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What is a mask seal check? And are they reliable?

Credit: 3M


You may have heard of doing 'seal checks' (aka fit checks) on respirators such as N95s, P2s, and reusable elastomeric masks.


A user seal check (not to be confused with a fit test) is performed to determine if the respirator has been donned (put on) properly and check for overt air leakage around the facepiece.


The user seal check can be a positive pressure or negative pressure check - or both.


But are seal checks reliable? Can they accurately predict if a mask is fitting properly? And can they be a substitute for fit testing?


In this article, we'll answer these questions and show you how to do negative and positive pressure seal checks on disposable and reusable respirators.


Seal Checks On Disposable N95/P2 Respirators


Positive Pressure Seal Checks


To perform a positive pressure seal check on most styles of disposable masks, both hands are placed over the respirator and the user exhales sharply.


The mask should balloon out a bit and no air should be felt escaping the mask.


If air leaks are felt coming out around the edges of the mask - and the mask doesn't fill up with air - this means the respirator has 'failed' the positive pressure seal check.


For duckbill style masks, most manufacturers' instructions do not require the user to cover the facepiece with their hands. Simply exhale to check for leaks and ensure the facepiece balloons out.


If the disposable respirator has an exhalation valve, positive pressure seal checks are not appropriate. Perform a negative pressure seal check instead (see below).


Negative Pressure Seal Checks


To perform a negative pressure seal check, cover the front of the respirator with both hands and inhale sharply. The mask's facepiece should collapse indicating there are no overt air leaks. The wearer shouldn't feel any air leaking around the edges of the mask.


These are general techniques for performing seal checks on most N95/P2 masks. Always refer to manufacturers' instructions to ensure you're conducting the seal check correctly.



Seal Checks on Reusable Respirators



Credit: Oregon OSHA



Positive Pressure Seal Checks


To conduct a positive pressure seal check on a reusable respirator, cover the exhalation valve and then exhale into the facepiece. See the left side of the drawing above.


The seal check is considered appropriate if a positive pressure is built up inside the facepiece without any evidence of outward leakage of air around the seal.


For some respirators, you may have to remove the exhalation valve cover before covering the valve.


Negative Pressure Seal Checks


To conduct a negative pressure seal check on a reusable respirator, cover the filters or cartridges with both hands and inhale sharply. The facepiece should collapse inward and no air leakage should be detected. See the right side of the drawing above.


These are general techniques for performing seal checks on most reusable respirators. Always refer to manufacturers' instructions to ensure you're conducting the seal check correctly.


Are Seal Checks a Reliable Way to Check the Fit?


First, it's important to note that seal checks are never a substitute for fit testing.

Fit testing is a requirement for all tight-fitting respirators under the AS/NZS 1715:2009.


In fact, the CDC recommends that seal checks only be performed when a respirator has passed a fit test.


Studies have shown that seal checks are not reliable and their predictive value is pretty dismal, especially for disposable respirators.


After conducting thousands of fit tests, we agree - seal checks don't accurately predict if the person will pass or fail a quantitative fit test.


In our experience, a lot of people can't tell if the air is leaking out or not when they perform the positive or negative pressure seal check. We've seen people say they definitely can't feel any leaks and then go on to fail a quantitative fit test. Or they say they can feel an air leak, but go on to pass a quantitative fit test with flying colours.


We've witnessed masks doing what they're supposed to do during positive and negative pressure seal checks (filling up with air or collapsing down respectively) and they still fail the fit test.


That said, we always teach people how to do seal checks in line with all international fit testing standards, including the AS/NZS 1715:2009.


And we remind folks that seal checks should never take the place of a fit test.



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