Respiratory Protection Equipment Air Movement Source

Types of Air Movement Sources

The user's inspiratory effort is the air movement source, pulling ambient air through filters during each inhalation, which depends completely on the worker's lung capacity and physical effort, and any facial seal leak allows unfiltered air to enter, especially during high inhalation rates 1, 2, 3.
Small electric motors actively drive air through HEPA filters, eliminating the dependence on the user's inspiratory effort, and generate air flows that generally exceed expected inhalation rates, creating positive pressure inside the face piece, which reduces facial seal leaks to less than 2% with fitted face pieces and less than 4% with loose hoods or helmets, compared to 0-20% in negative pressure respirators 1, 2, 3, 6, 7.

The CDC and NIOSH recommend PAPR with HEPA filters (motorized source) for aerosol-generating procedures and isolation rooms, where administrative and engineering controls may be insufficient, and PAPR with hoods have been specifically recommended for organophosphorus nerve agents and chemical-biological threats 1, 2, 3, 6, 8.
A common PAPR with hood achieved a protection factor of 20,000 in government tests, compared to factors of 10-100 for negative pressure respirators, and the American College of Occupational and Environmental Medicine recommends PAPR for workers with facial hair, where negative pressure respirators lose effectiveness up to 330 times 1, 2, 6, 7.

For high-risk biological agents, PAPR with HEPA filters (motorized source) are recommended, and for routine use, N95 respirators (inspiratory effort source) are acceptable when there is adequate facial fit verified by formal testing, but the filter efficiency is effectively 100%, so all particle leakage occurs at the facial seal, making the air movement source critical 3, 7, 8.
The National Institute for Occupational Safety and Health recommends that workers with facial hair use PAPR or undergo complete shaving, as negative pressure respirators are useless with facial hair, and the Centers for Disease Control and Prevention recommend that employers not rely solely on filter efficiency, as facial seal leaks are the critical point of failure in negative pressure respirators 1, 3, 7.