Skip Content



Quantitative Fit Testing

Quick Tips #318

An employee required to use a negative or positive pressure tight-fitting respirator must undergo a fit test with the same make, model, style and size of respirator, according to OSHA regulations. The fit test must be performed:

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

A fit test uses qualitative or quantitative protocol to evaluate a respirator's fit on an individual. Qualitative fit testing (QLFT) is a pass/fail test to assess respirator fit based on the individual’s response to a test agent. A quantitative fit test (QNFT) assesses respirator fit by numerically measuring leakage into the respirator.

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

Advantages of qualitative fit testing:

  • Low equipment cost of about $50 to $150
  • Simple pass/fail results

Disadvantages of qualitative:

  • Chance of employee deception or bluffing
  • Limited protection-factor verification

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; approximately $5,000 to $10,000
  • Requires probed face piece or probe adapter
  • Annual recalibration of equipment is suggested

Key fit-test definitions include:

  • Assigned Protection Factor (APF) is the level of respiratory protection that a respirator or class of respirators is expected to provide when an effective respiratory program is implemented.
  • Fit factor is a quantitative estimate of the fit of a respirator to a specific individual. It typically estimates the ratio of the contaminant concentration in air to the concentration inside the respirator.

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

  • Evaluate workplace hazards, 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 Assigned Protection Factors (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: 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: Generated aerosol, ambient aerosol 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 the TSI brand Portacount, 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, and the ratio of those two numbers is the fit factor. This system typically tests a P100 (HEPA) filter. However, the TSI Portacount has an N95 companion, which is used to fit test 95 filter-class respirators, such as N95 disposable filtering face-piece respirators.
  3. Controlled negative pressure (CNP) systems, such as the Occupational Health Dynamics (OHD) Fit Tester 3000, creates 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 redonnings 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. 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.

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

Not only does OSHA require fit testing, but it is a crucial step in the verification of respirator selection and proper respirator usage. Quantitative fit testing is commonly used in applications were higher fit factors are required. Quantitative fit testing equipment is also expensive, so many companies will contract with an industrial hygienist or other professional, or possibly rent the instrument and perform the test themselves.


TSI Inc.
Occupational Health Dynamics

(Rev. 1/2012)

Find even more information you can use to help make informed decisions about the regulatory issues you face in your workplace every day. View all Quick Tips Technical Resources at

Think Safety. Think Grainger.®
Grainger has the products, services and resources to help keep employees safe and healthy while operating safer facilities. You’ll also find a network of safety resources that help you stay in compliance and protect employees from hazardous situations. Count on Grainger for lockout tagout, fall protection equipment, confined space products, safety signs, personal protective equipment (PPE), emergency response and so much more!

Please Note:
The content in this newsletter is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific compliance questions should refer to the cited regulation or consult with an attorney.

©2015 W.W. Grainger, Inc.