Section 84.179 - Silica dust loading test-PAPR series HE filtration(a) Three powered air-purifying particulate respirators will be tested for a period of 4 hours each at a flowrate not less than 115 liters per minute for tight-fitting facepieces, and not less than 170 liters per minute for loose-fitting hoods and helmets.(b) The relative humidity in the test chamber will be 20-80 percent, and the room temperature approximately 25 °C.(c) The test suspension in the chamber will not be less than 50 nor more than 60 mg of flint (99 + percent free silica) per m3 of air.(d) The flint in suspension will be 99 + percent through a 270-mesh sieve.(e) The particle-size distribution of the test suspension will have a geometric mean of 0.4 to 0.6 [MICRO]m and the standard geometric deviation will not exceed 2.(f) The total amount of unretained test suspension in samples taken during testing must not exceed 14.4 mg for a powered air-purifying particulate respirator with tight-fitting facepiece, and 21.3 mg for a powered air-purifying particulate respirator with loose-fitting hood or helmet.