Abstract
Pressure-demand self-contained breathing apparatus (SCBA) respirators are designed to maintain a positive pressure inside the facepiece at all times and therefore provide a high degree of respiratory protection. However, under conditions of high exertion fire fighters may overbreathe their respirators and transiently develop negative facepiece pressures. For pressure-demand respirators, facepiece leakage requires both negative pressure excursions and poor facepiece fit. Tucson Fire Department (TFD) fire fighters were studied to determine if this overbreathing poses a potential health threat, and if quantitative respirator fit testing could improve fire fighter safety. TFD fire fighters wear SCOTT 4.5 unit pressure-demand SCBA. Controlled negative pressure (CNP) fit testing demonstrated low facepiece leakage (< 10 cc/min at–0.51 inches of water) in 78 percent of 102 TFD fire fighters and in 82 percent of 51 fire fighters fit for a large facepiece using a qualitative technique. The maximum leakage in a fire fighter fit for a large facepiece was 1530 cc/min. Treadmill testing of 10 fire fighters revealed that they all had facepiece negative pressure excursions (mean negative pressure 0.071 ± 0.024 inches of water; mean duration of negative pressure excursions 3.41 ± 2.04%). Application of the maximum measured negative pressure excursion during treadmill testing to the worst facepiece leakage rate measured during CNP fit testing resulted in a calculated protection factor of 4000. All other fire fighters fit for a large facepiece had a calculated protection factor of over 10,000. While not essential, CNP respirator fit testing can provide important information for fire fighters using pressure-demand SCBA.