(a) Twenty filters of each non-powered air-purifying particulate respirator model will be tested for filter efficiency against:

(1) A solid sodium chloride particulate aerosol as per this section, if N-series certification is requested by the applicant.

(2) A dioctyl phthalate (DOP) or equivalent liquid particulate aerosol as per this section, if R-series or P-series certification is requested by the applicant.

(b) Filters including holders and gaskets, when separable, will be tested for filter efficiency level, as mounted on a test fixture in the manner as used on the respirator.

(c) Prior to filter efficiency testing of 20 N-series filters, the 20 to be tested will be taken out of their packaging and placed in an environment of 85 ± 5 percent relative humidity at 38 ± 2.5 °C for 25 ±1 hours. Following the pre-conditioning, filters will be sealed in a gas-tight container and tested within 10 hours.

(d) When the filters do not have separable holders and gaskets, the exhalation valves will be blocked so as to ensure that leakage, if present, is not included in the filter efficiency level evaluation.

(e) For non-powered air-purifying particulate respirators with a single filter, filters will be tested at a continuous airflow rate of 85 ± 4 liters per minute. Where filters are to be used in pairs, the test-aerosol airflow rate will be 42.5 ± 2 liters per minute through each filter.

(f) Filter efficiency test aerosols:

(1) When testing N-series filters, a sodium chloride or equivalent solid aerosol at 25 ± 5 °C and relative humidity of 30 ± 10 percent that has been neutralized to the Boltzmann equilibrium state will be used. Each filter will be challenged with a concentration not exceeding 200 mg/m3.

(2) When testing R-series and P-series filters, a neat cold-nebulized dioctyl phthalate (DOP) or equivalent aerosol at 25 ± 5 °C that has been neutralized to the Boltzmann equilibrium state will be used. Each filter will be challenged with a concentration not exceeding 200 mg/m3.

(3) The test will continue until minimum efficiency is achieved or until an aerosol mass of at least 200 ± 5 mg has contacted the filter. For P-series filters, if the filter efficiency is decreasing when the 200 ± 5 mg challenge point is reached, the test will be continued until there is no further decrease in efficiency.

(g) The sodium chloride test aerosol will have a particle size distribution with count median diameter of 0.075 ± 0.020 µm and a standard geometric deviation not exceeding 1.86 at the specified test conditions as determined with a scanning mobility particle sizer or equivalent. The DOP aerosol will have a particle size distribution with count median diameter of 0.185 ± 0.020 µm and a standard geometric deviation not exceeding 1.60 at the specified test conditions as determined with a scanning mobility particle sizer or equivalent.

(h) The efficiency of the filter will be monitored and recorded throughout the test period by a suitable forward-light-scattering photometer or equivalent instrumentation.

(i) The minimum efficiency for each of the 20 filters will be determined and recorded and must be equal to or greater than the filter efficiency criterion listed for each level as follows: