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]
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.
La duración de los SCBA de circuito cerrado oscila entre 1 y 4 horas. Un sistema SCBA de circuito cerrado tiene presión negativa, lo que aumenta el riesgo de fugas. [5]
Hay dos tipos de SCBA de circuito cerrado según NIOSH:
Para reducir la acumulación de presión por el uso, se incluye una válvula de alivio de presión con trampa de saliva. Los SCBA de circuito cerrado también son notablemente más pequeños que los de circuito abierto. [5]
Los dispositivos autónomos de autorrescate también son SCBA de circuito cerrado, funcionan según los mismos principios, están diseñados para uso de emergencia en minas y duran aproximadamente una hora. [5]
Un SCBA de circuito abierto no recircula aire; en cambio, permite que el aire respirado se expulse al exterior. Si bien 30 CFR 11 no restringe el gas que se puede usar (aunque generalmente se elige aire comprimido), no se permite el uso de oxígeno comprimido debido a la exposición del sistema al aire exterior. La duración suele limitarse a 30-60 minutos. [6]
Hay dos tipos de SCBA de circuito abierto según NIOSH:
NIOSH enfatiza que las piezas faciales entre ambos tipos de SCBA no se pueden intercambiar, pero ciertos SCBA se pueden cambiar a operación tanto de 'demanda' como de 'presión-demanda'. Sin embargo, ambos modos requieren una formación diferente. [6]
Los equipos de respiración industrial de circuito abierto están llenos de aire comprimido filtrado. Los sistemas típicos de circuito abierto tienen reguladores de dos etapas. La primera etapa reduce la presión de almacenamiento de hasta más de 300 bar a aproximadamente 10 bar para el suministro a la segunda etapa de la máscara, que la reduce aún más a justo por encima de la presión atmosférica a través de una válvula de demanda cuando la presión cae al inhalar. Una máscara de presión positiva tiene la válvula de demanda configurada para cerrarse cuando la presión dentro de la máscara está ligeramente por encima de la presión ambiental externa, de modo que cuando se quita la máscara de la cara o hay fugas alrededor del faldón, la válvula de demanda fluirá libremente. [ cita necesaria ]
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]
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]
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]
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There are two major application areas for SCBA: firefighting, and industrial use in confined spaces.[9]
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]
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.[10] 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.
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.[11]
