Supplied Air Systems

per OSHA website http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=12716&p_table=standards

Assigned Protection Factors (APFs) Employers must use the assigned protection factors listed in Table 1 to select a respirator that meets or exceeds the required level of employee protection. When using a combination respirator (e.g., airline respirators with an air-purifying filter), employers must ensure that the assigned protection factor is appropriate to the mode of operation in which the respirator is being used.
 

Table 1. -- Assigned Protection Factors⁵

Type of respirator1, 2	Quarter mask	Half mask	Full facepiece	Helmet/ hood	Loose-fitting facepiece
1. Air-Purifying Respirator	5	310	50	..............	..............
2. Powered Air-Purifying Respirator (PAPR)	..............	50	1,000	425/1,000	25
3. Supplied-Air Respirator (SAR) or Airline Respirator     • Demand mode     • Continuous flow mode     • Pressure-demand or other positive-pressure mode	.............. .............. ..............	10 50 50	50 1,000 1,000	.............. 425/1,000 ..............	.............. 25 ..............
4. Self-Contained Breathing Apparatus (SCBA)     • Demand mode     • Pressure-demand or other positive-pressure mode (e.g., open/closed circuit)	.............. ..............	10 ..............	50 10,000	50 10,000	.............. ..............

Notes:
¹Employers may select respirators assigned for use in higher workplace concentrations of a hazardous substance for use at lower concentrations of that substance, or when required respirator use is independent of concentration.
²The assigned protection factors in Table 1 are only effective when the employer implements a continuing, effective respirator program as required by this section (29 CFR 1910.134), including training, fit testing, maintenance, and use requirements.
³This APF category includes filtering facepieces, and half masks with elastomeric facepieces.
⁴The employer must have evidence provided by the respirator manufacturer that testing of these respirators demonstrates performance at a level of protection of 1,000 or greater to receive an APF of 1,000. This level of performance can best be demonstrated by performing a WPF or SWPF study or equivalent testing. Absent such testing, all other PAPRs and SARs with helmets/hoods are to be treated as loose-fitting facepiece respirators, and receive an APF of 25.
⁵These APFs do not apply to respirators used solely for escape. For escape respirators used in association with specific substances covered by 29 CFR 1910 subpart Z, employers must refer to the appropriate substance-specific standards in that subpart. Escape respirators for other IDLH atmospheres are specified by 29 CFR 1910.134 (d)(2)(ii).

end of OSHA website excerpt.