42 CFR §84.175

1. (a)Three filters from each powered air-purifying particulate respirator for efficiency will be tested against a neat cold-nebulized dioctyl phthalate (DOP) or equivalent aerosol at 25 ± 5 °C that has been neutralized to the Boltzmann equilibrium state.
2. (b)Single air-purifying particulate respirator filter units will be tested in an atmosphere concentration of 100 mg/m 3 of DOP at the following continuous flow rates for a period of 5 to 10 seconds:
3. (c)Powered air-purifying particulate respirators with multiple filter units will be tested by dividing the flow rate specified in paragraph (b) of this section by the total number of filters used.
4. (d)The filter will be mounted on a connector in the same manner as used on the respirator and the total efficiency must be ≥99.97 percent.