The Fit Test Process

Exactly What You Need

The TSI Portacount is an ambient particle counting device which is used to conduct Fit Testing by providing a quantitative assessment of face-seal leakage.

A fit factor is a measure of how well a particular face piece seals against a person’s face. It is expressed as a ratio of the concentration of challenge aerosol outside a respirator to the concentration of aerosol that leaks into the respirator through the face seal. A fit factor of 100 means the air inside the mask is 100 times cleaner than the air outside. The measurements made during face fit tests are an assessment of respirator fit at the time of testing only. Respirator fit at all other times will vary. The Fit Factor value is not intended for use in calculating an individual’s actual exposure to hazardous substances

The Portacount works by measuring the concentration of microscopic dust particles in the ambient air and then measuring the concentration of those dust particles that leak into the respirator. The ratio of these two concentrations is called the fit factor.

The person being tested will be asked to don the selected respirator ensuring it is correctly fitted in accordance with the manufacturer instructions.  A mirror will help the wearer don and adjust the mask correctly.  The wearer should perform a fit check to ensure the face-piece has been correctly fitted. 

The wearer will be asked to perform test exercises (see below) during the test to generate a physical workload that simulate working activities and work rate. This will test the fit of the facepiece better than if the wearer was at rest.

Once the face fit test process is completed the Portacount test device will produce a Fit Test Report with the numerical values attained at each stage of the test and an overall fit factor.  Should the fit test process fail to attain the minimum fit factor level for the specific respirator at any of the test stages the test will be aborted and a failed test report produced.  The tester should examine the potential reason for the failed test with a view to retest the wearer once any adjustments have been made or with an alternative size, make or model if required.

Fit test exercises for quantitative ambient particle counting:

  • Normal breathingThe wearer should breathe normally with no head movements or talking.

  • (ii) Deep breathing. The wearer should breathe slowly and deeply, taking care not to hyperventilate.

  • Turning head side to sideThe wearer should slowly turn their head from side to side between the extreme positions on each side (approximately 15–20 times per minute). The head should be held at each extreme momentarily so the wearer can inhale at each side.

  • (Moving head up and downThe wearer should slowly move their head up and down (approximately 15–20 times per minute). The wearer should inhale in the up position (ie when looking toward the ceiling).

  • TalkingThe wearer should talk slowly and loudly enough to be heard clearly by the fit tester. The wearer should read from a standard reading passage (Rainbow passage) or count down from 100.

  • Bending over from a normal standing position, the wearer should bend at the waist as if to touch their toes and then return to an upright position. Repeat approximately 10–15 times throughout the duration of the exercise.

  • Normal breathing, same as first exercise


HSE - Guidance on Using Disposable Respirators