A fit test is carried out on an N95 mask

Fit Testing Basics - Qualitative or Quantitative?

The recent COVID-19 outbreak has brought the subject of masks back into public conversation. If you believe the news all you need to do is grab an N95 mask to protect your face. The truth is you need to put the mask through fit testing first.

It is important that the fit of each person’s mask provides greatest protection. Although an ill-fitted mask is better than no mask, and any mask is better than none.

Those working in high-risk environments should always make sure to fit their mask as well as possible. This is true whether on the front lines of a viral pandemic, or a chemist working with noxious gases. Do this through Fit Testing.

There are two types of Fit Testing, qualitative, and quantitative.

Qualitative Tests

Qualitative fit testing is the older form. It is less accurate, and is only works with certain respirators and masks.

There are four qualitative tests. All of them rely on the test subject wearing the mask and telling tester if they can identify the chemical by either smell or taste. If they can identify the chemical then the mask does not have a proper fit, otherwise it does.

The four chemicals used are Isoamyl Acetate (banana oil), Saccharin, Bitrex aerosol, and Irritant smoke. The last test is both more dangerous and less reliable than the other three. However the various OHS organizations across Canada and the US allow it with conditions.

Quantitative Fit Testing

Quantitative testing is a far newer development, pioneered by TSI in the ‘80s. It is far more accurate than qualitative testing and is the only testing method for many types of masks, including any type of full face mask.

Using a device such as a TSI Portacount 8040 or Portacount 8048 a mask can be tested to fit two ways. First it can be tested over time to demonstrate how well it fits through normal usage. Second it can be tested in real time to ensure the mask fits properly.

The Portacount works by measuring the amount of microscopic dust particles in the ambient air, and then measuring the concentrations of those same dust particles inside the mask. The Fit Factor is the ratio between those two concentrations.

While a Fit Factor of 100 is a successful quantitative test, qualitative tests can go much higher. The quality of the seal, coupled with the mask type will determine how high the Fit Factor can go.

The Fit Factor required to work with certain substances may vary with the type of mask used. As an example in the United States OSHA gives each mask type an Assigned Protection Factor (APF). This number determines the minimum Fit Factor of a mask, as well as the amount of a exposure to dangerous dangerous substances a worker can have.

Ideally it would be better if we could all avoid any exposure to dangerous contaminants or viruses, but that is not always possible. By making sure the masks we wear fit properly we can progress toward keeping ourselves, our colleagues, and those we love safe.

27 août 2020
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