Levitt-Safety Blog

Respirator fit testing tips and tricks: Basic troubleshooting

Jonathan McCallumMarket Segment Manager: Occupational Health, Industrial Hygiene & Environmental MonitoringApril 17, 2018

If you’ve ever performed QNFT (quantitative) respirator fit testing, you know that the process can sometimes be challenging and interspersed with occasionally failed results which require you to retest.

The reason we perform respirator fit testing is to verify that the user can obtain an effective seal and level of comfort with their chosen respirator.  We also want to make sure that the respiratory protection being worn provides the user with the best possible protection when required.  The fit test is an opportunity for the user to demonstrate their level of competence with donning, doffing, and user seal check training.  CSA Z94.4 requires that we repeat the test every other year or when there is a change to the respirator, physical condition of the user, or PPE being worn.

Here are some tips, tricks, and basic troubleshooting suggestions that we have learned over the years to help with your QNFT fit testing program.

Filtering Facepiece (N95) Seal

So many masks to choose from, so many faces to fit. There is no such thing as one size fits all. A common reason that N95 respirators don’t fit (besides being too big or too small) is that the metal nose piece isn’t properly fitted. Once a respirator is chosen, proper donning procedures will instruct users to use two hands (two fingers on each hand) to form the metal band evenly over their nose.  Using one hand (thumb and index finger) can create an uneven bend resulting in a respirator leak.

A 3M disposable respirator with valve.

Filtering Facepiece (N95) Probe Placement

A fit testing probe needs to be installed in order to conduct a fit test on a filtering facepiece respirator.  Respirator leaks can be created when installing this probe.  It is important that the probe be installed to the left or right of exhalation valves and away from seams in respirator material.  Start by inserting the probe to the midway point on the inside of the facepiece.  Then, continue while applying pressure on the sealing push nut/rivet.  When done correctly, respirator material should be seen around the joint of the 2 components.


First off, CSA Z94.4 stipulates that no facial hair may come into contact with the seal area of the respirator.  Annex M in the Standard provides guidance on what is acceptable. Basically, if facial hair is – or could be – in the mask sealing area, you can’t conduct a fit test.

Maintenance & Hygiene

Everyone is aware of the potential transmission of germs and bacteria via our hands. If you’re fit testing, here are some useful tips to for the safety of the fit tester and respirator user.

  • Wear disposable non-latex gloves when handling someone else’s respirator
  • If a shared “test”  respirator needs to be wiped out between uses, have the person being tested do the wiping. If they bring their own respirator for the test, offer a wipe so it can be cleaned.  This promotes respirator hygiene and provides a clean respirator for the test.
  • Always verify that all components of the respirator are in place prior to the fit test.
  • When putting a mask adapter on a respirator, use new, clean tubing to go from the mask adapter to inside the mask. The fit test adapter kits come with replacement tubing and additional can be ordered as needed.
  • Occasionally, moisture can condense in the twin tubes between the respirator fit tester and the mask adapter. This occurs because exhaled breath is humid and can condense in the hose during testing. The easy solution is to carry a spare, ‘clean’ twin-tube that you can swap out on demand.  They can also be cleaned and dried as necessary.

Low Particle Counts

Most of the time, the new generation of fit testers have a very low minimum particle count threshold for N95/P100 or elastomeric mask testing. Sometimes, though, when testing indoors, there are not enough particles present to get a statistically valid sample. This usually occurs when the ventilation system works so well that the air coming into the room has really been cleaned of most of its particulate load.

If we need to generate particles, they have to be non-toxic and easy to develop, so we use a  particle generator and salt water. The result is a generated mist that evaporates off the water, leaving a very small salt particle in the air. The respirator fit tester device counts these particles and we can continue our testing.

Proper Particle Generator Usage

Like everything else in life, there’s a right way and a wrong way to use a particle generator:

  • Keep the generator and the fit test instrument at least 5 feet apart.
  • Note the air currents in your room and make sure the air is flowing towards, not away from, your test subject or client
  • Your room should be small and minimally ventilated to allow particulate concentrations to build up quickly
  • You don’t need a lot of salt for this to work properly. A small tablet in a container of water is enough.
  • For devices that use a CNC detection engine, low particle counts can also occasionally occur because the alcohol in the wick is running low, the alcohol has been contaminated (high ambient RH),or low quality alcohol has been used.  If unsure of alcohol quality, replace prior to  testing.


CSA says the test subject needs to wear the PPE they normally wear on the job when receiving a fit test, and it makes sense. If you wear a hard hat, safety glasses and hearing protection, they should not interfere with your mask. When you really need your mask, it is a bad time to find out that your safety glasses don’t fit with your respirator.


Smokers inhale a lot of particulate, but it can take at least 30 minutes for all those small particulates to migrate out of the lungs. If you test too soon after smoking, the instrument will count those particles and won’t be able to tell if it’s a leak or cigarette smoke that is resulting in particles showing up in the test.

Equipment Failure

Sometimes the equipment doesn’t work. Not often, but not never. Remember, it’s drawing air in when it’s turned on, so never let the hose fall to the floor without a filter on it. Dust bunnies are bad for the optics. So is bouncing and bumping – sometimes this causes an optics misalignment to occur, so the instrument stops counting particles.


Quantitative respirator fit testers require annual calibration.  Please verify the calibration date on your fit tester prior to testing.

This isn’t an exhaustive list by any means, but it covers off the many of issues that users seem to experience most frequently.

Ready to book your fit test appointment with us? Get started today.