Fit testing and user seal checks · HSE-240 Lesson 9

A tight-fitting respirator protects only as well as it seals. Faces vary enormously in size and shape, and no single model fits everyone. Fit testing is how a program confirms that a specific make, model and size of respirator seals on a specific worker's face. User seal checks are the quick daily checks that the respirator is on correctly. This lesson explains both, along with the facial hair rules that cause so much friction in workplaces.

Why fit testing matters

Studies of workers wearing respirators without fit testing have repeatedly found that many achieve only a fraction of the expected protection, and some get almost none. A half mask with an APF of 10 that leaks badly may deliver a real protection factor of 2 or 3. Fit testing does two things. It screens out respirators that do not seal on a particular face, so the worker can be offered a different model or size. And it trains the worker in how a good fit feels, which improves how they put on the respirator every day.

When fit testing is required

Fit testing is required for every tight-fitting respirator, including filtering facepieces, elastomeric masks and tight-fitting PAPRs and supplied-air respirators. CSA Z94.4 calls for fit testing before first use, at least every two years, and whenever a change could affect fit. British Columbia requires fit testing at least once a year (OHS Regulation s. 8.40), and Ontario's Regulation 833 requires fit testing by qualitative or quantitative methods as part of the written measures and procedures. Check your jurisdiction and your own program, which may set a shorter interval.

Triggers for fit testing.
Trigger	Examples
Before first use	New worker; new respirator program
Change of respirator	Different make, model, style or size
Periodic	At least every two years under CSA Z94.4; annually in BC and in many employers' programs
Change in the face	Significant weight change, dental work, facial surgery or scarring
Worker reports poor fit	Leakage, discomfort, difficulty sealing

Fit testing applies only to tight-fitting facepieces. Loose-fitting hoods, helmets and visors do not need it. Fit testing must also be done with the same model and size the worker will use at work, and while wearing any other equipment that could affect fit, such as safety glasses, hearing protection or a hard hat.

Qualitative fit testing

A qualitative fit test (QLFT) is a pass or fail test that relies on the worker detecting a test agent by taste, smell or irritation. The worker first takes a sensitivity test without a respirator to confirm they can detect the agent. Then, wearing the respirator inside a hood or enclosure, they perform a series of exercises while the agent is introduced. If they detect the agent, the test fails.

Qualitative fit test agents.
Test agent	Detected by	Notes
Isoamyl acetate (banana oil)	Smell	Requires organic vapour cartridges
Saccharin	Sweet taste	Works with particulate filters; widely used for filtering facepieces
Denatonium benzoate (Bitrex)	Bitter taste	Works with particulate filters; harder to ignore than saccharin
Irritant smoke	Involuntary cough	Uses an irritant aerosol; requires care; less commonly used now

Qualitative tests are simple and inexpensive but limited. Because the result depends on the worker's honest response and senses, they can only confirm a fit factor of about 100. They are therefore permitted only for respirators that need a fit factor of 100 or less, which in practice means half masks and filtering facepieces, and full facepieces only when they are used in atmospheres where a half mask would be sufficient.

Quantitative fit testing

A quantitative fit test (QNFT) measures how much leaks in. The most common method uses a condensation particle counter, such as a PortaCount, that counts tiny ambient particles outside and inside the facepiece through a probe or adapter. The ratio is the fit factor. Other methods generate a test aerosol, or use controlled negative pressure (CNP) to measure the leak rate when the facepiece is briefly sealed and air is drawn out.

\[FF = \frac{C_{\text{outside}}}{C_{\text{inside}}}\]

Each exercise in the test produces its own fit factor. The overall fit factor is not the simple average but the harmonic mean, which gives more weight to the exercises where the fit was worst. This reflects how leakage actually adds up: a few seconds of poor fit let in far more contaminant than many minutes of good fit keep out.

\[FF_{\text{overall}} = \frac{n}{\frac{1}{FF_1} + \frac{1}{FF_2} + \cdots + \frac{1}{FF_n}}\]

The standard protocol uses exercises that simulate work movements: normal breathing, deep breathing, turning the head side to side, moving the head up and down, talking aloud, bending over and normal breathing again. A grimace exercise may be included to break and reset the seal but is not counted. Shorter protocols for certain respirator types have been validated and are accepted in both countries' practice.

CSA Z94.4 sets pass criteria for quantitative tests based on the facepiece type, generally a fit factor of at least 100 for half facepieces and at least 500 for full facepieces, consistent with US practice. Check the edition your regulation references.

A bar chart of fit factors for seven fit test exercises on a logarithmic scale: normal breathing 850, deep breathing 620, head side to side 410, head up and down 95, talking 280, bending over 330 and normal breathing 900. A dashed line marks the overall harmonic mean of about 300 and a second line marks the pass level of 100 for a half mask. — Exercise fit factors and the harmonic mean. One poor exercise pulls the overall fit factor far below the simple average.

