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Emergency Manager
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Discussion Starter · #1 · (Edited)
QUESTION:I just bought a respirator/gas mask. Are the filters any good? How long will the filter last if I need to use it?



Storage Life

Provided they are properly sealed, the filters are good until the expiration printed on the packaging. This may be 1 year, 5 years, 10 years or even longer. Beware of companies claiming 20+ year shelf-lives, especially if the filter isn’t vacuum sealed. If the filters are surplus filters without an expiration date or the filters are not sealed in the original manufacturer's air-tight container or packaging, regardless of what the seller claims, they should be treated as “expired”.

After the expiration date, or if they are opened for any reason, the filters should be discarded and replaced. Contrary to popular opinion, gas mask filters are not simply activated charcoal sandwiched by filter medium. These filters also contain catalytic materials that react with some chemical vapors to neutralize them. Those materials may be in a separate layer in the canister, or the activated charcoal may be impregnated with these catalysts. Once exposed to air, these materials degrade and lose their protective properties.

Service Life

How long a filter cartridge will last is a complex problem and if you’re looking for a short, definitive answer, I’m afraid there isn’t one. There are no “rules of thumb” for how long a layperson can use a respirator in an emergency setting. In the professional world, the service life of respirator cartridges/filters is based on the concentration of the agent being filtered. It is highly unlikely a layperson will have access to the necessary tools or information to make an accurate measurement or estimate of the concentration. If you’re unable to determine the concentration, there’s no way to determine how long the filter can be expected to provide adequate protection. This is the number one reason laypersons should only use gas masks and respirators for escape. It’s also why virtually every guide, standard, or manual recommends the use of SCBA when the agent or concentration is not known.

The NIOSH CBRN Respiratory Protection Handbook recommends that NIOSH approved APRs (Air Purifying Respirators) be used for no longer than 8 hours once exposure to chemical warfare agents has started. If the respirator is exposed to liquid droplets, that time drops to two (2) hours. Note, that this doesn’t mean a respirator filter will last the full 8 hours, or even the full 2 hours. These times are for APR or PAPR devices. SCBA is actually less (6 hours). As with other hazardous chemicals, how well and how long a filter performs against chemical warfare agents is based on the agent and the concentration of that agent. Under high concentrations, the agent will break through the filter medium much faster than the times referenced above. Since some threats are odorless/tasteless at dangerous concentrations or may otherwise damage the sense of smell, you cannot rely on your sense of smell to tell you when you need a new filter.

Particulate-only Environments

Fortunately, most of the CBRN equation is composed of particulate agents. CS (Tear Gas), radioactive fallout (radioactive vapors and gasses excepted) and biological agents are all classified as particulates. Using a particulate filter (N95, N99, R99, P100, etc) in these environments doesn’t degrade the filter in the manner that a chemical environment degrades a filter. The particulates become trapped on or in the filter medium. Because of this, particulate filters don’t have an established service life. Instead, it is recommended that “All filters should be replaced whenever they are damaged, soiled, or causing noticeably increased breathing resistance (e.g., causing discomfort to the wearer).” How long that takes depends on how much “dust” is in the air. Keep in mind that the filter will become “hazardous” as you use it, so use caution when removing your mask or changing cartridges to prevent self-contamination.

Final Thoughts and Opinions

Remember, respirators do not provide you with oxygen, and will not protect you from environments where the oxygen has been depleted or displaced by other gasses. Thanks to charliemeyer007 for reminding me of this important caveat to respirator use. Many filter cartridges also do not filter combustion gasses like carbon monoxide. These gasses require special catalytic agents which convert the CO into CO2.

As a lay person, if you’re facing a CBRN environment and are using a respirator for anything other than to escape to a safe/safer location, you’re wrong. Contrary to internet wisdom, a respirator doesn’t give you the ability to penetrate or stay in a hazardous area. Donning your chem gear and a mask to go out and scavenge, or otherwise explore or otherwise exploit locations that unprotected individuals can’t, is the stuff of Hollywood and video game fantasy. In reality, these actions can get you killed in a CBRN environment. Especially where chemical agents are involved.


References and Related Reading

NIOSH [2018] Chemical, Biological, Radiological, and Nuclear (CBRN) Respiratory Protection Handbook. Retrieved From:
https://doi.org/10.26616/NIOSHPUB2018166

US Department of the Army. [2018] Pamphlet 385–61 Safety Toxic Chemical Agent Safety Standards. Retrieved From:
https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/ARN12692_PAM385-61_WEB_FINALL.pdf

NIOSH [2005] Interim Guidance on the Use of Chemical, Biological, Radiological and Nuclear (CBRN) Full Facepiece, Air-Purifying Respirators/Gas Masks Certified Under 42 CFR Part 84. Retrieved From:
https://www.cdc.gov/niosh/npptl/guidancedocs/interapr070805.html

NIOSH [1996] NIOSH Publication Number 96-101 Guide to the Selection and Use of Particulate Respirators. Retrieved From:
https://www.cdc.gov/niosh/docs/96-101/default.html

NRC [2001] Manual of Respiratory Protection Against Airborne Radioactive Material (NUREG/CR-0041, Revision 1). Retrieved From:
https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr0041/

 

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reluctant sinner
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I'd add one tip. Respirators at best filter out the bad stuff - however there still needs to be enough oxygen in the air to keep you alive. Confined entry places can be dangerous, even low lying areas can have normal air displaced.

