"Worst Case" aerosol testing parameters: II. Efficiency dependence of commercial respirator filters on humidity pretreatment.
Am Ind Hyg Assoc J 1989 May; 50(5):265-270
Filter preconditioning recommendations offered by the American National Standards Institute (ANSI) were tested in this study. These recommendations called for the unprotected respirator filter media to be preconditioned in a 38 degree-C and 85 percent relative humidity (RH) environment for 24 hours prior to any testing of the efficiency of the media. The current study examined the efficiencies of filter materials following exposures of 1, 7, 14, 28 and 42 days to these preconditioning treatments. Tests were conducted using six resin impregnated wool felt filters using a 0.6 micrometer mass median aerodynamic diameter (MMAD) unneutralized sodium-chloride (NaCl) particle at a flow rate of 32 liters/minute. Additional studies of the same material used flow rates of 32 and 77 liters/minute. Other tests involved four different types of electrostatic filters using a monodispersed 0.3 micrometer diameter dioctyl-phthalate (DOP) aerosol and an NaCl aerosol with a 1.0 micrometer MMAD. Filter face velocities of 5.4 and 6.5 centimeters/second (cm/s) were used. Depending on the preconditioning time (1 to 42 days) a 2 to 6 percent drop in the efficiency of the electrostatic filters was demonstrated. High efficiency filters retained their level of operation, 99.97 percent effective, in spite of preconditioning. The particle size appears to be important in determining efficiency and perhaps has some interrelationship to humidity levels. The authors conclude that some degradation does occur in the efficiency of filter material following unprotected preconditioning when tested with a neutralized worst case aerosol. As it is not unreasonable to expect that filter material may well be stored under conditions such as these for some time, the fact that the efficiency deteriorates with time becomes important.
NIOSH-Author; Aerosol-particles; Climatic-conditions; Respiratory-protective-equipment; Equipment-reliability; Testing-equipment; Personal-protective-equipment; Filter-materials
American Industrial Hygiene Association Journal