Quantitative Fit Testing Guide

Quantitative Fit Testing

Quantitative Fit Testing can be defined as using fit testing equipment to measure the leakage around the face seal of a respirator facepiece to calculate a “fit factor”. A fit factor is essentially the ratio of the concentration of a challenge agent in the ambient air divided by the concentration of the challenge agent in the breathing zone. A Fit Factor of 100 is required for half-face respirators and a minimum fit factor of 500 for a full-face respirator (29CFR 1910.134). 

There are Three Methods for Quantitative Fit Testing Approved by OSHA:

Ambient Aerosol

This method uses as a challenge agent the naturally-occurring ultrafine particulates in the ambient atmosphere. (Advances in HVAC technology have in many instances reduced the ambient concentration of these particulates to a level which requires the generation of extra particulates in order to have a sufficient concentration for testing.) The concentration of the ultrafine particulates is sampled in the respirator via a sample adapter which enables the instrument to collect a breathing zone sample while the test subject performs a series of movements which are designed to stress the seal. This concentration is compared to the ambient particulate concentration. The instrument uses a technique known as Condensation Nuclei Counting (CNC) to size-enhance and count the particulates.

Controlled Negative Pressure

As an alternative to aerosol fit test methods, this method creates a slight negative pressuring inside the temporarily sealed respirator face piece and then maintains a constant negative pressure for several seconds. The measurement of the exhaust stream that is required to hold the pressure in the temporarily sealed respirator constant yields a direct measure of leakage air flow into the respirator. The major disadvantage of the CNP method is that it does not allow the test to be performed in a dynamic manner, i.e., the test subject must remain completely still while the leakdown is measured. Thus, the respirator fit is not checked while the test subject is moving and breathing as would occur in normal workplace activities.

Generated Aerosol

Using a high concentration of an aerosol introduced into a booth or test chamber, a photometer-based aerosol detector measures the challenge agent that leaks into the face piece. This was the original method developed at Los Alamos, but with the development of the CNC instruments and the extensive infrastructure required to support this method, it is becoming extremely rare.

Qualitative Fit Testing

This can best be defined as a pass/fail test measuring a subject’s ability to detect any leakage of gas into the respirator based on taste, smell or reaction to an irritant by the user. Using OHSA’s approved methods of testing, the user should be able to do the following without reaction; breathing normally, breathing deeply, turning head from side to side, moving head up and down as well as talking. This testing applies to half-mask respirators such as N95 face masks.Due to the fact that qualitative fit tests cannot be considered equivalent to quantitative methods, and because full-face respirators require a true minimum fit factor of 500, the qualitative methods cannot be used for full-face respirators.

Types of  Qualitative Testing Methods Set By OSHA:

Isoamyl Acetate Screening

Odor threshold screening, performed without wearing a respirator, is intended to determine if the individual tested can detect the odor of isoamyl acetate at low levels (banana smell).

Saccharin Solution Aerosol Screening

Taste threshold screening, performed without wearing  a respirator, is intended to determine whether the individual being tested can detect the taste of saccharin (sweet tasting).

Bitrex (Denatonium benzoate) Screening

Taste threshold screening, performed without wearing a respirator,  is intended to determine whether the individual being tested can detect the taste of Bitrex (bitter taste). 

Irritant Smoke (Stannic Chloride)

Test uses a person’s response to the irritating chemicals release in the “smoke” produced by a stannic chloride ventilation smoke tube to detect leakage into the respirator of the irritant smoke.

What is a Quantitative Fit Test?

A Quantitative Fit Test can best be defined as one which does not depend on the ability of the test subject to detect a challenge agent, nor does it depend on the truthfulness of reporting the sensing of the challenge agents and is therefore completely objective. Further, a Quantitative Fit Test provides defensible metrics and automatically captures results into a secure database for future reference.

What is Fit Testing Required For?

29 CFR 1910.134 describes in detail why fit testing must be performed and who must be tested. Briefly, any worker who is exposed to a respiratory insult and who is required to wear a respiratory protective device (respirator) must be fit-tested prior to wearing the respirator in performance of his or her duties.

What does Qualitative Fit Testing Assesss?

How Often Should Fit Testing Be Done?

29 CFR 1910.134 requires that fit testing be performed annually. Please refer to our post on annual fit testing.

Is Fit Testing Mandatory?

29 CFR 1910.134 describes in detail the requirements for who must be fit tested.

How Long is Fit Testing Valid?

One Year

Is Fit Testing a Legal Requirement?

29 CFR 1910.134 states that a written, formal Respiratory Protection Program (RPP) be established in any organization where respiratory protection is required. Although the requirements for training of personnel administering the fit tests are somewhat vague, the implication is that the Administrator of the RPP is responsible for the criteria for training the person who actually conducts the fit tests. Please refer to this Cornell University piece.