::: TL;DR

• Make sure to fit test. It is not a user seal check.
• If you think you've failed a fit test, you've failed.
• For everyday use, it's almost never the filter; replace the exhalation valve. :::

Users of elastomeric respirators are usually concerned about their filters. I mean, you change your filters in your furnace every year (or if you're paranoid, every season). Maybe you don't need to change it as often as an N95, but shouldn't you have to change your elastomeric filters, say every six months?

Well, I'm going to cover in later post why throwing out old, unused filters is, surprisingly, almost never necessary (but only if you aren't stressing it by grinding stone or removing asbestos... or anything else that requires a respirator), but in short:

It's almost never the filter.

But you know what does need changing every six months? That's just as exposed to dust as the filters? A piece of rubber that, if you fail to pay attention, can plummet your fit factor scores to single-digit surgical mask territory?

Notes When Fit Testing Your Respirator

Besides the commonly given advice to:

• Fit test, with the help of Bitrex/Saccharin + a nebulizer, or, if you're healthy, irritant smoke,

• fit test at regular intervals (which is usually how faulty exhalation valves and changing faces are discovered),

• and do user seal checks (located in your respirators manual, usually),

The most important thing to remember is never ignore failures.

• If you coughed, even slightly in, say, an irritant smoke test, you've failed the fit test and need to investigate what went wrong.

I had previously swapped an exhalation valve with one from another respirator, promptly forgot about it, and inadvertently swapped it back, assuming the irritant smoke test was faulty. It wasn't. After that, only regular testing with a CPC caught the failure.

If you do happen to only have a CPC, here's a telltale sign of exhalation valve failure:

• Do repeated exercises of Normal Breathing-Deep Breathing.

• Normally, after the first exercise, you'll notice a slight drop in fit factor when 'Deep Breathing' compared to 'Normal Breathing.' This is because there's an increase in filter penetration when 'Deep Breathing.'

• But, if the exhalation valve is leaking, you'll notice a 'Normal Breathing' score lower than a 'Deep Breathing' score, well into the third exercise and beyond.

• You'll usually notice this pattern on multiple attempts.

If your respirator isn't visibly damaged, replace the exhalation valve immediately. Alternatively, if you feel a stream of air leaking, your respirator does not fit and needs to be replaced with a different brand or size.

And of course, unless the exhalation valve is absolutely destroyed, you won't be able to detect this mode of failure on current CNP fit testing machines. Makes you wonder why OSHA is still allowing this style of fit test...