Chemical cartridge

(Redirected from Cartridges and canisters of air-purifying respirators)

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This article is about the type of respirator filter.

A respirator **cartridge** or **canister** is a type of filter that removes gases, volatile organic compounds (VOCs), and other vapors from the air through adsorption, absorption, or chemisorption. It is one of two basic types of filters used by air-purifying respirators. The other is a mechanical filter, which removes only particulates. Hybrid filters combine the two.

Workplace air that is polluted with fine particulate matter or noxious gases but that contains enough oxygen (in the US, this is ruled to be a concentration above 19.5%; in the Russian Federation, above 18%, can be rendered safe via air-purifying respirators. Cartridges are of different types and must be chosen correctly and replaced on an appropriate schedule.

## Purification methods

### Absorption

Capturing noxious gases may be accomplished by sorbents. These materials (activated carbon, aluminum oxide, zeolite, etc.) have a large specific surface area and can absorb many gases. Typically, such sorbents are in the form of granules and fill the cartridge. Contaminated air travels through the cartridge's bed of sorbent granules. Movable harmful gas molecules collide with the surface of the sorbent and remain therein. The sorbent gradually saturates and loses its ability to capture pollutants. The bond strength between captured molecules and the sorbent is small, and molecules can separate from the sorbent and return to the air. The sorbent's ability to capture gases depends on the properties of the gases and their concentrations, including air temperature and relative humidity.

### Chemisorption

Chemisorption utilizes a chemical reaction between the gas and the absorber. The ability of some harmful gases to react chemically with other substances can be used to capture them. Creating strong links between gas molecules and a sorbent may allow repeated use of a canister if it has enough unsaturated sorbent. Copper salts, for example, can form complex compounds with ammonia. A mixture of copper ions (+2), zinc carbonate, and TEDA can detoxify hydrogen cyanide. By saturating activated carbon with chemicals, chemisorption can be used to help the material make stronger ties with molecules of trapped gases and improve the capture of harmful gases. Saturation of iodine improves mercury capture, a saturation of metal salts improves ammonia capture, and saturation of metal oxides improves acid gas capture.

### Catalytic decomposition

Some harmful gases can be neutralized through catalytic oxidation. A hoplite can oxidize toxic carbon monoxide (CO) into harmless carbon dioxide (CO2). The effectiveness of this catalyst strongly decreases as relative humidity increases. Therefore, desiccants are often added. Air always contains water vapor, and after saturation of the desiccant, the catalyst ceases to function.

### Combined cartridges

Combined, or multi-gas cartridges protect from harmful gases by using multiple sorbents or catalysts. An example is *ASZM-TEDA Carbon* used in CBRN masks by the US Army. This is a form of activated carbon saturated with copper, zinc, silver, and molybdenum compounds, as well as with triethylenediamine (TEDA).

Information was found on Wikipedia.