An SCBA typically has three main components: a high-pressure tank (e.g., 2200 psi to 4500 psi), a pressure regulator, and an inhalation connection (mouthpiece, mouth mask or face mask), connected together and mounted to a carrying frame.
There are two kinds of SCBA: open circuit and closed circuit.
The closed-circuit type filters, supplements, and recirculates exhaled gas: see rebreather for more information. 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:-
Examples of modern rebreather SCBAs are
Open-circuit industrial breathing sets are filled with filtered, compressed air, the same air we breathe normally. The compressed air passes through a regulator, is inhaled by the user, then exhaled out of the system, quickly depleting the supply of air. Most modern SCBAs are open-circuit.
An open-circuit rescue or firefighter SCBA has a full-face mask, regulator, air cylinder, cylinder pressure gauge, and a harness with adjustable shoulder straps and waist belt which lets it be worn on the back. The air cylinder usually comes in one of three standard sizes: 30, 45 or 60 minutes. The relative fitness, and especially the level of exertion of the wearer, often results in variations of the actual usable time that the SCBA can provide air, often reducing the working time by 25% to 50%.
Air cylinders are made of aluminium, steel, or of a composite construction (usually carbon-fiber wrapped.) The composite cylinders are the lightest in weight and are therefore preferred by fire departments (UK: 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 3 years for composite cylinders, and every 5 years for metal cylinders. 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.
Open circuit SCBA will be either "positive pressure" or "negative pressure" operation.
There are two major application areas for SCBA, fire fighting, and industrial use.
For fire fighting, the design emphasis is on heat and flame resistance above cost. SCBA designed for fire fighting 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 fire fighter.
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 industial 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.
In the USA, 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 2002. 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. See NIOSH Approved SCBAs
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 fire fighting. 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.
The Royal Australian Navy uses the Open Circuit Compressed Air Breathing Apparatus (OCCABA), a backpack-style, positive pressure breathing apparatus, for fire-fighting roles.
Siebe Gorman produced these makes of open-circuit SCBA units:
All these initials mean the same type of open-circuit equipment.
An SCBA unit may also be referred to as a "Scott Pack", deriving the name of the Scott company that manufactures many SCBAs.