Qualitative Vs Quantitative Face Fit Testing...
Qualitative Versus Quantitative Face Fit Testing.
In this article, we look at the pros and cons of Qualitative (the taste test – AKA QLFT) Versus Quantitative (Ambient Particle Counting (APC) AKA QNFT) Face Fit Testing.
Firstly, they are both recognised Respiratory Protective Equipment (RPE) Face Fit Test methods as prescribed by HSE Guidance document INDG479. This document actually details the three recognised fit test methods, Controlled Negative Pressure (CNP) being the other however it is not suitable for FFPs (disposable masks) so we won’t detail that in this particular blog.
For the record, Face Fit Testing is a legal requirement under UK H&S legislation and must be undertaken by a competent person; 1974 Rapport Ltd is Fit2Fit approved to test AND train in both methods.
The basic theory, really basic! (further reading available on our website)…
Qualitative (QLFT) aka “The Taste Test”– The RPE wearer is positioned inside a hood whilst wearing the RPE. The hood is filled with a challenge aerosol, they are required to undertake a series of seven exercises each lasting 60 seconds. If the wearer doesn’t taste the aerosol, then the mask appears to fit (seal) and protect. If they do taste the test aerosol, then the mask does not fit and protect.
Quantitative (QNFT) aka (Ambient Particle Counting) – The RPE is first prepared to allow a particle count to be taken within the RPE using laser diffraction, the particle count within the mask is then compared to that in the surrounding atmosphere thus yielding a numerical value known as a fit factor. Again, a series of seven exercises are performed, each lasting 85 seconds (25 seconds of purging, 60 seconds of measurement).
Qualitative testing – The bad bits!
This test method relies heavily on the competence of the tester; the difference between an average test and a robust test can be negligible. There really is a skill to this test method and a poor test process result in people wearing RPE that doesn’t offer the required level of protection.
This method relies on taste; some people are unable to recognise the taste of the test aerosol meaning the test simply does not work for some individuals.
Correct nebulizer use is essential, they can easily underperform, be use incorrectly or be somewhat unpredictable and inconsistent. Continual checking is required.
There can be possible viral transmission risks from testing multiple individuals using the same hood; this can be counteracted by cleaning and sanitization, but this also makes the process more time consuming.
Any remaining solution left in the nebulizer must be disposed of (as per current HSE guidance) and the nebulizer immersed in a sterilant of the required strength for the appropriate amount of time; again, this makes the test method waster full and time consuming.
QLFT is only appropriate to half face RPE (reusable or disposable) offering particulate protection. It CANNOT be utilized on full face RPE.
The test outcome can be manipulated by the wearer, they can intentionally give false pass or false failed results (hard to believe but I’ve encountered it many times!).
It is subjective, not definitive, there can be confusion over the result and invalid or inconclusive outcomes can be achieved.
It is a time-consuming process when done correctly, especially in the event of failed results or testing on multiple devices.
Ultimately transportable and no power source required.
The result is either a "Pass or Fail", it is not quantifiable.
Qualitative testing – The good bits!
It’s cheap! Circa £150 should get you a face fit test kit.
Its relatively easy to train people how to conduct a test (a comprehensive one-day cousre is sufficient for most learners) meaning that many organisations are able to bring this method “in house”.
It is a HSE recognised test method.
The wearer gets an immediate, physical indication if the mask does or does not fit and protect. This can and will encourage RPE use and give confidence in the device; or oppositely, deter them form wearing ill-fitting RPE.
Quantitative testing – The bad bits!
Its expensive, wildly expensive. A basic set up is circa £10k and so many employers would elect to call in a competent, extremal tester (such as 1974 Rapport!) to undertake this testing for them.
It is destructive to FFPs and 28 day “maintenance free” masks.
The skill for this method relies on preparing the RPE, preparing the wearer, controlling the atmosphere, and navigating the test software.
The test exercise protocol cannot be broken down into stages, the full test must be completed in “one hit” as it were, if needed, QLFT could be broken down.
For reusable respirators, you must purchase adapters, each device needs a unique adapter; these can range from a few pounds to several hundred pounds, again making it expensive.
The test equipment needs annual calibration and servicing, you guessed it, expensive!
Consumable and sundry items such as N95 probes, compressed air, isopropyl alcohol, salt tablets… add another expense.
The tester must carefully manage and control the surrounding ambient particle levels, QNFT is not suitable for all working environments.
The tester will need to investigate and verify suspiciously high fit factors, a skill often gained through experience.
Similarly, consideration must be given to wearer generated particles within the respirator.
A power source is required.
The equipment can be bulky and is very sensitive; consideration must be given to carefully transport it.
Daily checks are required, it can be time consuming to set up for just a couple of tests.
The wearer gets no real / physical indication if the mask protects or not, it’s purely a numbers game!
Quantitative Testing – The good bits!
Its accurate, deadly accurate, an amazing fit test method!
It can be used to test on both full or half face RPE (must have a degree of particle filtration (P2 or P3).
It tests down to a smaller particle size range than QLFT.
There is no reliance on taste.
The RPE wearer is largely unable to falsify results, its definitive when conducted correctly.
It automatically generates a test report.
It gives a quantifiable, numerical outcome known as a fit factor, the higher the fit factor the more protection is offered. The HSE set minimum fit factors to be achieved for both full and half face RPE.
You can run a live reading before undertaking the full test protocol, a good use of time and an opportunity to explain the test theory to the wearer.
A skilled tester can begin to work out why a mask may have failed and try to remedy accordingly.
Although the test exercise protocol is slightly longer than QLFT, it is actually a much much faster test method overall (no need to allow residual aerosol tastes to clear), especially when testing multiple devices and or in the event of a failed result.
It can be used to show wearers how incorrect donning or poorly maintained RPE can compromise performance.
The above points are in no way intended to be exhaustive and are based on many years of first-hand experience as a fit2fit approved trainer and tester having completed thousands of tests and trained hundreds of individuals; this is my opinion!
When testing, I predominantly opt for QNFT, it just works for me in so many ways however it is a huge financial investment for most employers unless there is a heavy reliance on RPE and many individuals requiring regular testing.
In my humble, both test methods have their place. I’ve heard many calls for QLFT to be rescinded but for me it remains a valid option. If we were only ever to rely on QNFT then I fear, we would see even fewer workers receiving a face fit test and being left exposed to airborne hazards.
Face fit testing isn’t just a legal obligation, it’s a moral obligation!
In closing, when seeking testing OR training, please ensure that you select a competent person. Competent testers and trainers can be found on the fit2fit website. Here you will also find a host of resources including the three fit2fit companions giving detailed practical advice on the face fit testing methodology.
Take care out there folks!