A Guide to Atmosphere-Supplying Respirators 

Atmosphere-supplying respirators provide clean breathing air from a source independent of the work area. 

These respirators will protect wearers from many types of airborne contaminants (particles, gases, and vapors) 

and, in certain cases, oxygen-deficient atmospheres. There are three types of atmosphere-supplying respirators: 

supplied-air respirators (SARs), self-contained breathing apparatus (SCBAs), and combination SARs/SCBAs. 

Respirators need to be approved by the National Institute for Occupational Safety and Health (NIOSH) 

Respirator Approval Program and used in the context of a complete respiratory protection program per the 

Occupational Safety and Health Administration (OSHA) regulation 29 CFR 1910.134, which includes annual 

fit testing for all respirators with a tight-fitting facepiece.1 

Supplied-Air Respirators 

SARs are connected by an airline hose to a free-standing cylinder of breathing 

air, an air compressor, or a system supplying breathing air through the 

building. They are sometimes referred to as airline respirators. At a minimum, 

the breathing air must meet the requirements for Grade D breathing air.2

 They 

can be lightweight and used for long, continuous periods in atmospheres that are 

not immediately dangerous to life and health (IDLH).3

 However, a disadvantage 

of the SAR is that the respirator user’s mobility is limited by the length of the 

air supply hose. 

SARs deliver air to the user in multiple configurations including 

continuous-flow, demand, or pressure-demand. Continuous-flow SARs maintain 

airflow at all times. Demand and pressure-demand systems provide air based on the user’s breathing. Demand 

systems will cause negative pressure in the facepiece during inhalation. Pressure-demand systems maintain a 

positive pressure within the facepiece during use, which means that if leakage occurs, the airflow should be 

directed outward. 

Supplied-air respirators are available in configurations with hoods and helmets as well as tight-fitting facepieces. 

When utilized within a respiratory protection program, SARs generally have high assigned protection factors 

(APF), according to OSHA. A respirator’s APF is the minimum level of respiratory protection it is expected 

to provide when used as part of a workplace respiratory protection program. A respirator with a higher APF 

number gives better protection: an APF of 10 means that 1/10 of a contaminant outside the facepiece might be 

inhaled and an APF of 1,000 means that 1/1,000 of a contaminant outside the facepiece might be inhaled. 

Photo courtesy of Honeywell International Inc. 

1

 Refer to OSHA 29 CFR 1910.134(f)(8) for atmosphere supplying respirator ft test requirements. 2

 Compressed breathing air must meet at least the requirements for Type 1 - Grade D breathing air described in ANSI/CGA G-7.1-1989 

3 Table of IDLH values 4 Te 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. Tis level of performance can best be demonstrated by performing a workplace protection factor (WPF) or simulated workplace protection factor (SWPF) study or equivalent 

testing. Absent such testing, all other SARs with helmets/hoods are to be treated as loose-ftting facepiece respirators, and receive an APF of 25. (29 CFR 1910.134(d)(3)(i)(A)) 
Self-Contained Breathing Apparatus 

SCBAs are equipped with their own breathing air supply. Because of the portable air cylinder, unrestricted 

movement is an advantage of SCBAs. However, the limited service life makes them unsuitable for routine use for 

long, continuous periods. Te length of service life depends on the SCBA type. 

SCBAs are categorized as open-circuit and closed-circuit devices and can be used for entry into and escape from 

atmospheres that are considered IDLH or oxygen defcient. 

Open-Circuit SCBAs 

Open-circuit SCBAs are usually equipped with a full facepiece and contain their 

own breathing air supply in a pressurized cylinder that is worn on the back 

of the user. Typically, this is the type of respirator worn by frefghters. Tese 

respirators exhaust exhaled air into the atmosphere instead of recirculating it. 

Since there is no recirculation of breathing air, the service life of the open-circuit 

SCBA is usually shorter than a closed-circuit device. Open-circuit SCBAs have 

a service life of up to 75 minutes. Tere are two types of open-circuit SCBAs, 

demand and pressure demand. Te demand-type respirator only allows air into 

the facepiece as needed by the user. A demand-type open-circuit SCBA should 

not be used in IDLH atmospheres. 

Te pressure demand-type respirator is designed to maintain positive pressure Photo courtesy of 3M Scott in the facepiece at all times. 

Closed-Circuit SCBAs 

Another name for a closed-circuit SCBA is a “rebreather” device. Te breathing gas is recycled afer 

going through a process to remove the exhaled carbon dioxide and replace the oxygen consumed by the user. 

Closed-circuit SCBAs are approved for both entry and escape, or escape only. Entry and escape devices have a 

duration of one to four hours. Tey are designed for use in oxygen defcient and/or IDLH atmospheres such as 

those that might be encountered in mine rescues or confned spaces. 

Escape-only closed-circuit SCBAs, known as closed-circuit escape respirators 

(CCERs), are used in certain industrial and other work settings during emergencies to allow users to escape from IDLH or oxygen defcient environments. Te 

duration of a CCER is dependent on two things: (1) the total amount of oxygen 

available to the user (i.e., capacity) and (2) the oxygen consumption rate. CCERs are 

also known in the mining community as self-contained self-rescuers (SCSRs), and 

in other industries as emergency escape breathing devices (EEBDs) or apparatus 

(EEBAs). 

CCER, Photo courtesy of Ocenco 
Self-Contained Breathing Apparatus (continued) 

An SCSR is similar in design to the entry and escape closed-circuit SCBAs, but is 

considerably smaller and weighs less. Because it is an escape-only device, this type 

of CCER can only be used for up to one hour. 

SCSR, Photo courtesy of CSE 

Combination Supplied-Air/Self-Contained Breathing Apparatus 

A combination SAR/SCBA incorporates a backup self-contained 

air supply. Te self-contained portion of the device is only used 

when the primary air supply fails or becomes interrupted. Typically, 

the self-contained air supply is small, since it only needs to supply 

enough air to safely escape from a hazardous environment. Due to 

the typical short service life of the self-contained breathing air 

supply, these combination units are generally used for emergency 

escape from IDLH atmospheres. In certain circumstances, when 

larger air cylinders are used, entry into an IDLH environment is 

permitted, provided no more than 20% of the rated air supply is 

needed for entry. Photo courtesy of 3M Scott 

References 

NIOSH [1987]. NIOSH Guide to Industrial Respiratory Protection. Cincinnati, OH: U.S. Department of Health and Human Services, 

Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS 

(NIOSH) Publication No. 87-116, https://www.cdc.gov/niosh/docs/87-116/ 

OSHA [1998] 29 CFR 1910.134 Respiratory Protection. Washington, DC: U.S. Department of Labor, Occupational Safety and Health 

Administration, https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=12716 

Suggested Citation 

NIOSH [2019]. A Guide to Atmosphere-Supplying Respirators. By Cichowicz, J., Cofey, C., and Fries, M. Pittsburgh, PA: U.S. 

Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and 

Health. DHHS (NIOSH) Publication No. 2019-174, https://doi.org/10.26616/NIOSHPUB2019174

Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health, Centers 

for Disease Control and Prevention. 

This document is in the public domain 

and may be freely copied or reprinted. 

https://doi.org/10.26616/NIOSHPUB2019174 

DHHS (NIOSH) Publication No. 2019-174 

September 2019 

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