Principles of physiology and respirator performance

Several respirator performance criteria are set to satisfy the physiological requirements of the worker. In particular, Ve and PFI must be understood and used appropriately in the design process. Filtration principles and the nature of workplace aerosols must also be understood to determine appropriate test conditions for particulate respirator filters. Current filter test criteria assure that significant aerosol penetration will not occur in the workplace. It is unlikely that existing positive-pressure respirators can assure positive pressure in the breathing zone at all times for all wearers. High, unsustainable work rates and activities such as running in place have been shown to cause negative-pressure excursions under laboratory and workplace conditions. Because these excursions are brief and infrequent for today's respirators, both logic and performance measurements indicate they have a negligible effect on exposure. Filters could no doubt be designed to pass extreme test criteria. Similarly, it may be possible to design positive-pressure respirators to maintain positive pressure 100 percent of the time for all users. However, it is likely that cost and size would increase and comfort could decrease. Further, available evidence demonstrates that today's respirators provide their expected level of protection when properly selected, used, and maintained. As such, there is no demonstrated need for radical design changes.