Respirators: What Do I Need For the Job?
In a previous article we looked at the difference between quantitative and qualitative fit testing for respirators. We saw that quantitative fit testing is far more effective, and the TSI Portacount series are the best quantitative testing device.
But how can this help to determine which type of mask should be worn for a job? For that you need to know a few numbers, and first among them is the Fit Factor.
Fit Factors and Respirators
With qualitative testing the Fit Factor is either 0 (fail) or 100 (pass). Because the Portacount is a much more sensitive piece of equipment the Fit Factor can be more specific, and much higher than 100.
The Portacount works by measuring the amount of a particulate both outside and inside the respirator. Any particulate found inside the mask must have have seeped in from outside. The ratio of particulate outside the mask to the amount inside the mask is the fit factor.
Assigned Protection Factor
Along with the Fit Factor there is also the Assigned Protection Factor (APF). The APF is a number OSHA assigns to each mask. For example, an N95 mask has an APF of 10. A full face mask would have an APF of 50.
To consider it an appropriate fit the Fit Factor must be at least ten times the APF. In cases where this number is higher than 100 it is necessary to carry out a quantitative test.
The PEL and the MUC
Finally, two other numbers that factor in to finding the appropriate respirators is the Permissible Exposure Limits (PEL), which the relevant regulatory body assigns to the chemical, and the Maximum Use Concentration (MUC), or the maximum amount of a substance a worker can use.
The MUC is calculated by multiplying the PEL and the APF together. For example if you are working with Acetone, which has an OSHA assigned PEL of 1000, and were using an N95 mask, with an APF of 10, the MUC would be 10,000, which is 24,000mg/m3.
When dealing with a more noxious chemical, for example Bromine, which has a PEL of 0.1, according to OSHA, using an N95 would only allow the use of 7 mg/m3 of the substance. To use more would require a heavier mask.
Depending on your jurisdiction, Exposure Limits should be published and available through the local Occupational Health and Safety organization.