WORKPLACE FIELD TESTING OF A DISPOSABLE NEGATIVE PRESSURE HALF-MASK DUST RESPIRATOR (3M 8710)

Abstract

The performance of the 3M 8710 dust/mist half-mask respirator was characterized in a workplace atmosphere that contained concentrations of manganese dioxide dust in the range 0.14 to 20 mg/m3 as manganese. Workplace protection factors (WPFs) were calculated from the simultaneously measured concentrations outside the respirator, Co, and inside the respirator, Ci. The WPFs, Co/Ci, were in the range 2.8 to 848. A plot of WPF versus Co indicated that for 1<Co<20 mg/m3, WPF did not have a constant value but tended to increase as Co increased. The relation could be approximated by the linear regression equation WPF=12.9+28.4 Co (r=0.77). In addition to measurements of Ci and Co, the size distribution of manganese dioxide particles was determined at different values of Co. The relation of Cp, the concentration of particles in stated particle-size groups, and Co was found to have the form Cp=A+kCo, where A and k are constants. A plausible explanation for the dependence of WPF on Co could be obtained by assuming that the performance of the respirator is related to particle size such that particles of small aerodynamic diameter (e.g., <2 µm) have a higher probability of penetrating into the respirator than do larger particles. With this assumption, WPF depends on Co if kCo, <<A, and is independent of Co if kCo, >>A. The explanation applies to particle penetration through either the filter medium or the face seal.