Field protection factor provided by a full-facepiece powered air-purifying respirator against asbestos dust

The acrylic facepiece visors of two Racal Breathe-Easy 7 full facepiece powered air-purifying respirators (PARR) were modified to allow the collection of air samples from within the respirator facepiece. Results of initial quantitative fit tests done in the laboratory prior to sample collection indicated fit factors if excess of 1,000 for each of the PARRs. Ten pairs of inside- and outside-facepeice air samples were collected on 0.8-um pore size polycarbonate filters while workers removed asbestos insulation from structures in two separate removal projects. The filter were analyzed by the investigator using the B counting rules of the NIOSH 7400 fiber counting method adapted for use with a scanning electron microscope. There was no significant difference in sample results obtained from the initial sample count and a subsequent count two weeks later. Protection Factors were calculated based on the results of the air sampling. Initial results indicated that the respirator provided a geometric mean protection factor of 44, which is far below the protection factor of 1,000 assigned to all PAPRs by OSHA and NIOSH. A subset of the sample was analyzed using the 7400 method's lower fiber size limit of 4-um and by counting all visible fibers. When only gibers greater than 5-um were counted, the geometric mean protection factor of the respirator was 53, while a geometric mean protection factor of 175 was calculated when all visible fibers were counted. This latter protection factor of 175 is believed to be more accurate representation of the respirator's performance, and is fairly consistent with the results of previous studies involving PARRs, Additional studies are needed on the subject of PAPR protection factors, and a single reference citing the results of actual workplace protection factor studies of different respirator types against different workplace contaminants should be developed.