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Understanding respirator fit testing

31 October 2022

IF YOU or your colleagues use any kind of tight fitting respiratory protection equipment then you should already know that you should be conducting fit testing regularly to ensure the fit of the mask to the face of the wearer is good enough to provide adequate protection.

First of all its important to understand respirators leak; they can never provide 100% effective protection but they do provide some protection; the question is how much? In order to provide any protection, there has to be some kind of barrier, or seal, between the face of the wearer and the air that contains the hazard that the wearer is trying to avoid; given that this barier is formed on the face of the wearer and that every person has a uniquely shaped face it is no real surprise that there is a risk of leakage at this point and that if this leakage is too big, then the respirator will simply not provide the level of protection required.

QNT and QLT are the two types of test available that measure this leakage; QLT tests assess the QUALITY of the seal using an agent that is detectable by the wearer of the mask, the assumption being that if the wearer does not detect the agent, then the mask must not be leaking. It sounds simple and it is but there is are some big BUTs! What if the wearer is not sure if they can detect the agent or not, what if there is no agent to detect? If conducted properly then this test method can be effective but it is also only suitable for testing masks that are likely to be used in low risk environments as this test method is just not senistive enought to measure small leaks that could be fatal in high risk ones.

QNT testing QUANTIFIES the leakage by accurately measuring the volume of test agent outside the mask and then also measuring how much is inside the mask; two key points here already, the wearer is no longer the device that measures or detects the test agent so there is no subjectivity and also there has to be test agent outside the mask (in sufficient quantity) otherwise the mask is not being challenged. This type of test can be used to test ALL types of mask that are used in ALL risk environments. Not only that but as the wearer is not being subject to any smell or taste, if a respirator is found to leak then a re-test can be conduct immediately so downtimes are reduced significantly.

There are two technologies used for QNT testing, the difference being the test agent that is detected: CNP (Controlled nagative pressure) detects pressure change to measure leakge and APC (Ambient Particle Counting) uses naturally occuring microscopic particles. Both are extremely sensitive at detecting leakage into the mask and both have limitations but APC is the only one that can be used to test all mask types, including Full, Half and disposable FFP (N95) types which surprisingly are the type that really should be tested most as they are the type of mask that is most likely to leak!

Fire Safe International says that AccuFIT 9000 delivers APC QNT fit test with confidence.