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A gas mask is a piece of personal protective equipment used to protect the wearer from inhaling airborne 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 , 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.
Airborne toxic materials may be gaseous (for example, chlorine or mustard gas), or particulates (such as 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) became more popular, and alongside plain cellulose acetate they became the standard into the 1930s. Panoramic lenses were not popular until the 1930s. 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.
Primitive respirator examples were used by and introduced by Alexander von Humboldt in 1799, when he worked as a mining engineer in Prussia. 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, who received a patent on June 12, 1849. (2026). 9780789017239, Haworth Information Press. ISBN 9780789017239 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.
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.Victor Lefebure (1999). 9780585232690, University of Virginia Library (originally The Chemical Foundation Inc.). . ISBN 9780585232690 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, diphosgene and chloropicrin. In summer and autumn 1915, Edward Harrison, Bertram Lambert and John Sadd developed the Large Box Respirator. 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 , , , 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. Once Worthless Things that have Suddenly Become of Value, Popular Science monthly, December 1918, page 80, scanned by Google Books
The first effective filtering activated charcoal 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. "Gas-Masks for Dogs / Dumb Heroes of the Fighting Front", Popular Science monthly, December 1918, page 75, Scanned by Google Books 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. "Gas Masks to Guard Horses and Dogs in War" Popular Mechanics, July 1934, bottom pg. 75 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.Pittsburgh Post-Gazette, November 30, 1960
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 (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 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.
Some World War II and Soviet Cold War gas mask filters contained chrysotile asbestos or crocidolite asbestos. 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 ozone cracking 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.
| + Filter types | ||
| AX, brown | Black | Low-boiling (≤65 °C) organic compounds |
| A, brown | High-boiling (>65 °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 |
| CO, black | Blue | Carbon monoxide |
| Mercury vapor | ||
| R(eactor), orange | Magenta | Radioactive particles (iodine and methyl iodide) |
| P, white | Purple, Orange, 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. 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 , 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.
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, such as CN gas, CS gas, and stannic chloride in a chamber may be used to give the users confidence in the efficacy of the mask.
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:
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.
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 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 respirators, up to 2.6%Mean values for several models; some models may provide a stronger exposure to carbon dioxide.); copy and in case of long-term use, headache, dermatitis and acne 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 . These can be created with different groups of (usually called ) 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.
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