Worked problem

Calculating an overall fit factor

A worker's quantitative fit test on a half-mask respirator gives these exercise fit factors: 850, 620, 410, 95, 280, 330 and 900. Calculate the overall fit factor and decide whether the test passes.

Show solution

Reciprocals: 1/850 = 0.00118; 1/620 = 0.00161; 1/410 = 0.00244; 1/95 = 0.01053; 1/280 = 0.00357; 1/330 = 0.00303; 1/900 = 0.00111.
Sum = 0.02347.
Overall fit factor = 7 ÷ 0.02347 = 298.
The simple average would be 498, but the harmonic mean is 298 because of the poor head up and down exercise.
298 is at least 100, so the half mask passes.

Answer: The overall fit factor is about 298, which passes for a half mask. The low result during head movement up and down suggests reviewing strap tension and nose fit with the worker.

Worked problem

When one exercise causes a failure

On a full-facepiece test, a worker's exercise fit factors are 4,000, 3,500, 2,800, 3,000, 120, 2,500 and 4,200. The talking exercise was 120. Does the respirator pass, and what should the fit tester do?

Show solution

Reciprocals: 0.00025, 0.00029, 0.00036, 0.00033, 0.00833, 0.00040, 0.00024. Sum = 0.01020.
Overall fit factor = 7 ÷ 0.01020 = 686.
The pass level for a full facepiece is 500, so the test passes, but the talking exercise shows a seal weakness.
The fit tester should check strap adjustment and facepiece size, and discuss with the worker whether a different size would seal better during speech.

Answer: It passes with an overall fit factor of about 686, but the weak talking result is a warning sign worth addressing, especially if the job involves a lot of talking.

Conducting a good fit test

A fit test is also a training session. A good fit tester checks medical clearance first, confirms the worker has not eaten, smoked or chewed gum shortly before a taste test, offers several models and sizes, lets the worker choose the most comfortable respirator that seals, observes donning, and explains what was seen. CSA Z94.4-18 added a comfort assessment as part of fit testing, recognizing that a respirator that hurts after an hour will not be worn properly for a shift.

Common fit test failures and responses.
Common reason for failure	Response
Wrong size	Try another size of the same model
Face shape does not suit the model	Try a different model or manufacturer
Straps too loose, twisted or placed wrongly	Retrain on donning and repeat
Stubble or facial hair	Shave and retest, or use a loose-fitting respirator
Eyewear temple bars or hearing protection break the seal	Use spectacle kits in full facepieces or compatible equipment
Worker cannot tolerate the respirator	Refer for medical review; consider a PAPR

User seal checks

A user seal check is a quick test the wearer does every time a tight-fitting respirator is put on, to make sure it is seated properly. It is not a substitute for a fit test, but it catches twisted straps, displaced facepieces and damaged valves.

User seal checks.
Check	How to do it	What a good seal looks like
Positive pressure check	Cover the exhalation valve and exhale gently	The facepiece bulges slightly with no air escaping around the edges
Negative pressure check	Cover the inlets of the cartridges or filters and inhale gently, holding for about 10 seconds	The facepiece collapses slightly and stays collapsed, with no air leaking in
Filtering facepiece check	Cup both hands over the respirator and exhale sharply (and inhale for unvalved models), following the manufacturer's instructions	No air felt leaking at the nose or edges

If a seal check fails, adjust the respirator and repeat. If it still fails, do not enter the contaminated area; report it so the respirator can be inspected or the worker refitted.

Facial hair and other interferences

Facial hair that lies under the sealing surface of a tight-fitting respirator breaks the seal. Research shows that even a day or two of stubble measurably reduces fit factors, and beards can reduce protection dramatically. That is why both countries require tight-fitting respirator users to be clean-shaven where the respirator seals. Moustaches and other facial hair that stay entirely inside the facepiece without touching the seal or interfering with valves may be acceptable.

Two cross-sections of a respirator edge against skin. On the left, the clean-shaven face shows the sealing flange in full contact with skin. On the right, stubble and beard hairs hold the flange away from the skin, creating channels through which contaminated air leaks inward during inhalation. — Facial hair under the seal creates leak channels. Allowed facial hair must stay completely inside the facepiece.

CSA Z94.4 requires that nothing interfere with the facepiece seal, including facial hair, and the 2018 edition added guidance on facial hair, eyewear and dentures. Where a worker's facial hair is a matter of religious observance, Canadian human rights law requires the employer to accommodate up to the point of undue hardship. The usual accommodation is a respirator that does not depend on a face seal, such as a loose-fitting PAPR or supplied-air hood, where it provides adequate protection.

