Measurements of the efficiency of respirator filters and filtering facepieces against radon daughter aerosols.

The filtration efficiencies of respirator filters and filtering facepieces have been tested against radon daughters in a fluorspar mine. The test method involved the use of sampling filters exposed to natural radon daughters in air filtered by the test respirators. Respirators with a filtration efficiency high enough for them to be considered suitable for use against toxic dusts generally reduced radon daughter levels by 90% or more, though nuisance dust masks were ineffective. The measured penetration of radon daughters through the former types of filter correlated reasonably well with the penetration of 0.1 microns neutralized monodisperse aerosols, and with that of the BS 4400 sodium chloride aerosol, measured in the laboratory. To simulate exposure in working conditions mine air containing radon daughters was drawn through the test filters for 8 h, but their performance was not affected and they were not measurably radioactive as a result.