Quantitative Fit Testing

When the Occupational Safety and Health Administration’s (OSHA) Respiratory Protection Standard, 29 CFR 1910.134, became effective on April 8, 1998, it provided employers with an all-inclusive reference source for fit testing guidelines. Before its revision, the standard made reference to testing a respirator’s “face-piece-to-face seal,” but provided no additional guidance on how to perform the test. The standard now specifies what needs fit testing, the kinds of fit tests allowed, the procedures for conducting them and how frequently fit tests must be performed.

As discussed in Quick Tips #140, Respirator Fit Testing Requirements and Procedures, before an employee is required to use any negative or positive pressure tight-fitting respirator, the employee must complete and pass either a qualitative or quantitative fit test with the same make, model, style and size of respirator that he/she will be using. The fit test must be performed:

• Before initial use;
• Whenever a different style, size, model or make is used;
• At least annually thereafter; and
• If changes in an employee’s physical condition affects the fit
  (dental changes, cosmetic surgery, obvious change in body weight).

OSHA allows for the use of both qualitative and quantitative tests to evaluate a respirator’s fit on an individual. Qualitative fit testing is a pass/fail test to assess respirator fit based on the individual’s response to a test agent. A quantitative fit test assesses respirator fit by numerically measuring leakage into the respirator.

There are advantages and disadvantages to qualitative and quantitative fit testing.

Advantages of qualitative fit testing:

• Low equipment cost
• Simple pass/fail results

Disadvantages of qualitative fit testing:

• Chance of employee deception or bluffing
• Limited protection-factor verification (maximum fit factor of 10)

Advantages of quantitative fit testing:

• No protection-factor limit
• Documentation of numerical results
• No chance of employee deception or bluffing

Disadvantages of quantitative fit testing:

• Expensive up-front equipment costs
• Requires probed face piece or probe adapter
• Annual recalibration of equipment is suggested

Key fit test definitions include:

• Assigned protection factor (APF) means the workplace level of respiratory protection that a respirator or class of respirators is expected to provide to employees when the employer implements a continuing, effective respiratory protection program as specified in 29 Code of Federal Regulations (CFR) 1910.134(c).
• Fit factor means a quantitative estimate of the fit of a particular respirator to a specific individual. It estimates the ratio of the concentration of a substance in ambient air to its concentration inside the respirator.

In accordance with 29 CFR 1910.134(d), when selecting respirators employers must:

• Evaluate workplace hazards and identify user factors and base respirator selection on those factors;
• Provide a sufficient number of respirator models and sizes so that they are acceptable to and correctly fit all users; and
• Use the Table 1 APFs (29 CFR 1910.134(d)(3)(i)(A)) to select respirators that meet or exceed the required level of protection.

OSHA recognizes four types of qualitative fit testing protocol agents: Bitrex® solution aerosol, saccharin solution aerosol, isoamyl acetate (banana oil) and irritant smoke (stannic chloride). For details, see Quick Tips #324: Qualitative Fit Testing.

OSHA recognizes three types of quantitative fit testing protocol agents: generated aerosol, ambient aerosol condensation nuclei count (CNC) and controlled negative pressure (CNP). All three types of quantitative fit testing use a digital instrument that measures airborne particles inside and outside the test respirator or measures vacuum pressure. A special sampling probe takes measurements inside the mask.

1. Generated aerosol uses an aerosol, typically corn oil, that is dispensed in a high concentration into a booth or test chamber and a photometer based aerosol detector that measures the challenge agent that leaks into the face piece. This type of quantitative fit testing is the least used of the three types due to the large size of the unit and the high maintenance involved in cleaning the booth and the components.
2. Ambient aerosol condensation nuclei counting (CNC) instruments, such as TSI brand PortaCount^® equipment, use laser technology to measure aerosol concentrations inside and outside the respirator without the person having to stand in a test chamber or booth. The challenge agent measured consists of ambient microscopic dusts and aerosol particles that are in the air we breathe every day. The particle concentration outside the respirator is measured against the concentration inside the respirator. The ratio of these two numbers is the fit factor.
3. Controlled negative pressure (CNP) systems, such as Occupational Health Dynamics (OHD) Quantifit^® equipment, create a fixed vacuum on the face piece by temporarily cutting off the breathing air with special adapters. The instrument measures the airflow, or leak rate, needed to maintain the vacuum on the mask. The fit factor is then computed by taking an average breathing rate and dividing that number by the measured leak rate. The person being fit tested must remain motionless for the 10 seconds needed to conduct the test. OSHA also requires CNP fit testing to include its REDON protocol. This protocol includes exercises performed facing forward and bending over, shaking the head and two re-donnings of the respirator face piece.

All three OSHA-accepted quantitative fit tests require the face piece being tested to be equipped with high-efficiency particle filters (P100/HEPA) so that no particles enter the respirator and skew the results. TSI PortaCount^® test equipment has an N95 companion, which is used to fit test 95 filter-class respirators. The mask is also equipped with a temporary probe adapter or the person being tested might wear a surrogate mask with a permanent sampling probe. OSHA notes the employer must also ensure that persons administering the quantitative fit tests are able to calibrate the equipment used and perform tests properly, recognize invalid tests, calculate fit factors properly and ensure that test equipment is in proper working order.

Also, all three tests use these eight 60-second exercises:

1. Normal breathing
2. Deep breathing
3. Turning head side to side
4. Lifting head up and down
5. Talking out loud
6. Grimacing (15 seconds)
7. Bending and touching toes (or jogging in place)
8. Normal breathing

For more details on the specific requirements of each of the quantitative test methods, see Appendix A of 29 CFR 1910.134. Because of the equipment requirements for quantitative fit testing, many companies contract with an industrial hygienist or other safety service provider to have the testing performed.

Sources

OSHA’s Respirator Fit Testing Resource Page

TSI Inc.

Occupational Health Dynamics

The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.