Self-contained breathing apparatus

Self-contained breathing apparatus
Self-contained breathing apparatus
Other name(s)	SCBA, compressed air breathing apparatus, breathing apparatus
Regulated by	National Institute for Occupational Safety and Health, National Fire Protection Association
Regulation	42 CFR 84, EN 137, NFPA 1981
NIOSH schedule	TC-13F
	[edit on Wikidata]

A self-contained breathing apparatus (SCBA) is a respirator worn to provide an autonomous supply of breathable gas in an atmosphere that is immediately dangerous to life or health from a gas cylinder.^[1] They are typically used in firefighting and industry. The term self-contained means that the SCBA is not dependent on a remote supply of breathing gas (e.g., through a long hose). They are sometimes called industrial breathing sets. Some types are also referred to as a compressed air breathing apparatus (CABA) or simply breathing apparatus (BA). Unofficial names include air pack, air tank, oxygen cylinder or simply pack, terms used mostly in firefighting. If designed for use under water, it is also known as a scuba set (self-contained underwater breathing apparatus).

An open circuit SCBA typically has three main components: a high-pressure gas storage cylinder, (e.g., 2,216 to 5,500 psi (15,280 to 37,920 kPa), about 150 to 374 atmospheres), a pressure regulator, and a respiratory interface, which may be a mouthpiece, half mask or full-face mask, assembled and mounted on a framed carrying harness.^[2]

A self-contained breathing apparatus may fall into one of three categories: open-circuit, closed-circuit,^[3] or continuous-flow.^[4]

Types

Closed-circuit

The closed-circuit type, also known as a rebreather,^[5] operates by filtering, supplementing, and recirculating exhaled gas. It is used when a longer-duration supply of breathing gas is needed, such as in mine rescue and in long tunnels, and going through passages too narrow for a big open-circuit air cylinder. Before open-circuit SCBA's were developed, most industrial breathing sets were rebreathers, such as the Siebe Gorman Proto, Siebe Gorman Savox, or Siebe Gorman Salvus.^{[citation needed]} An example of modern rebreather SCBAs would be the SEFA.

As of 1987, under 30 CFR 11

Duration of closed-circuit SCBAs is somewhere between 1-4 hours. A closed-circuit SCBA system is negative-pressure, increasing the risk of leaks.^[5]

There are two types of closed-circuit SCBA according to NIOSH:

Uses compressed oxygen.
Uses an oxygen-generating solid. This involves a chemical reaction between potassium superoxide with exhaled water and carbon dioxide. A chlorate candle has to be struck to start the device.

To reduce pressure buildup from use, a pressure-relief valve with saliva trap is included. Closed-circuit SCBAs are also noticeably smaller than open-circuit ones.^[5]

Self-contained self-rescue devices are also closed-circuit SCBAs, working on the same principles, being designed for emergency use in mines, and lasting about one hour.^[5]

Open-circuit

As of 1987, under 30 CFR 11

An open-circuit SCBA does not recirculate air; it instead allows respired air to be exhausted outside. While 30 CFR 11 does not restrict the gas that can be used (although compressed air is usually chosen), use of compressed oxygen is not allowed due to the system's exposure to outside air. Duration is usually limited to 30-60 minutes.^[6]

There are two types of open-circuit SCBA according to NIOSH:

Demand: 2000 psi to the regulator from the main valve, plus a bypass valve in case of failure, with a two-stage regulator reducing pressure to 50-100 psi.
Pressure-Demand: Similar to demand, but with a spring in the diaphragm, which holds the admission valve open, for continuous air flow to the facepiece.

NIOSH emphasizes that facepieces between both SCBA types cannot be interchanged, but certain SCBAs can be switched to both 'demand' and 'pressure-demand' operation. However, both modes require different training.^[6]

Common traits

Open-circuit industrial breathing sets are filled with filtered, compressed air. Typical open-circuit systems have two stage regulators. The first stage reduces the pressure from storage pressure of up to more than 300 bar to about 10 bar for supply to the second stage on the mask, which further reduces it to just above atmospheric pressure via a demand valve when the pressure drops on inhalation. A positive pressure mask has the demand valve set to close when the pressure inside the mask is slightly above the external ambient pressure, so when the mask is removed from the face or leaks around the skirt, the demand valve will free-flow.^{[citation needed]}

