How the Portacount works

The TSI Portacount is the most widely used and trusted Quantitative Fit Test method. The Portacount provides a direct assessment of respirator fit by comparing the concentration of ambient dust particles outside the facepiece to the concentration of particles that have leaked into the facepiece. The ratio of these two concentrations is called the Fit Factor:

TSI Portacount Equation

Since the microscopic particles in the air are not able to pass through the HEPA filter used on the face mask, any particles which are detected inside the facepiece are assumed to have come from a faceseal leakage.

The Portacount is based on a miniature continuous flow Condensation Nucleus Counter (CNC). This type of device takes particles that are too small to be easily detected and grows them, using condensation of alcohol vapour, to a size where they are large enough to be detected.

The Portacount uses a bespoke computer programme which runs an automated fit testing procedure. The software controls the test sample timing, test exercises and pass levels and allows the operator to input candidate / mask specific information. Data in the form of Fit Test Records can be printed as individual reports showing all results achieved or selected on the basis of a number of parameters including test date or location.


Read the Portacount Theory of Operation application note on the TSI website here


Training Dates


Friday 21st June
Friday 19th July
Friday 16th August
Friday 20th September

Friday 5th July
Friday 9th August
Friday 6th September


Thursday 20th June
Thursday 18th July
Thursday 16th August


Wednesday 7th August
Thursday 29th September


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