Cylinders and concentrators specifically, are especially designed to supply oxygen to patients at hospitals, home, on the go, or when they are being transferred between medical sites. The human body cannot sustain without the oxygen that we breathe in through the air.
invention of oxygen cylinder was one of the most important developments in the field of medical practice. Oxygen and other gases were compressed and stored at high pressure in seamless containers constructed from hand-forged steel in1880. Materials technology has continued to evolve and now medical gas cylinders are generally made of steel alloys or aluminum. The filling pressure as well as capacity has increased considerably while at the same time the weight of cylinders has reduced. Today oxygen cylinder of equivalent size holds a third more oxygen but weighs about 20 kg less. The cylinders are of varying sizes and are color coded. They are tested at regular intervals by the manufacturer using hydraulic, impact, and tensile tests. The top end of the cylinder is fitted with a valve with a variety of number and markings stamped on it. Common valve types include Pin index valve, bull nose, hand wheel and integral valve. The type of valve varies with cylinder size. Small cylinders have a pin index valve while large have a bull nose type. Safety features in the cylinder are Color coding, pin index, pressure relief device, Bodok seal, and label attached etc., Safety rules and guidelines must be followed during storage, installation and use of cylinders to ensure safety of patients, hospital personnel and the environment.
Keywords: Cylinders, installation of cylinders, medical and anesthetic gases, pin index safety system, safety devices, testing, valves
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Gas cylinder is a term that is commonly used to describe a pressurized container used for storage and transport. The gases used in anaesthesia are generally supplied under high pressure, either in cylinders or via pipeline with cylinders on anaesthesia machines for emergency backup. Oxygen, nitrous oxide, and medical air are usually supplied from pipeline. Entonox in some hospitals is also supplied via pipeline though it is more common to be supplied by portable cylinders. Bulk supply of oxygen in the hospitals is by cryogenic liquid system, liquid cylinder installation or from the oxygen concentrator. [1,2] Air is supplied either as pressurized cylinders or from compressors. Bulk production of oxygen is usually by fractional distillation of liquid air. In every country there are a series of regulations and standards for manufacture and the use of medical cylinders. While regulatory measures are designed to ensure safety in the manufacture and distribution of medical gases, sporadic accidents do occur [3] which have the potential to cause injury to patients, doctors or paramedic staff. Therefore, safety should be the highest priority.
Medical gas cylinders were traditionally constructed of low carbon steel. Now they are constructed of light weight chrome molybdenum steel, aluminum or a composite (such as aluminum wrapped in carbon fiber). Special cylinders made from aluminum are useful in magnetic resonance imaging (MRI) room. Typical wall thickness of steel cylinders is 3 mm and that of an aluminum alloy cylinder is 6 mm2. Composite cylinders are manufactured from either light weight steel or aluminum liners[1] and are encased within a high density polyethylene jacket or wrapped by carbon fiber, Kevlar, Twaron or glass fiber. These cylinders are ultra-light in weight, extremely durable and can be filled with high pressure of upto 4000 kPa.[1] They can hold 30% more gas than an aluminum cylinder of comparable size and 70% lighter in weight than steel cylinder. Composite cylinders are used by firefighters, paramedics, and emergency first responders.
The cylinder has a body, shoulder, and a neck. The curved upper part of the body is called as shoulder which tapers in a neck. The neck ends in a tapered screw thread into which the valve is fitted. When the valve is screwed to cylinder neck, a fusible material (Wood’s Metal) is used to seal leaks between the valve and the cylinder which melts if the cylinder is exposed to intense heat. This allows gas to release and lessens the risk of explosion.[1]
The valve is made of bronze or brass and is most fragile part of cylinder, therefore provided with a metal protection cap to protect [Figure 1]. It allows the cylinder to be turned on and off and provides a means by which the cylinders are filled and connected to yoke assembly on anesthesia machine or to regulator. The gas exits through the port. The valve contains a stem or shaft, which is rotated for opening or closing of cylinder. When the valve is opened the stem moves upward and gas flows to the port. During closure, the stem seals against the seat [Figure 2]. Two types of valves are in use. In the packed valve, the stem is sealed by resilient packing such as Teflon. In Diaphragm valve, a diaphragm separates upper and lower stem. Lower stem shuts or allows gas flow through the valve. The latter can be opened by only ½ or ¾ turns and is less likely to leak.[4]
