What to know
- Atmosphere-supplying respirators (ASRs) provide clean breathing air from a source independent of the work area.
- ASRs provide protection from many types of airborne contaminants, and in certain cases, oxygen-deficient atmospheres.
- There are three types of ASRs: supplied-air respirators (SARs), self-contained breathing apparatus (SCBAs), and combination SARs/SCBAs.
- Tight-fitting ASRs require fit testing.
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.
SARs can be lightweight and used for long, continuous periods in atmospheres that are not immediately dangerous to life and health (IDLH).1 However, mobility is limited by the length of the air supply hose.
Supplied-air respirators are available in configurations with hoods and helmets as well as tight-fitting facepieces.
Self-contained breathing apparatus
SCBAs are equipped with their own breathing air supply. Because of the portable air cylinder, movement is unrestricted. However, their limited service life makes them unsuitable for routine use for long, continuous periods. The length of service life depends on the SCBA type.
SCBAs are categorized as open-circuit and closed-circuit devices. They can be used for entry into and escape from IDLH or oxygen deficient atmospheres.
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 your back. Typically, firefighters wear this type of respirator.
Open-circuit SCBAs have a service life of up to 75 minutes. There are two types of open-circuit SCBAs, demand and pressure demand.
The demand-type respirator only allows air into the facepiece as you need it. This type should not be used in IDLH atmospheres. The pressure demand-type respirator is designed to maintain positive pressure in the facepiece at all times.
Closed-circuit SCBAs
Closed-circuit SCBAs are also known as "rebreather" devices. The breathing gas is recycled after going through a process to remove the exhaled carbon dioxide and replace the oxygen you consume.
Closed-circuit SCBAs are approved for entry and escape or escape only.
- Entry and escape devices have a duration of one to four hours. They are designed for use in oxygen deficient or IDLH atmospheres such as those that might be encountered in mine rescues or confined 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 you to escape from IDLH or oxygen deficient environments.
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). An SCSR is an escape-only device, so it can only be used for up to one hour.
Combination SAR/SCBA
A combination SAR/SCBA incorporates a backup self-contained air supply. The self-contained portion of the device is only used when the primary air supply fails or becomes interrupted.
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.
Resources
- Table of IDLH values
- NIOSH Approved is a certification mark of the U.S. Department of Health and Human Services (HHS) registered in the United States and several international jurisdictions.