Front (World War I)|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
</gallery>

==See also==
* [[Respirator Assigned Protection Factors|Assigned Protection Factors]]
* [[Cartridges and canisters of air-purifying respirators]]
* [[GP-7 gas mask]]
* [[GP-5 gas mask]]
* [[Hopcalite]]
* [[M2 Gas Mask]]
* [[M40 Field Protective Mask]]
* [[M50 joint service general purpose mask]]
* [[C-4 Protective Mask]]
* [[NBC suit]]
* [[PH helmet]]
* [[Plague doctor costume|Plague doctor's outfit]]
* [[Respirator]]
* [[Respirator fit test]]
* [[Respirators testing in the workplaces]]
* [[Respirator assigned protection factors]]
* [[Smoke hood]]

{{Clear}}

==Notes==
{{Reflist}}

==Bibliography==
{{refbegin |colwidth=30em}}
* {{citation |last1=Wetherell |first1=Anthony |last2=Mathers |first2=George |year=2007 |contribution=Respiratory Protection |editor-last=Marrs |editor-first=Timothy |editor2-last=Maynard |editor2-first=Robert |editor3-last=Sidell |editor3-first=Frederick |title=Chemical Warfare Agents: Toxicology and Treatment|location=New York |publisher=Wiley |pages=157–174 |isbn=978-0470013595}}
* {{citation |last1=Mayer-Maguire |first1=Thomas |last2=Baker |first2=Brian |year=2015 |title=British Military Respirators and Anti-Gas Equipment of the Two World Wars |publisher=Crowood}}
{{refend}}

==Further reading==
{{wikisource|What You Should Know in Deciding Whether to Buy Escape Hoods, Gas Masks, or Other Respirators for Preparedness at Home and Work|What You Should Know in Deciding Whether to Buy Escape Hoods, Gas Masks, or Other Respirators for Preparedness at Home and Work (2003)}}
{{refbegin}}
* [https://www.cdc.gov/niosh/npptl/multivapor/Tutorials/MultiVapor213Tutorial-508.pdf NIOSH MultiVapor manual], [https://www.cdc.gov/niosh/npptl/multivapor/Tutorials/MultiVapor213Tutorial.wmv External video]
** {{cite journal | title=Correlating and Extrapolating Air-Purifying Respirator Cartridge Breakthrough Times--A Review | url=https://gerryowood.com/uploads/3/4/7/2/34729297/jsrp2015.pdf | last=Wood | first=Jerry O. | journal=Journal of the International Society for Respiratory Protection | volume=32 | issue=23–26 | date=2015 }}
** {{cite journal | title=Testing Air-Purifying Chemical Respirator Cartridges: A Review of Options | url=https://gerryowood.com/uploads/3/4/7/2/34729297/jisrp_34_no._1__2017.docx | last=Wood | first=Jerry O. | journal=Journal of the International Society for Respiratory Protection | volume=34 | issue=1 | date=2017 }}
{{refend}}
{{clear}}

==External links==
{{Commons}}
* [http://science.howstuffworks.com/gas-mask.htm/printable How Stuff Works - Gas Masks] Science.com
* [http://inventors.about.com/od/gstartinventions/a/gasmask.htm The History of Gas Masks] {{Webarchive|url=https://web.archive.org/web/20200326143451/https://www.thoughtco.com/history-of-gas-masks-1991844 |date=2020-03-26 }} inventors.about.com, About, Inc. updated March 3, 2024  12:47
* [https://www.cdc.gov/niosh/npptl/topics/respirators/factsheets/respfact.html Respirator Fact Sheet]
* [https://www.cdc.gov/niosh/npptl/topics/respirators/cel/default.html NIOSH NPPTL]
* [https://www.cdc.gov/niosh/npptl/multivapor/multivapor.html NIOSH MultiVapor breakthrough concentration program]
** [https://gerryowood.com/service-life-estimation-computer-programs.html#/ NIOSH GasRemove (beta)]
* [https://www.osha.gov/etools/respiratory-protection/change-schedules/math-model OSHA math model tool for replacement of chemical cartridges]
{{Breathing apparatus|industrial}}
{{Gas masks}}
{{Authority control}}

{{DEFAULTSORT:Gas Mask}}
[[Category:American inventions]]
[[Category:British inventions]]
[[Category:Russian inventions]]
[[Category:Science and technology in the United Kingdom]]
[[Category:Military personal equipment]]
[[Category:1914 introductions]]
[[Category:Riot control equipment]]
[[Category:Gas masks|*Main]]
[[Category:Respirators]]