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., 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. A self-contained breathing apparatus may be open-circuit or closed-circuit, and open circuit units may be demand supplied or continuous-flow.
History As the fire service began to develop throughout the early 1800s, it became increasingly apparent that firefighters needed protection from the hazardous smoke and toxic gasses that were present when fighting fires. The earliest attempts at this included firefighters growing out long beards, dipping them in water, and then biting down on the beard while breathing through their mouth. The theory behind this was that the wet beard would act as some sort of filter for the smoke. Other early attempts included the French designed "Apparatus Aldini" which was an asbestos and woven wire mask which attempted to provide the user with a small amount of trapped clean air to breathe. In addition, there was an English-designed closed helmet that pumped clean air across a pane of glass to reduce breathing condensation.
Inspired by a fire accident they witnessed in a stable in England, the brothers Charles and John Deane designed and patented a "Smoke Helmet" to be used by firemen in smoke-filled areas in 1823. The apparatus comprised a copper helmet with an attached flexible collar and garment. A long leather hose attached to the rear of the helmet was to be used to supply air - the original concept being that it would be pumped using a double bellows. A short pipe allowed air to escape, as more was pumped in. The user breathed from the airflow as it passed the face. The garment was made of leather or airtight cloth, secured by straps. The first successful diving helmet was developed from this by Augustus Siebe, of London. An early firefighting breathing apparatus was designed by James Braidwood. Around 1825, he invented a mask that was connected to a long hose which was supplied with fresh air from a fire engine. A whistle was also attached to the mask for communications. This could be considered to be one of the first attempts of a PASS or Personal Alert Safety System device. Paul Hashagan also notes that, in 1863, A. Lacour developed and patented the "improved breathing apparatus". This system provided air to the wearer from two canvas and rubber balloon-like bags which were carried on the wearer's back. A pair of bellows would then allow the wearer to pump air to a mouthpiece. The firefighter would also wear goggles and a nose plug to provide further protection from the smoke and heat. Throughout the 1800s, other SCBA-like devices were developed by various people including a closed-circuit rebreather designed by Bernhard Draeger. The closed circuit system developed by him would not only be used by many fire departments, but also was one of the first working SCUBA systems. 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.
Types
Closed-circuit
The closed-circuit type, also known as a rebreather, 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. 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. 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. 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.
2015 ANSI definition ANSI Z88.2–2015 provides some background information on SCBAs in Annex A, 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".
Open-circuit
As of 1987, under 30 CFR 11
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