A respirator cartridge or gas mask 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 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. PDF (On Russian 2023)
Purification methods
Absorption
Capturing noxious gases may be accomplished by sorbents. These materials (activated carbon, , 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. Gradually, the sorbent 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. Conference listing
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, 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, 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 hopcalite 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 and canisters
Combined, or multi-gas canisters and cartridges, protect from harmful gases by using multiple sorbents or catalysts. An example is the ASZM-TEDA Carbon canister 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).
Classification and marking
Cartridge selection comes after assessing the atmosphere. NIOSH guides cartridge (and canister) choice in the US along with manufacturer recommendations.
United States
European Union and Russia
In the European Union (EU) and the Russian Federation (RF), manufacturers can certify cartridges intended for cleaning the air of various gaseous contaminants. The codes are covered by EN 14387, additionally, particulate codes P1, P2, and P3 are used. For example, A1P2 is the code for commonly used filters in industry and agriculture that provide protection against A-type gases, commonly occurring particulates, and other organic particulates. Harmful substances Marking Color Low sorbent capacity Medium sorbent capacity Large sorbent capacity Organic gases and vapors with boiling point above 65 °C recommended by the manufacturer А Brown A1 A2 A3 Inorganic gases and vapors, with the exception of carbon monoxide, recommended by the manufacturer В Grey В1 В2 В3 Sulphur dioxide and other acid gases and vapors recommended by the manufacturer E Yellow Е1 Е2 Е3 Ammonia and its organic derivatives recommended by the manufacturer K Green К1 К2 К3 Organic compounds with low boiling temperature (<65°С) recommended by the manufacturer AX Green AX Particular gases specified by the manufacturer SX Violet SX Nitric oxide NO (NO2) NO Blue and white NO Cartridges AX, SX, and NO do not distinguish on the sorption capacity (as in the US) when they are classified and certified.
If the cartridge is designed to protect from several different types of harmful gases, the label will list all designations in order. For example: A2B1, color - brown and grey.
Other jurisdictions that use this style of classification include Australia/New Zealand (AS/NZS 1716:2012) and China (GB 2890:2009).
Detection of end of service life
The service lives of all types of cartridges are limited, therefore, the employer is obliged to replace them in a timely manner.
Old methods
Subjective reactions of users' sensory systems The use of cartridges in the contaminated atmosphere leads to saturation of the sorbent (or the dryer, when using catalysts). Once fully saturated, concentration of harmful gases in the purified air gradually increases. The presence of harmful gases in the inhaled air can lead to a reaction in a user's sensory system: odor, taste, irritation of the respiratory system, dizziness, headaches, and other health impairments up to loss of consciousness and death.
These signs (known in the US as "warning properties" - p. 28) indicate that one must leave the polluted workplace area, and replace the cartridge with a new one. This can also be a symptom of a loose fit of the mask to one's face, and the leakage of unfiltered air through the gaps between the mask and the face. Historically, this method is the oldest.
The advantages of this method – if harmful gases have warning properties at concentrations less than 1 PEL, the replacement will be produced on time (in most cases, at least); the application of this method does not require the use of special cartridges (more expensive) and accessories; replacement happens when one needs to do it – after the sorbent saturation, and without any calculations; the sorption capacity of the cartridges is fully expired (which reduces costs for respiratory protection).
The disadvantage of this method is that some harmful gases have no warning properties. For example, there is a list of over 500 harmful gases in the Respirator Selection Guide. Over 60 of them have no warning properties, and there is no such information for over 100 of them. This can lead to breathing air with an excess harmful gas concentration in some cases, if one uses warning properties to replace cartridges.
Gases and vapors (CAS) Short term PEL, mg/m3 Odor thresholds, mg/m3 3M Russia Maximum and minimum Heptane (142–82–5) 900 40.7 3000 - 1.7 Methyl acetate (79–20–9) 100 19 8628 - 0.5 Dichloromethane (75–09–2) 100 3.41 1530 - 4.1 Tetrahydrofuran (109–99–9) 100 11.39 180 - 0.27 Cyclohexane (110–82–7) 80 293 2700 - 1.8 Trichloroethene (79–01–6) 30 7.43 900 - 2.5 Tetrachlorethylene (127–18–4) 30 42.53 480 - 8.1 2-Ethoxyethanol (110–80–5) 30 4.57 180 - 1.1 Carbon tetrachloride (56–23–5) 20 260.3 3700 - 10.6 Chloroform (67–66–3) 10 61 6900 - 0.5 Benzene (71–43–2) 15 29.7 1000 - 2.5 1,1,2,2-Tetrachloroethane (79–34–5) 5 1.46 50 - 1.6 Allyl alcohol (107–18–6) 2 1.16 83 - 1.2 Epichlorohydrin (106–89–8) 2 3.59 46 - 0.3 Hydrocyanic acid (74–90–8) 0.3 0.72 6 - 0.01 Phosphine (7803–51–2) 0.1 0.198 7 - 0.014 Chlorine (7782–50–5) 1 no information 14,3 - 0,06 According to the ICHS, all listed substances in the table cannot be reliably detected by smell at dangerous concentrations. On the other hand, all publications with information only about average odor perception thresholds can partly misinform the reader, since they create the impression that the thresholds are stable and constant.
If the threshold odor of Benzene is 20 PEL; and if its concentration is only 10 PEL, one cannot timely change cartridges by using smell - they could be "used" forever, but they cannot protect forever.
The practice has shown that the presence of warning properties does not always lead to timely cartridge replacement. A 1983 study showed that on average 95% of a group of people have an individual threshold of olfactory sensitivity in the range of from 1/16 to 16 from the mean. This means that 2.5% of people will not be able to smell harmful gases at a concentration 16 times greater than the average threshold of perception of a smell. The threshold of sensitivity of different people can vary by two orders of magnitude. That is, 15% of people do not smell at concentrations four times higher than the sensitivity threshold. The value of threshold smell greatly depends on how much attention people pay to it, and on their health status.
The sensitivity may be reduced, for example, due to colds and other ailments. It turns out that a worker's ability to detect smell also depends on the nature of the work to be performed — if it requires concentration, a user may not react to the smell. Prolonged exposure to harmful gases (for example, hydrogen sulfide) at low concentrations can create olfactory fatigue which reduces sensitivity. In a group of workers, the average styrene odor threshold increased by an order of magnitude due to adaptation. However, the perception of odors of other substances did not change. And the workers could mistakenly believe that their olfactory organ remained sensitive to styrene too.
This was the reason for the ban of this method of cartridge replacement in the US since 1996 .
Mass increase
Filters to protect workers from carbon monoxide cartridges often use the catalyst hopcalite. This catalyst does not change its properties over time when it is being used, but when it moistens, the degree of protection may be significantly reduced. Because water vapor is always present in the air, the polluted air is dehumidified in the cartridge (for use of the catalyst). Since the mass of water vapor in the polluted air is greater than the mass of harmful gases, trapping moisture from the air leads to a significantly higher increase in the mass of cartridges than the trapping gases. This is a substantial difference, and it can be used to determine whether to continue to use gas cartridges further without replacement. The cartridge is weighed, and a decision can be made based on the magnitude of increase of its mass.
Other methods Certain documents described Soviet cartridges (model "Г"), as being designed to protect from mercury. Their service life was limited to 100 hours of use (cartridges without particle filter), or 60 hours of use (cartridges with particle filter), after which it was necessary to replace the cartridge with a new one.