What Happens During a Fit Test?

Procedure and Measurements

A fit test helps to ensure that a respirator fits correctly to a wearer's face, providing the necessary protection against airborne particles. The term "fit" in this context refers to how well the mask conforms to the wearer’s face, providing a tight seal. 

Understanding the Fit Test

The primary purpose of a fit test is to verify that a respirator, such as an N95, FFP2 or FFP3 respirator, seals tightly against the wearer's face. This seal prevents potential pathogens from penetrating the mask through tiny leaks. The tight fit is crucial for the mask to function effectively, filtering out hazardous particles from the air.


Measurement

A quantitative respirator fit tester such as the TSI PortaCount™ Respirator Fit Tester evaluates the seal of a respirator by connecting the device to the respirator or mask while the employee is wearing it. This device counts microscopic particles in the ambient air, which are invisible to the naked eye but present in the air we breathe. A tube attached to the respirator allows the instrument to measure the air inside the mask. If the respirator fits correctly, very few particles will be detected inside because the respirator’s filter prevents these particles from passing through. However, if the respirator fits poorly, gaps between the respirator and the face allow environmental particles to enter, increasing the particle concentration inside the respirator.

 

Performance During the Measurement

To simulate real-world conditions, the fit test with a quantitative fit tester includes a series of prescribed movements, based on the fit test protocol utilized. These exercises are designed to mimic everyday activities that might affect the fit of the respirator. The PortaCount™ fit tester's software guides the test subject through these movements with animations, ensuring the correct sequence and execution. The exercises are not physically demanding and include actions such as:

  • Normal breathing
  • Deep breathing
  • Moving the head up and down
  • Moving the head side to side
  • Talking
  • Bending over

These movements help determine if the respirator maintains its seal during typical workplace activities.

 

Understanding the Fit Factor

The fit factor is a key measurement in the fit test. It is the ratio of the particle concentration in the ambient air (COut) to the concentration inside the mask (CIn). The formula for the fit factor is:

Fit Factor= COut / CIn​

After each exercise, the fit factor is calculated. The overall fit factor is then averaged over all the exercises. Different types of masks or respirators have specific minimum fit factor thresholds that must be met. For FFP masks for instance, the minimum fit factor required to pass the fit test is 100. A fit factor of 100 means the respirator is performing effectively, providing the intended level of protection.

Procedure and Measurements During a Fit Test

  1. Preparation: The employee selects an appropriate respirator and undergoes a medical evaluation to ensure they can safely wear a mask.
  2. Initial Seal Check: A user seal check is performed to ensure the mask is donned correctly before the test.
  3. Connecting a quantitative fit tester such as the PortaCount™ Respirator Fit Tester: The fit tester is attached to the respirator, and baseline measurements of particle concentrations are taken.
  4. Performing Exercises: The employee performs a series of movements while the PortaCount™ Respirator Fit Tester measures particle concentrations inside and outside the mask.
  5. Calculating the Fit Factor: The fit factor for each exercise is calculated, and an overall fit factor is determined.
  6. Evaluation: The results are evaluated to determine if the respirator provides an adequate fit. If the fit factor meets or exceeds the required threshold, the respirator passes the test.

Post-Test Procedures

After the fit test, the results are documented, including the type of respirator, size, and fit factor achieved. The employee receives training on how to properly don and doff the respirator, as well as how to maintain and care for it. Regular fit testing is recommended to ensure ongoing protection, especially if there are changes in the wearer's facial structure or if a different respirator model is used.


Importance of Regular Fit Testing

Fit testing is not a one-time procedure. It should be conducted regularly to account for changes in the wearer's face or mask design. Consistent testing ensures that the respirator continues to provide effective protection against airborne hazards.

Learn More About Respirator Fit Testing

 

Related Resources

Respirator Fit Test Protocol Comparison

Learn about the main similarities and differences of the US OSHA protocol, the British Fit2Fit protocol (HSE INDG 479 and the corresponding Fit2Fit companion) and the ISO 16975-3 protocol.

Read More

Respirator Fit Testing Explained

Learn the essentials of respirator fit testing for workplace safety! Our video covers qualitative and quantitative tests, proper procedures, and best practices to protect workers from respiratory hazards.

Read More