An open-circuit rescue or firefighting SCBA has a full-face mask, also called the face-piece, a demand regulator, air cylinder, pressure gauge, (sometimes with an integrated PASS device), and a harness with adjustable shoulder straps and waist belt which lets it be worn on the back. The air cylinder is commonly 4 liter, 6 liter, or 6.8 liter, but other sizes are also available. The endurance of the cylinder can be calculated from the volume, pressure and breathing rate of the user. The formula: volume (in liters) × pressure (in bars) / 40 (litres per minute) - 10 minutes (the 10 minutes is a safety margin, or reserve), so a 6-liter cylinder, of 300 bar, is 6 × 300 / 40 - 10 = 35 minutes working duration. The fitness and level of exertion of the wearer affect breathing rate, and result in variations of the actual usable time of the SCBA.^{[citation needed]}

Air cylinders are made of aluminium, steel, or of a composite construction (usually glass or carbon-fiber wrapped.) The composite cylinders are the lightest in weight and are therefore preferred by fire departments (UK: fire and rescue services previously called fire brigades), but they also have the shortest lifespan and must be taken out of service after 15 years. Air cylinders must be hydrostatically tested every 5 years.^{[clarification needed]} During extended operations, empty air cylinders can be quickly replaced with fresh ones and then refilled from larger tanks in a cascade storage system or from an air compressor brought to the scene.^{[citation needed]}

Continuous-flow

Escape SCBAs, also known as ESCBAs, come with hoods, are meant for escapes only, and are operated in continuous flow mode.^[7]^[4]^[8]

Escape only SCBAs, designed for escape from IDLH situations, regardless of type, are usually limited to 3-10 minutes.^[6]^{[clarification needed]}

Differences under 42 CFR 84

42 CFR 84 replaces the 30 CFR 11 respirator regulation used by NIOSH. As of 2001, quality assurance of SCBA harnesses is required. Labels have been updated to remove MSHA emblems from respirator labels, as MSHA is no longer involved in respirator approval except for respirators approved for mining. As a result, new SCBAs now have to specify whether the SCBA is "intended for mine use".^[9]

Updated SCBA labels under 42 CFR 84

Part 84 SCBA respirator label
Harness label
Scrubber label

Facepiece

SCBAs usually come with full-facepieces,^[7] but can also come with half-mask or mouthpiece in demand or pressure-demand mode, though use of mouthpieces are limited to escapes only, as of 1987.^[4]

Hoods and helmets are limited to continuous flow mode only, and are also used in air-line respirators in addition to escape-only SCBAs.^[4]^[8]

Usage

There are two major application areas for SCBA: firefighting, and industrial use in confined spaces.^[10]

For firefighting, the design emphasis is on heat and flame resistance above cost. SCBAs designed for firefighting tend to be expensive because of the exotic materials used to provide the flame resistance, and to a lesser extent, to reduce the weight penalty on the firefighter. In addition, modern firefighting SCBAs incorporate a PASS device (personal alert safety system) or an ADSU (automatic distress signal unit) into their design. These units emit distinctive, high-pitched alarm tones to help locate firefighters in distress by automatically activating if movement is not sensed for a certain length of time (typically between 15 and 30 seconds), also allowing for manual activation should the need arise. In firefighting use, the layout of this breathing set should not interfere with ability to carry a rescued person over the firefighter's shoulders.^{[citation needed]}

The other major application is for industrial users of various types. Historically, mining was an important area, and in Europe this is still reflected by limitations on use in the construction of SCBAs of metals that can cause sparks. Other important users are petrochemical, chemical, and nuclear industries. The design emphasis for industrial users depends on the precise application and extends from the bottom end which is cost critical, to the most severe environments where the SCBA is one part of an integrated protective environment which includes gas-tight suits for whole-body protection and ease of decontamination. Industrial users will often be supplied with air via an air line, and only carry compressed air for escape or decontamination purposes.^{[citation needed]}

Other regulations and standards

In the United States and Canada, SCBAs used in firefighting must meet guidelines established by the National Fire Protection Association, NFPA Standard 1981. If an SCBA is labeled as "1981 NFPA compliant", it is designed for firefighting. The current version of the standard was published in 2018.^[11] These standards are revised every five years. Similarly, the National Institute for Occupational Safety and Health (NIOSH) has a certification program for SCBA that are intended to be used in chemical, biological, radiological, and nuclear (CBRN) environments.

