Code of Federal Regulations Title 42. Public Health § 42.84.142 Air supply source;  hand-operated or motor driven air blowers;  Type A supplied-air respirators;  minimum requirements

(a) Blowers shall be designed and constructed to deliver an adequate amount of air to the wearer with either direction of rotation, unless constructed to permit rotation in one direction only, and to permit the free entrance of air to the hose when the blower is not operated.

(b) No multiple systems, whereby more than one user is supplied by one blower, will be approved, unless each hose line is connected directly to a manifold at the blower.