(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 m 3 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 µm 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.