Self-contained breathing apparatus

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. 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. 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., , 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.

A self-contained breathing apparatus may be open-circuit or closed-circuit, and open circuit units may be demand supplied or continuous-flow.

thumb|right|1842 sketch of the [[Charles Anthony Deane|Deane brothers' diving helmet, the first surface-supplied diving dress equipment in the world.]] Inspired by a fire accident they witnessed in a stable in England, Other devices included the Gibbs which was approved for use in 1920 and was developed by MSA and the Proto, which was developed by the London-based company Siebe Gorman.

Close to the mid-1900s and post WWII, Scott Aviation began developing an SCBA designed specifically for firefighting use. The first SCBA designed by Scott was called the AirPac and introduced in 1945. This was the first version of the modern SCBA as we know it today. As the space race continued throughout the 1900s, SCBA technology would continue to improve allowing the SCBAs to become less cumbersome and for firefighters to carry less weight and more air.

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. which is current and approved as of March 2015. Closed circuit SCBAs scrub carbon dioxide with a chemical; Z88.2 notes sodium hydroxide as an example of one such chemical.

A "demand SCBA", according to the standard, is where "the facepiece is negative during inhalation". Whereas if the facepiece is positive during inhalation, it is a "pressure-demand SCBA". Regardless of the type of closed-circuit SCBA, the duration of closed-circuit SCBAs is, according to Z88.2, between "15 minutes to 4 hours".

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.

Common traits

thumb|left|upright=0.8|SCBA pack with [[PASS device (ADSU)]]

Continuous-flow

Escape SCBAs, also known as ESCBAs, are intended for escape from IDLH situations only, and when fitted with hoods are operated in continuous flow mode. As a result, new SCBAs now have to specify whether the SCBA is "intended for mine use".

Facepiece

SCBAs usually come with full-facepieces, 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.

Usage

thumb|Elastomeric masks linked to backpack air tanks: self-contained breathing apparatus, worn by firefighters advancing with a [[firehose.]]

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

For SCBAs used in firefighting, manufacturers typically prioritize fire resistance and weight reduction over cost. SCBAs used by the fire service also incorporate other features such as a PASS (personal alert safety system), which is a device that emits a loud alarm should the firefighter manually activate it or remain motionless for a certain amount of time. Other features may include Bluetooth connection to voice amplifiers or portable radios, digital heads-up displays, built-in infrared cameras, ePAR (electronic personal accountability report) system, point of view video recording, and digital screens allowing the firefighter to more easily check their air supply. Every SCBA used in the fire service also comes with a vibralert system which alerts the firefighter as they get low on air

SCBAs are also used in a variety of industrial settings including mining, petrochemical, chemical, and nuclear industries. In some of the most hazardous conditions, SCBAs can be worn in conjunction with gas tight suits, which also aids in decontamination procedures. In the industrial setting, especially in confined spaces, a user will often be supplied air through a pressurized airline and will only carry compressed air cylinders for emergency escape and decontamination.

Other regulations and standards

thumb|left|Volunteer fire fighter exiting live burn structure wearing NIOSH-certified SCBA, NFPA compliant turn-out gear, and holding a pike pole

thumb|left|Example NFPA 1981 regulatory label

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. 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.

References

Works cited

External links

Air specification chart – an explanation for "Grade D" air
CBRN SCBA interim user guide and list of approved CBRN SCBA (Archived)
CBRN SCBA standard development and publication leading to the first NIOSH-Certified SCBA with CBRN protection offered by the US DHHS/CDC/NIOSH/NPPTL on June 3, 2002 (Archived)
Image of 2-cylinder open-circuit SCBA
Study of the physiological effects of wearing breathing apparatus by RG Love and others. Institute of Occupational Medicine Research Report TM/94/05