SCBA - Self Contained Breathing Apparatus 3
SCBA - Self Contained Breathing Apparatus 3 : Open-Circuit: A person wearing an MSA Brand breathing mask with a Nomex hood on. This face piece attaches with a regulator to form a full SCBA. SCBA packs carried on a rack in a firetruck for underwater open-circuit breathing sets see Scuba set#Types. Open-circuit industrial breathing sets are filled with filtered, compressed air, rather than pure oxygen. Typical open-circuit systems have two regulators; a first stage to reduce the pressure of air to allow it to be carried to the mask, and a second stage regulator to reduce it even further to a level just above standard atmospheric pressure. This air is then fed to the mask via either a demand valve (activating only on inhalation) or a continuous positive pressure valve (providing constant airflow to the mask). An open-circuit rescue or firefighter SCBA has a fullface 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: 4 liter, 6 liter, or 6. 8 liter. The duration of the cylinder can be calculated to Size of cylinder X Pressure / by 40 and then less 10 minutes because of a safety margin. so a 6 liter cylinder, of 300bar, is 6 X 300 / 40 - 10 = 35minutes working duration 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%. SCBA apparatus with PASS device (ADSU). Air cylinders are made of aluminium, steel, or of a composite construction (usually carbon-fiberwrapped). 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 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
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