Lots of bad stuff can be absorbed threw your skin.
 

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Emergency Manager
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Discussion Starter · #3 ·
I'd add one tip. Respirators at best filter out the bad stuff - however there still needs to be enough oxygen in the air to keep you alive. Confined entry places can be dangerous, even low lying areas can have normal air displaced.

Lots of bad stuff can be absorbed threw your skin.
Thank you for reminding me about that. I meant to address it and then promptly forgot. Absorption of chemicals through the skin is an important point too.
 

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I was the NBC NCO at the 56FA CMD in Germany back in the late 1980's and I remember the Army putting out a service bulletin regarding the filter cartridges for the M17 series mask. The bullet stated that all expired filters must be destroyed by the unit NBC NCO and verified by the command cadre. As it turns out some units were using expired combat filters for training instead of the black ring training filters. The problem was by using expired combat filters, soldiers were being exposed to hazardous metals off gassing from the filters themselves. The bullet also said that any NBC filter over 10 years old should be destroyed. I'm not sure if this applies to the modern 40mm CBRN filters but it's quite possible.

It should go without saying that there are no serviceable filters for the M17 series masks at this point.
 

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Particulate-only Environments

Fortunately, most of the CBRN equation is composed of particulate agents. CS (Tear Gas), radioactive fallout (radioactive vapors and gasses excepted) and biological agents are all classified as particulates. Using a particulate filter (N95, N99, R99, P100, etc) in these environments doesn’t degrade the filter in the manner that a chemical environment degrades a filter. The particulates become trapped on or in the filter medium. Because of this, particulate filters don’t have an established service life. Instead, it is recommended that “All filters should be replaced whenever they are damaged, soiled, or causing noticeably increased breathing resistance (e.g., causing discomfort to the wearer).” How long that takes depends on how much “dust” is in the air. Keep in mind that the filter will become “hazardous” as you use it, so use caution when removing your mask or changing cartridges to prevent self-contamination.
Thank you for the great post. I understand that anything relating to gas/vapor has an "open" shelf life because of chemical reactions. My questions zoom's in on particulate-only environments.

I know you addressed it, but I just wanted to clarify. For every day environments (cutting wood, working in an attic, grinding metal etc)is replacing a filter like a 3m 2091 basically only needed (as far as safety is concerned) when it is so clogged that it's uncomfortable to wear? There isn't risk that it eventually starts letting things through is there? (unless damaged)

What about a Covid type situation? I understand that after use, you shouldn't touch it. But within 24 hours supposedly the virus dies. So can it be worn indefinitely until uncomfortable?

Thanks
 

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Emergency Manager
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Discussion Starter · #7 ·
Thank you for the great post. I understand that anything relating to gas/vapor has an "open" shelf life because of chemical reactions. My questions zoom's in on particulate-only environments.

I know you addressed it, but I just wanted to clarify. For every day environments (cutting wood, working in an attic, grinding metal etc)is replacing a filter like a 3m 2091 basically only needed (as far as safety is concerned) when it is so clogged that it's uncomfortable to wear? There isn't risk that it eventually starts letting things through is there? (unless damaged)

What about a Covid type situation? I understand that after use, you shouldn't touch it. But within 24 hours supposedly the virus dies. So can it be worn indefinitely until uncomfortable?

Thanks

I don’t know that I would wait until it’s “uncomfortable”. When you start noticing resistance, it’s probably a good idea to replace it.

With droplet-borne biologicals, if you get splashed or have large droplets that contaminate the filter you should replace it. As far as I know that’s the only way the contaminants could soak through the filter. Otherwise viral buildup isn’t going to get pulled through the filter media. It’s far more likely to go around before it goes through.

In either case, what you’re trying to avoid is so much dust or particulate buildup that contaminants start bypassing the filter through the face seal or around imperfections in the filter mount or connections.

So yes, as long as it’s not splattered or damaged, and you’re not meeting resistance, you can keep using it.
 

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Any filter used as protection from the COVID19 virus must restrict the flow of all particles with a molecular weight greater than or equal to the virus. When I was using N95s (non-COVID use), we considered them expired in about 4 hours; I do not recall the 3M rating.
 

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Emergency Manager
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Discussion Starter · #9 ·
Any filter used as protection from the COVID19 virus must restrict the flow of all particles with a molecular weight greater than or equal to the virus. When I was using N95s (non-COVID use), we considered them expired in about 4 hours; I do not recall the 3M rating.
Do you mean molecular weight, or diameter? The N95/P100 ratings are based on particulate diameter (>=.3 micron), not mass or molecular weight.
 
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