Fit Testing with the TSI Portacount

This page gives answers to our most frequently asked Portacount-related questions.

To download TSI’s Quick Start guide to the Portacount 8040 & 8048 Click Here

What is a Portacount?

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

What is Quantitative Fit Testing?

There are two different types of Fit Testing: Qualitative and Quantitative. The TSI Portacount is a Quantitative Fit Testing device  which produces direct numerical results called a Fit Factor.

What is Respirator Fit Testing?

Respirator Fit Testing is a method for determining if a person knows how to wear a particular respirator and if that respirator matches the person’s facial features adequately.

Which type of respirators require Fit Testing?

Fit Testing is required for all respirators with tight-fitting facepieces i.e. those where the performance of the respirator depends on a tight seal between the mask and the user’s face, This includes positive pressure masks, full face, half face and filtering facepiece (disposable) masks.

What is a Fit Factor?

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.

What Fit Factor Pass level should I use?

The following Fit Factor Pass Levels should be used when conducting fit testing with the TSI Portacount:
FFP1: n/a
FFP2: 25*
FFP3: 100
Half Face Mask:100
Full Face Mask: 2000
*if used in conjunction with the N95 a pass level of 100 should be used.

How does the Portacount work?

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 HEPA filter cartridges stop essentially all the particles so anything that gets into the mask must have come through the face seal.

What particle size range can the Portacount measure?

The 50% cut-off for small particles is 0.02 micrometers (µm). This means that half of the 0.02 µm particles are counted and half are not. As soon as the particle size reaches about 0.04 µm, almost 100% are counted up until a particle size of about 1.0µm. Few particles larger than 1.0 µm are counted by the instrument because they impact and stick inside the switching valve or some other component. Statistically speaking, there are very few particles above 0.1 µm in normal ambient air. The percentage of particles counted is called “counting efficiency”. Counting efficiency is also a function of how much alcohol is in the Portacount.

What ambient levels are required when using the TSI Portacount?

The Portacount requires a minimum ambient level of 1000 particles/cm3 for normal operation however current UK guidance (INDG 479) recommends the following minimum ambient particle concentration:

Half & Disposable Masks: 3,000 particles/cm3

Full Face Masks: 10,000 particle/cm3

What if I don’t have enough ambient particles?

Ambient particle concentration can be raised in a number of ways, the recommended procedure is to use the TSI Particle Generator (Model 8026) which generates a reliable source of particles in the correct size range for the Portacount to measure. Alternative methods include the use of tea-light type candles.

How is the Portacount affected by fluctuations in ambient particle levels?

The Portacount takes an ambient particle measurement before and after each mask sample. The average of the two concentrations is used to calculate the fit factor. This eliminates problems with normal ambient fluctuations. Fit Test Operators using the Portacount should check the ambient particle count using count mode to make sure that there are no wild fluctuations. If fluctuations vary more than 20 percent in 60 seconds, then they should move to a more suitable location.

How often should the Zero Check and Max. Fit Factor Check be performed on the Portacount?

You should always do a Zero Check and Maximum Fit Factor Check when you first start fit testing each day. Both checks can be completed in less than 2 minutes.

Does the Portacount work with powered air purifying respirators (PAPR's)?

Yes. However, just as with SCBAs, fit testing must be done with the mask in negative-pressure mode. This is most often accomplished by using an identical face piece in a negative-pressure version with HEPA filters. Most respirator manufacturers offer negative-pressure versions of the same face piece used for their PAPRs.

Does the Portacount work with self-contained breathing apparatus (SCBA) such as used by fire fighters?

Yes. However, to really test the fit of the face piece, the respirator must be tested in negative-pressure mode using HEPA filters. This is most often accomplished by using an identical face piece in a negative-pressure version with HEPA filters. Most respirator manufacturers offer negative-pressure versions of the same face piece used for their SCBAs

How long does an alcohol wick last in the PORTACOUNT

The life of an alcohol wick varies depending on the ambient conditions where you do your fit testing. Accumulation of moisture is the most common problem and occurs most often in areas of high humidity. If the Service message comes on and adding alcohol does not cause it to go off, changing the wick is often required. Wicks that have been completely dried out can be reused. If the wick looks worn or is severely discoloured it should not be reused. Three uses from one wick is typical

We always clean the test mask for each fit test to avoid spreading germs from person to person, but what about the moisture that collects in the Portacount sample tube. Can someone be exposed to moisture from a previous test subject?

TSI has tested the Portacount and determined that the air flowing through the tubes cannot reverse direction.


What is a suitable substitute for the Rainbow Passage if the test subject cannot read or doesn't speak English?

The reason for the talking exercise is to test the fit of the respirator while the person’s mouth and jaw are moving. If the Rainbow Passage cannot be used, ask the candidate to count backwards from 100 down to 1.

When a person fails the fit test, how do I know if the problem is the way the mask is worn, the size of the mask, a bad filter, or a defective mask?

The reason for a poor fit factor can be difficult to determine. The experience of the test operator will often determine whether or how quickly the problem is resolved. Performing a Zero Check and Maximum Fit Factor Check as described in the Portacount Operation & Service Manual will tell you if the problem is with the Portacount or the mask. If you are using a shared test respirator that has a history of fitting well, you know that the problem is either donning technique or improper size. If you test employees in their own respirator using a fit test adapter, you could also have a defective mask. Trial and error is often the only recourse.

Where can I buy fit test adapters?

Fit Test Adapters connect to the inhalation (or sometimes exhalation) port of the facepiece and allow a sample tube to pass through into the inner masks in order that a sample of air can be drawn from the breathing zone of the wearer. Fit Test Adapters are available for all makes and models of masks – see our extensive list of adapters here.

Why should a person refrain from smoking for 60 minutes before being fit tested with the Portacount?

It has been shown that smokers exhale particles for about 60 minutes after smoking. The Portacount counts these particles as particles that have leaked into the mask. The result is that the person being tested will get a lower Fit Factor than they should have.

Do I have to remove the alcohol cartridge from my Portacount before I ship or store it? What happens if I forget?

You should always remove the cartridge and replace it with the storage cap whenever you ship or store the Portacount. If you do not, you risk flooding the instrument. The storage cap keeps dirt out of the Portacount. A little dirt in the wrong place can cripple the instrument. Discipline yourself to always use the storage cap.

How often should the Portacount be re-calibrated?

If the only aerosol you use it with is ambient air, your Portacount will not need cleaning more than once a year. The unit should zero using the supplied HEPA filter and pass the maximum fit factor test. The Portacount should be calibrated annually – please contact us to arrange calibration including our collect and return courier service.

Training Dates


Fri 16th April 2021: FULL
Fri 14th May 2021: spaces
Fri 18th June 2021: spaces

Fri 23rd April 2021: FULL
Thur 20th May 2021: spaces
Fri 25th June 2021: spaces


We're sorry, there are no courses available at this venue currently due to Covid-19 restrictions.


We're sorry, there are no courses available at this venue currently due to Covid-19 restrictions.


We're sorry, there are no courses available at this venue currently due to Covid-19 restrictions.


We are happy to arrange on-site training courses for 3 or more delegates anywhere in the UK. Please contact us for details.