Quantitative Fit Testing

Quantitative Fit Testing is the most accurate form of respirator fit testing, a data-driven approach to determining the fit of a respirator on an individual’s face. Proper fit testing saves lives. Many types of masks can be tested including N-95 Filtering Face Pieces, Half-Face Masks, and Full-Face Respirators.

On the other hand, Qualitative Fit Testing is reliant on the wearer’s senses of taste or smell to determine whether or not the respirator’s seal is sufficient. This is a much less reliable method of testing, as it is subjective, the ability to sense or taste the challenge agents varies widely among test subjects, and can be cheated by dishonesty from the person being tested.

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Who Needs Quantitative Fit Testing?

Quantitative fit testing is common in many industries that deal with potential hazardous chemicals or inhalants. A few examples are healthcare, environmental, manufacturing, and so many more. For an example, check out this video to understand the importance of quantitative fit testing for firefighters:

Quantitative vs Qualitative

There are multiple ways to break down the differences between Qualitative fit testing and Quantitative fit testing. Quantitative is data-based, provides a real objective metric, and usually tests the actual mask individuals will wear to protect them. Qualitative is based on a  series of sensory questions.

Quantitative Qualitative
Accurate and produces a defensible metric Not Accurate – completely subjective
Positive Result Can’t Be Cheated by Test Subject Test Subject can report inaccurate response
Faster, Less than 3 minutes OSHA-compliant Fit Test takes about 23 minutes
Does not require hood and toxic challenge agent Claustrophobic, requires use of potentially carcinogenic challenge agents
Verification Check provides defensible proof of instrument performance Results Aren’t Verified – No defensible verification

Fit Testing In-Depth: Quantitative vs Qualitative

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.

Key Terms

  • Respirator Fit Test: A test that checks whether or not a respirator properly fits and seals against the face of the user.
  • Qualitative Fit Test: A method of testing that utilizes the wearer’s reactions to substances to test the fit of a respirator mask.
  • Quantitative Fit Test: A method of testing that utilizes specialized equipment to measurably test the amount of leakage around the seal.
  • Isoamyl Acetate: A banana-smelling substance used to test elastomeric masks.
  • Saccharin: An aerosol perceived as sweet that’s used to test elastomeric and filtering respirators.
  • Denatonium: A substance that is mixed with water and sprayed to detect gaps in fit. It has a bitter taste.
  • Irritant Smoke: A smoke that causes irritation and discomfort.

FAQ

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 assess?

In reality Qualitative Fit Testing assesses only the test subjects’ ability to sense the challenge agent and his or her truthfulness.

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.

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