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 Photo courtesy of Honeywell International Inc.
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.

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 emergen-
cies 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

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