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The Czech CM-4 was designed for civilian use, but several modifications of this mask made it suitable not only for civilians, but also for civil workers, police, military, and even industrial use. The advancements of this mask led to the Czech OM10 which is widely popular due to its low price, high availability and features that many consider essential such as a drinking tube.
Three main types of CM-4 gas masks existed - the standard CM-4, the upgraded CM-4M, and the CM-4K which was meant to be used in industrial environments. All had similar designs, but with minor differences.
The CM-4 is the basic model that includes a double exhale valve, a five-point head harness, a neck strap, and uses the GOST 40mm gas mask thread allowing the mask to be compatible with most east-bloc filters. Protection is guaranteed in a temperature range between -30°C and +50°C. The mask, on average, weighs approximately 400 grams.
The CM-4M also included a drinking tube which comes in handy if the user has to stay in a contaminated area for long periods of time.
The CM-4K added a hose with a filter attached to the end as opposed to the filter being directly attached to the mask. This better suited workers in industrial conditions.
(CM-4 is using filter MOF-4)
As an essential utility component part of the DK-62, DK-88, DM-1, CM3/3h, CM-3, CM-4, and CM-5 individual protection equipment these filter canisters provide respiratory protection against consequences of chemical warfare agents, toxic substances, radioactive particles, and biological warfare agents.
Each filter canister consists of an aluminum alloy casing which contains a filtration part ( filter-paper) and a sorption part (activated carbon absorbent). Each filter canister is equipped with a polyethylene seal and cover lid.
Weight of MOF-2 and MOF-5…………..............................260 g
Weight of MOF-4…………..............................from 240 to 260 g
Tightness- penetration coefficient MOF-2…..………..…0.007%
Tightness- penetration coefficient MOF-2 and MOF-5...0.0001%
Pressure loss at airflow 30 l/min:
MOF-2 190 Pa
MOF-4 170 Pa
MOF-5 150 Pa
Sorption capacities in grams:
MOF-2 MOF-4 MOF-5
Chloropicrin 3 3 8
Hydrogen Cyanide 3.7 3.7 3.7
Cyanogen Chloride 1.8 2 2
Phosgene 7.5 7.5 7.5
So to end about filters:
Filters are supposedly safe, mask even creates a good seal with NATO 40mm filters, but also with Soviet ones (what is exciting, because Czechoslovakia was in Warsaw pact). But if you still are worried about original filters, as mentioned, you can use NATO ones.