Respirator Fit-Testing for Noobs and Amateurs

I know it’s not a subject that’s of terribly high interest to everyone, but I figured I’d do a couple of paragraphs on properly fitting and fit-testing a respirator. This is not meant for people who are required to use one at work, but aimed at urban explorers, in particular – and anyone else who might have the desire to use respiratory protection in an avocation of their choosing.

The reason for this is simple – there has been a goodly amount of discussion in urban exploration circles on respirator (or gas mask) choice, and while this is a good thing, in that urban explorers are becoming more safety-conscious, nobody seems to be taking a particular interest in how to properly fit the damned things, thereby potentially negating the protection on offer.


There are three kinds of fit-tests done for gas masks and respirators: The first is a basic “fit test”, using positive and negative pressure. This is the easiest to perform – you don the mask or respirator, use your hand(s), or a piece of plastic wrap or something, to obstruct the air inlet(s) and outlet(s), then either breathe in, or breathe out, and hold it for a count of ten. This pressurizes the inside of the mask, and tests the seal with your face. You’ll know within a couple of seconds whether the seal is good or not, as the pressure (or vacuum) will recede.

If these basic tests fail, one (or more) of three things is going on:

1, the mask is the wrong size.
2, the mask is defective.
3, you’re wearing it wrong.

You can try adjusting the mask and repeat the tests, but if you have to work to get it “just right”, you’re probably wearing the wrong size. Respirators are not a one-size-fits-all affair, no matter how much some of the manufacturers like to make you think otherwise.

For a lot of people, this is all the fit testing they’ll ever need to do, and this sort of test is probably perfectly adequate when you’re trying to protect against nuisances – dust, riot-control agents, or unpleasant but not-actually-dangerous odors, for example. If you’re hoping to use a gas mask or respirator to protect against actually dangerous substances, you’ll probably want to perform a more in-depth test.

The best type of test is what’s called a “quantitative fit test”. In it, you wear a specially-adapted mask with a chemical probe inside the mask, are exposed to a known concentration of a control substance for several minutes, and the instruments read what levels made their way past the respirator and filters. For obvious reasons, this isn’t really available to the dilettante.

No, the urban explorer – or other hobbyist – must rely on what’s called a “qualitative fit test”. There are some OSHA-mandated guidelines for this here, but the basic idea is to don a respirator and a chemical/gas cartridge (either an “organic vapor” cartridge, or a full-on NBC filter, if you’re using a gas mask), perform a variety of actions for several minutes while wearing the mask, and then expose yourself to an extremely strong scent for a couple of minutes. If you can detect the odor, you fail. It’s about that simple.

In professional circles, a variety of substances are used for this purpose; the most popular might be banana oil, which is sold for this purpose in little ampules. It is one of the strongest-smelling things I’ve ever run across. You can pick up some from time to time on eBay, or elsewhere online, fairly cheap; do not use this stuff in your house. Seriously. I’d say don’t even use it in your garage – find a vacant, foreclosed house near you, and use their garage, instead. Or use something else – if you have an asian grocery store near you, a jar of shrimp paste will probably work fairly well. If you have a full-face mask or respirator, there are a lot of other things you can try – an OC+CS self defense spray, if you happen to have an outdated can laying around. Failing that, I suspect that chopping up several onions might be a fairly decent ersatz test – if your eyes water even the slightest, your mask probably isn’t working as it should (or your filter(s) only protect against particulates). With half-masks, I suppose you could use perfume, aftershave, body sprays, or similar products that are easy to identify, even at very faint concentrations. (One suggestion I saw a while back was to use animal musk or urine, which are sold as “lures” for hunters. Great, I guess, if you’re a hunter, and have some laying around, but the stuff’s expensive, and harder to find than shrimp paste… plus I suspect that some of the urines may have enough ammonia to make your eyes water, if you use a half-mask.)

Whatever you use, if, after a couple minutes’ exposure, you still can’t detect the odor, your mask or respirator fits properly, yay. If you can detect the substance, then either your mask doesn’t fit so great after all, or your filter or cartridge doesn’t protect against whatever it is you’re using, suggesting it’s only a particulate filter. (Or is now only a particulate filter – the protection offered by other types of filters degrades with age, so most if not all of those old “NATO” gas mask filters being sold so cheap as “NBC filters” now are only effective against particulates, and sometimes questionable even for that application.)

Like I said before, this isn’t a substitute for proper “official” tests, administered by trained professionals certified in your city or country. But for non-professionals, it’s – purely in my opinion, mind – better than nothing, and more than adequate for your typical urban explorer, who will encounter nothing more hazardous than asbestos particles…

Published in: Geekiness, General, Urban Exploration | on March 3rd, 2010| Comments Off on Respirator Fit-Testing for Noobs and Amateurs

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