Other interferences include spectacle temple bars passing under a full-facepiece seal, which is why full facepieces need special spectacle inserts; head coverings or hoods under the straps; jewellery; and dentures, whose removal can change face shape. Workers who wear corrective lenses, hearing protection or hard hats with respirators should be fit-tested wearing them.

Worked problem

Planning for a clean-shaven policy

A plant introduces a clean-shaven requirement for 40 workers who wear half masks. Twelve workers have beards, two of them for religious reasons. How should the program respond?

Show solution

Explain the reason for the requirement with evidence about seal leakage, not just a rule.
Give workers who choose to shave a reasonable period and fit test them once clean-shaven.
For the two religious accommodation requests, assess whether loose-fitting PAPRs provide adequate protection for their tasks; they usually do for exposures within an APF of 25.
Consider offering PAPRs to other bearded workers too, if the cost is reasonable and the protection adequate.

Answer: Combine clear explanation, fit testing and loose-fitting alternatives. The religious accommodation is legally required unless it causes undue hardship, and PAPRs are typically a reasonable solution.

Common mistakes

MistakeIssuing one size of respirator to everyone without fit testing.
InsteadFit test each worker on the exact make, model and size they will use, and offer alternatives.
MistakeAveraging exercise fit factors arithmetically.
InsteadUse the harmonic mean, which reflects how leakage adds up.
MistakeUsing a qualitative fit test for a full facepiece needed at more than 10 times the limit.
InsteadQualitative tests confirm only a fit factor of about 100; use a quantitative test where more is needed.
MistakeTreating a passing seal check as a fit test.
InsteadSeal checks confirm donning each time; fit tests confirm the respirator suits the face.
MistakeAllowing a day or two of stubble under a tight-fitting seal.
InsteadRequire clean-shaven sealing surfaces, or provide a loose-fitting respirator.
MistakeFit testing without the safety glasses and earmuffs worn at work.
InsteadFit test with all equipment that could affect the seal.

Summary and key terms

Fit testing confirms that a specific respirator seals on a specific face and trains workers in good fit.
Fit testing is required before first use, at least every two years under CSA Z94.4, annually in BC, and after changes.
Qualitative tests use taste, smell or irritation and can confirm a fit factor of about 100 only.
Quantitative tests measure leakage; the overall fit factor is the harmonic mean of exercise fit factors.
Pass levels are generally 100 for half facepieces and 500 for full facepieces.
User seal checks are done every time a tight-fitting respirator is put on and do not replace fit testing.
Facial hair under the seal is not permitted; religious accommodation is usually provided with loose-fitting respirators.

Fit test: A test that confirms a tight-fitting respirator seals on a particular wearer.
Qualitative fit test (QLFT): A pass or fail fit test based on the wearer detecting a test agent.
Quantitative fit test (QNFT): A fit test that measures leakage numerically.
Fit factor: The ratio of the concentration outside the respirator to that inside during a fit test.
Harmonic mean: The number of values divided by the sum of their reciprocals; used to combine exercise fit factors.
Condensation particle counter: An instrument that counts very small particles to measure fit factors.
Controlled negative pressure (CNP): A quantitative fit test method that measures leak rate under a set negative pressure.
User seal check: A positive or negative pressure check done by the wearer each time a respirator is put on.
Clean-shaven: Free of facial hair where the respirator seals against the skin.
Undue hardship: The legal limit of an employer's duty to accommodate.

Practice problems

Work each problem on paper first, then reveal the answer to check.

Name two things fit testing achieves.
Show answer
It screens out respirators that do not seal and trains workers in what a good fit feels like.
How often does CSA Z94.4 call for fit testing?
Show answer
Before first use, at least every two years and after changes; BC requires annual testing.
Why are qualitative tests limited to respirators needing a fit factor of 100 or less?
Show answer
They rely on the wearer's senses and can only confirm a fit factor of about 100.
Calculate the overall fit factor for exercise fit factors of 200, 200, 50 and 200.
Show answer
4 ÷ (0.005 + 0.005 + 0.02 + 0.005) = 4 ÷ 0.035 = 114.
Why is the harmonic mean used rather than the average?
Show answer
It reflects how leakage adds up, giving more weight to poor-fit exercises.
What are the usual pass levels for half and full facepieces?
Show answer
100 for half facepieces and 500 for full facepieces.
Describe a negative pressure seal check.
Show answer
Cover the inlets, inhale gently and hold; the facepiece should collapse slightly and stay collapsed.
Why are spectacle inserts used in full facepieces?
Show answer
Temple bars passing under the seal would cause leakage.
What is the usual accommodation for a worker with a religious beard?
Show answer
A loose-fitting PAPR or supplied-air hood that does not rely on a face seal, where it gives adequate protection.
A worker fails a fit test with a medium half mask. Name two next steps.
Show answer
Try another size or model, check strap placement and donning, check for facial hair or eyewear interference.