Any SCBA supplied for use in Europe must comply with the requirements of the Personal Protective Equipment Directive (89/686/EEC). In practice this usually means that the SCBA must comply with the requirements of the European Standard EN 137:2006. This includes detailed requirements for the performance of the SCBA, the marking required, and the information to be provided to the user. Two classes of SCBA are recognised, Type 1 for industrial use and Type 2 for firefighting. Any SCBA conforming to this standard will have been verified to reliably operate and protect the user from -30 °C to +60 °C under a wide range of severe simulated operational conditions.

Human factors

SCBA is intended to be personal protective equipment, but its use is not without cost. The weight of the unit and work of breathing affect the work capacity and agility of the wearer, and the full-face mask, while protecting the face and eyes from heat, smoke, and toxic gases, also reduces peripheral vision and awareness of the surroundings. The weight and harness straps may limit tidal volume, ventilation rate, and oxygen consumption, and heart rate may increase in comparison with the same exercise levels without the equipment. Shoulder harness straps of heavy SCBA can reduce free motion of the thorax which affects breathing.^[12]

Notes

^ Bollinger 1987, p. 184
^ IFSTA 2008, p. 190.
^ IFSTA 2008, p. 191.
^ ^a ^b ^c ^d Bollinger 1987, pp. 7–8
^ ^a ^b ^c ^d Bollinger 1987, pp. 55–56
^ ^a ^b ^c Bollinger 1987, pp. 59–64
^ ^a ^b Bollinger 1987, p. 207
^ ^a ^b Bollinger 1987, p. 65
^ "STANDARD APPLICATION PROCEDURES FOR THE CERTIFICATION OF RESPIRATORS" (PDF). NIOSH. January 2001. Archived from the original (PDF) on 2003-03-19.
^ Bollinger 1987, p. 120
^ "NFPA". NFPA. Archived from the original on 6 April 2018. Retrieved 5 May 2018.
^ Louhevaara, V.; Smolander, J.; Tuomi, T.; Korhonen, O.; Jaakkola, J. (1985). "Effects of an SCBA on breathing pattern, gas exchange, and heart rate during exercise". J Occup Med. 27 (3): 213–216. PMID 3981278.

References

IFSTA (2008). Essentials of Fire Fighting and Fire Department Operations (5th ed.).
Bollinger, Nancy J. (1987). NIOSH Guide to Industrial Respiratory Protection.

External links

[1] Bollinger 1987, p. 184

[FOOTNOTEIFSTA2008190-2] IFSTA 2008, p. 190.

[FOOTNOTEIFSTA2008191-3] IFSTA 2008, p. 191.

[hoodhelmetmouth-4] Bollinger 1987, pp. 7–8

[fivesix-5] Bollinger 1987, pp. 55–56

[open-6] Bollinger 1987, pp. 59–64

[twoseven-7] Bollinger 1987, p. 207

[scbaescape-8] Bollinger 1987, p. 65

[9] "STANDARD APPLICATION PROCEDURES FOR THE CERTIFICATION OF RESPIRATORS" (PDF). NIOSH. January 2001. Archived from the original (PDF) on 2003-03-19.

[10] Bollinger 1987, p. 120

[11] "NFPA". NFPA. Archived from the original on 6 April 2018. Retrieved 5 May 2018.

[Louhevaara_et_al_1985-12] Louhevaara, V.; Smolander, J.; Tuomi, T.; Korhonen, O.; Jaakkola, J. (1985). "Effects of an SCBA on breathing pattern, gas exchange, and heart rate during exercise". J Occup Med. 27 (3): 213–216. PMID 3981278.

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Self-contained breathing apparatus

Types

Closed-circuit

As of 1987, under 30 CFR 11

Open-circuit

As of 1987, under 30 CFR 11

Common traits

Continuous-flow

Differences under 42 CFR 84

Facepiece

Usage

Other regulations and standards

Human factors

See also

Notes

References

Further reading

External links