N95 Respirators, or any other dust mask style respirators with a NIOSH designation, are required to be fit tested. OSHA calls these respirators tight-fitting, filtering facepieces. They used to be called dust masks.
They define "filtering facepiece" as "a negative pressure particulate respirator with a filter as an integral part of the facepiece or with the entire facepiece composed of the filtering medium.1"
A negative pressure respirator is one in which, during inhalation, the air pressure inside the mask is negative compared to the ambient air pressure outside the mask.
We can think of it this way: with such respirators, inhalation creates negative pressure inside the respirator. This negative pressure is what helps "pull" the outside ambient air towards and through the mask. This means that any contaminants contained in the outside or ambient air are also "pulled" towards the mask. The filtration media of the mask is then supposed to trap the contaminant.
The problem here is that if the mask is not fitted properly, some amount of contaminant will not be filtered out. Why?
When an inhalation occurs, the air and the contaminants it contains, will follow the path of least resistance into the negative pressure created inside the respirator. If there are any gaps (even if not visible to the naked eye), some of the contaminated air will be sucked into the nose and/or mouth. They will not be filtered out by the N95. This is why these respirators need to be fit tested.
It is important to note that any tight-fitting negative air respirator (like an N95) cannot be fit tested on an individual with facial hair. All individuals must be clean shaven. Facial hair compromises the seal and creates an entry point for contaminants.
OSHA specifically says that tight-fitting facepieces (like N95s) are not to be worn by those who have, "facial hair that comes between the sealing surface of the facepiece and the face or that interferes with valve function.2"
Caution - Filtration Rating Considerations
A word of caution is needed. Even a properly fitted respirator will not keep out contaminants if that respirator's filtration media is ineffective against the contaminant in question. An N95 respirator is ineffective at filtering out, for example, lead particles, asbestos particles, or welding fumes. This is true even if properly fitted.
These contaminants are too small for the N95 filtration media. Asbestos, for example, is less than a micron and can be as small as .02 microns.3 An N95 simply cannot filter these particles out. Many of them will pass right though the filtration media and/or a compromised seal.
It is hard to think this can happen when looking at an N95 with the naked eye. It looks impenetrable. It is not. (It is worth noting that the SARS-CoV-2 virus is .07-.09 microns--also smaller than 1 micron.4)
So before the fit test process even begins, one must make sure that the filtration media of the N95 respirator can actually filter out the contaminate in question. NIOSH does provide assistance. It can be found here.
Fit Testing Methods
There are two categories of fit tests--qualitative and quantitative. OSHA defines each of these.
A qualitative fit test "means a pass/fail fit test to assess the adequacy of respirator fit that relies on the individual's response to the test agent." The most common test of this type is either a sweet (saccharin) or bitter (bitrex) solution dispensed through a nebulizer, or irritant smoke tubes. Irritant smoke tubes, however, cannot be used to fit test an N95 respirator. Like asbestos, the irritant aerosol it produces is too small to be filtered out by an N95 respirator.
A quantitative fit test "means an assessment of the adequacy of respirator fit by numerically measuring the amount of leakage into the respirator." The most common type of quantitative fit test involves the use of a PortaCount machine. This is an expensive machine usually only found in labs that do workplace medical evaluations.
The most common type of fit test for an N95 respirator is the qualitative fit test. Specifically, the sweet or bitter solutions dispensed through a nebulizer. We sell the Allegro qualitative saccharin fit test.
At the end of this article, you will find instructional/how-to information.
Effectiveness of Fit Testing
Fit testing works. It does enable one to find the best-fitting N95 for his or her face. You will always end up with better protection having gone through a successful fit test.
However, N95's are difficult to fit test no matter the method used. Some methods are better than others.
NIOSH studied the effectiveness of the various fit test methods with N95 respirators. They came to the following conclusions:
This chart lists the fit test method on the left. "QNFT" stands for a quantitative fit test. "QLFT" stands for a qualitative fit test. The chart lists the Simulated Workplace Protection Factor (SWPF) on the bottom.
What is the Simulated Workplace Protection Factor? An SWPF of 10, for example, means that the air inside the respirator is 10 times cleaner than the air outside the respirator--20 is 20 times cleaner, etc. An SWPF of 1 means the air inside the respirator is the same as the air outside.5
This chart shows that fit testing an N95 respirator using a quantitative fit test is far better than the qualitative methods. Passing a fit test on a PortaCount machine in an N95 respirator means the N95 is filtering out more contaminants (20.5 SWPF) than passing a fit test with a qualitative method of fit testing (7.9 to 11 SWPF).
However, a successful fit test of an N95 respirator using a qualitative method results in better (7.9 to 11 SWPF) contaminant protection than no fit test (3.3 SWPF). A surgical mask, which for a variety of reasons cannot be fit tested, provides virtually no contaminate protection at all (1.2 SWPF).
Importantly, OSHA requires that multiple make and models of N95s be available for the employee to try out. This is because all faces aren't the same. Someone may fail a fit test on a 3M 8210, for example, but pass using a Moldex 2200N95.
Finally, it is not uncommon that a worker may fail a fit test even though several different masks have been tried. In such a scenario, a half mask cartridge type respirator may be required.
Respirator Fit Test Instructions
You can download a 3M PDF containing their qualitative fit test instructions here. Below is an instructional video from Allegro on a qualitative fit test using saccharin or bitrex: