Self-contained breathing apparatus

A self-contained breathing apparatus (дыхательный аппарат автономного действия) or SCBA, sometimes referred to as a Compressed Air Breathing Apparatus (CABA) or simply Breathing Apparatus (BA) is a device worn by rescue workers, firefighters, and others to provide breathable air in a hostile environment (в опасной для органов дыхания среде). When not used underwater, they are sometimes called industrial breathing sets. The term "self-contained" means that the breathing set is not dependent on a remote supply (e.g. through a long hose). If designed for use under water, it is called SCUBA (= self-contained underwater breathing apparatus).

A 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.

Closed-circuit SCBA

The closed-circuit type (тип замкнутой системы дыхательного аппарата) filters, supplements, and re-circulates 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 was developed, most industrial breathing sets were re-breathers not so efficient in use.

Open-circuit

Open-circuit industrial breathing sets are filled with filtered, compressed air, the same air we breathe normally. The compressed air passes through a regulator and is inhaled by the user, then the air is exhaled out of the system, quickly depleting the supply of air. Most modern SCBA 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 aluminum, steel, or of a composite construction. 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 system or from an air compressor brought to the scene.

Open circuit SCBA will be either "positive pressure" or "negative pressure" operation. A "negative pressure" SCBA may be used with a standard facemask instead of filter canisters, and air is delivered to the wearer when he breathes in, or in other words, reduces the pressure in the mask to less than outside pressure, hence the name "negative pressure". The limitations of this are obvious, as any leaks in the device or the interface between the mask and the face of the wearer would reduce the protection offered. "Positive pressure" SCBA is much more reliable. By careful design, the device is set to maintain a small pressure inside the face-piece. Although the pressure drops when the wearer breathes in, the device always maintains a higher pressure inside the mask than outside of the mask. Thus, even if the mask leaks slightly, there is a flow of clean air out of the device, automatically preventing inward leakage under most circumstances. Although the performance of both types of SCBA may be similar under optimum conditions, this "fail safe" behavior makes a "Positive pressure" SCBA preferable for most applications. As there is usually no air usage penalty in providing positive pressure, the older "Negative pressure" type is in most cases an obsolete configuration and is only seen with older equipment.

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 tends 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 of metals in the construction of SCBA that can cause sparks. Other important users are petrochemical, chemical and nuclear industries. The design emphasis for industrial users depends on the precise application in various situations ranging from simple ones 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 they only carry compressed air for escape or decontamination purposes.

In the USA, SCBA 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 is intended to be used in chemical, biological, radiological, and nuclear (CBRN) environments.

Any SCBA supplied for use in Europe must comply with the requirements (удовлетворять требованиям) 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. 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 recognized, Type 1 for industrial use and Type 2 for fire fighting. Any SCBA of 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.

Дата добавления: 2014-12-27