Use of gas cylinders

A large number of gases are commercially available and details about individual gases are provided in Sections 7.5 and 7.6. The purpose of this section is to describe safe methods for handling the containers in which these gases are supplied. 

Handbook of Cornpressed Gases, Compressed Gas Association, Reinhold, 1981. 

For this reason cylinders and lecture bottles should never be allowed to stand unsupported. 

They should always be securely clamped to a bench or a wall. If they have to be moved frequently they should be supported in a sturdy metal frame, or in a trolley designed for this purpose. Cylinders should only be moved in purpose designed trolleys and should always be treated with great care. 

Cylinders are generally pressurized to 175-200atm and the on/off valves provide no more control than their name suggests so cylinders must be fitted with a regulator to allow controlled delivery of the gas. The most popular regulators are the two stage types shown in Fig. 7.2. 

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The information regarding how the FARCs had access to CW primitive technology refers to the IRA [9]. Several press reports mentioned that groups of IRA s members made trips to Colombia with the objective of training FARCs troops, first in the use of gas cylinders and later in the use of cyanide in bombs or how to ammunition it in bullets. 

The most common problem associated with the use of gas cylinders is the problem of leaks. The cylinder can develop leaks at any of four points, assuming that no gross rupture of the cylinder wall itself has occurred the valve threads, valve safety device threads, the valve stem, and the valve outlet. Repairs of leaks in the first two of these would require repairs done at high pressure and are not to be attempted in most laboratory facilities. It may be possible that some adjustments are incorporated into the design of the cylinder to allow stopping leaks in the latter two areas. In either case, it is best to contact the manufacturer for advice before attempting any repair. Forced freeing of a frozen or corroded valve should not be attempted. 

Learn the correct use of gas cylinders. Even a small gas cylinder can become a lethal bomb if not properly used. 

A list of guidelines, derived from various sources, to the safe handling and use of gas cylinders follows. A two-part series [32] expands on these rules and discusses certain special conditions. Most of the precautions listed below are paraphrased from rules established by tiie Compressed Gas Association. Some also appear in DOT regulations. 

We will mention only briefly here the fact that although most spills are thought of as being either liquids or solids, there is also the possibility of a gas leak from a cylinder or perhaps a methane leak from natural gas lines in laboratories. These can obviously be very dangerous with regard to toxicity or fires and explosions. Use of gas cylinders in introductory labs is uncommon, however. 

HSG 168 Fire safety in construction work HSE Guidance leaflet INDG 308 Safe use of gas cylinders... 

Common controls. All workers handling or using cylinders must have basic training in the use of gas cylinders, emergency shutoffs, proper equipment design, leak-testing procedures, and the use of appropriate respiratory protection in the event of a release of a compressed gas. Other controls include the following ... 

A fuel gas under pressure which may be hydrogen, towns gas, acetylene or propane. With special nozzles, low-pressure acetylene or butane can be used, but it is not common practice. The use of single cylinders of fuel gas is now giving way (except under site conditions) to the gases drawn from bulk liquid storage. All modern installations use flowmeters in the gaseous feeds. 

Seamless steel pressure vessels are the most common method in use today for hydrogen transportation at short distances (<200 km) and when small quantities are involved (up to about 500 kg). The different vessel options include cylinders, manifolded cylinder pallets and tube trailers. While single cylinders or manifolded pallets are trucked to the destination and off loaded, tube trailers, which consist of several steel cylinders mounted to a protective framework, are often left in place and replaced when empty. Transporting hydrogen in liquefied form is seven times more efficient in terms of actual hydrogen weight transported than using compressed gas cylinders. 

The sources of acetylene, nitrous oxide, and sometimes air are usually steel cylinders of the compressed gases purchased from specialty gas or welders gas suppliers. Thus, several compressed gas cylinders are usually found next to atomic absorption instrumentation and the analyst becomes involved in replacing empty cylinders with full ones periodically. Safety issues relating to storage, transportation, and use of these cylinders will be addressed in Section 9.3.7. The acetylene required for atomic absorption is a purer grade of acetylene than that which welders use. 

Bourdon gauges are used on gas cylinders and are also considered a type of aneroid gauge. These devices have a coiled tube (shown in Figure 3.5) and are used to measure the pressure difference between the pressure exerted by the gas in a cylinder and the atmospheric pressure. The coiled tube is mechanically coupled to a pointer (shown in red). As a gas at a pressure above atmospheric pressure enters the coiled tube, it causes it to slightly uncoil, kind of like those New Year s Eve paper noisemakers. This causes the pointer to move over a numerical scale, thereby indicating the gauge pressure in the tank. 

If a catalyst in a form of solid cylinders is replaced by hollow cylinders with an optimal internal radius, the reactor productivity will increase although the total mass of catalyst decreases. For example, the use of hollow cylinders with an internal radius of 035RU instead of solid cylinders of the same external size for the water-gas shift reaction at a pressure of 3 MPA and a temperature of 417 °C may increase the effectiveness of the unit reactor volume by 18%. This is particularly important for processes under elevated pressures, because of the strong dependence of the reactor cost on its volume [17]. 

Having decided on the number of gas cylinders required these should be positioned in the laboratory so that semi-permanent PVC (Tygon) tubing lines can easily be taken to each bench and to each piece of apparatus requiring a supply. Some of the apparatus commonly used in conjunction with inert gases will be described below and in Chapters 7 and 9. 

As soon as a larger number of different gas mixtures is necessary (either because characteristic curves of analyzers are to be taken at several concentration points, or because a wide variety of analyzers with different gas compositions in differing concentration ranges are to be calibrated), a large number of gas mixture cylinders must be kept on stock. As gas mixtures are expensive, and a large number of gas cylinders must be stored and handled, it is worthwhile to use multi-functional calibration gas generators. 

Colours play an essential safety role in giving information for use in tbe prevention of accidents, for warning of health hazards, to identify contents of gas cylinders, pipeline and services, the identification and safe use of cables and components in electronic and electrical installations as well as the correct use of fire-fighting equipment. 

Note that gas jars of oxygen can be produced using a gas cylinder or an oxygen generator. 

Write a short essay on the construction, use, and care of gas cylinders. 

Leave valve protection caps in place and hand-tightened until cylinders are secured and in use (or connected for use). Some types of gas cylinders have valve outlet caps and plugs that form a gas-tight seal. Keep the device on the valve except when containers are secured and connected. 

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