Four Steps to Quantitative Fit Testing

If you use a negative or positive pressure tight-fitting respirator on the job, OSHA regulations say you need to be fit tested with the same make, model, style, and size of respirator you’ll use in your daily operations.

To stay in full OSHA compliance, these tests are supposed to be run before the first time you use the respirator on the job; whenever you change mask style, size, or model; if your physical condition changes that would affect mask fit (dental changes, facial cosmetic surgery, addition or removal of eyeglasses, or obvious changes in body weight). Then, you should be tested every year after that.

First, there are a few things you should know about respirator fit and the fit testing procedure.

Let’s start with the basics.

My mask has an assigned protection factor. Is it the same as a fit factor?

An assigned protection factor and a fit factor are not the same.

An Assigned Protection Factor is the level of respiratory protection, as determined by the respirator manufacturer, that a respirator is expected to provide under standard working conditions. This is an overall standard for the respirator itself, and has nothing to do with the employee.

A Fit Factor is a quantitative estimate of how well the respirator fits the intended wearer. A fit factor is the calculated ratio of contaminant concentration in the air to contaminant concentration inside the respirator. Different types of respirators have expected fit factors: OSHA requires that people wearing full face respirators must be able to minimally achieve a Fit Factor of 500 or better. For half face masks, the fit factor must be 100 or more.

One of the most frequently used types of quantitative fit testing is ambient aerosol nuclei count (CNC).

How does a CNC fit test work?

PortaCountPro8038Ambient Aerosol Nuclei Count (CNC), as implemented by TSI’s PortaCount family uses 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.

What’s involved in the test?

Not only does OSHA require fit testing, but it’s crucial in verifying the proper respirator selection and making sure each wearer understands how to use it.

First, you’ll put on your mask and check for comfort and adequate fit.

  • Does the mask sit properly across the bridge of your nose and against your cheeks?
  • Is there room for eye protection or glasses (if needed)?
  • Do you have room to talk?
  • Is there adequate tension in the strap or is it too tight? Does the respirator slip out of position?
  • Is the respirator the proper size to span the distance from your nose to your chin?

Then, you’ll wear the mask for up to five minutes prior to the exercise test.

The exercise test includes several one-minute activities, and a 15-second grimace (where you break the seal between the mask and your face, and then let it return to normal fit).

  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

So, which respirator fit test system should I use?

It depends entirely on the type of respirator you’re testing. The TSI PortaCount Pro 8030 is OSHA and NFPA accepted for tight-fitting respirators. If you’re familiar with the older PortaCount Plus system, it’s the upgrade to the TSI 8020.

Only the TSI PortaCount Pro+ 8038 is approved for testing N95 disposable masks (plus P1 and P2). So, if you’re testing N95 masks for hospital use, the TSI 8038 is the model you need. The 8038 replaces the old PortaCount Plus 8028 N-95 testing system.

TSI’s PortaCount Pro family eliminates the guesswork associated with tedious and error-prone qualitative fit test methods. PortaCount Pro and Pro+ quantitative fit testers measure fit while the user performs a series of moving, breathing, and talking exercises that are designed to simulate the same movements users make in the field.

The PortaCount has a color touchscreen with graphical interface, so you don’t need a PC to fit test; It stores results in a database for permanent record and easy test retrieval. However, the unit has no internal memory, so data is stored on a flash drive. Data from the flash drive is easily transferred to a PC for storage.

Have a need for speed? With upgrades to TSI’s PortaCount firmware, you’re now able to link multiple PortaCount units together, and test up to four people simultaneously.

Though other quantitative methods may do a portion of the fit test faster, in the long run, the PortaCount’s OSHA-approved CNC fit test method provides several additional benefits. (Read the TSI Whitepaper here.)

The team at RAECO is ready and willing to support you in selecting the model that best meets your fit testing needs. Plus, we offer free video training on TSI PortaCount products through our online Training Center.

Want to learn more?

Read more posts on Respirator Fit Testing

See the TSI PortaCount Pro at

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