In almost any laboratory or research and scientific facility, there are numerous devices, instruments, or processes that require gases to run the instrumentation or process or to calibrate the devices. Gas cylinders that are located in the laboratory area can present significant hazards, and the space they take up can be better used for other more appropriate purposes. Gas delivery systems that are properly designed, sized, and located can improve safety in the laboratory. In addition, attention to high-purity requirements—purity, compatibility, flow, materials of construction, and more—is vital for safety, performance, and cost-efficiency.
There are a number of codes and standards that apply to the storage, use, and installation of gases and their delivery systems.
The first step in properly designing any gas installation, whether it is for a new facility or a retrofit, is to conduct an audit or survey of the gases required for each location or laboratory. Identifying what gases are required for each instrument, their purity level, required delivery pressure, and peak flow demand is essential in determining everything from the size of the piping required, to the storage area required, and even the mode or source in which the gas may be supplied. Overestimating the pressure or flow requirements can result in higher installation costs and reduced gas savings resulting from residual contents left in cylinders or higher monthly rental fees on cylinders that are not required. Underestimating, however, can cause inefficient supply of gas to critical instruments or systems that impair their use or operation.
There are some very specific storage and separation requirements for the areas in which compressed or cryogenic gases are stored and/or connected to a building’s gas delivery system. As a minimum, gas cylinders should be stored and secured in an upright position using brackets, chains, or straps in a well-lit and ventilated area away from combustible materials and sources of heat or ignition.
When determining what size pipe or tubing to use for a specific application, the main consideration is to determine what the maximum required flow for that specific gas would be if all application or use points were flowing to their maximum at the same time. This can be found by totalling the individual use points and applying a conservative safety factor to allow for growth of requirements of at least 20–50%, depending on what the future outlook is for that gas
For almost all laboratory gases, maintaining gas purity is a critical requirement. To that end, the choice of materials of construction and their compatibility with that specific gas and its purity level must be considered. It is not enough that the materials are compatible with the specific gas, but that the design ensures and retains the purity of the gas. From the inlet to the outlet, a system that is designed with either bar stock brass or 316L stainless steel components is desired over forged components. Any diaphragms should be made of 316L stainless steel, and the diaphragm seals should be of a metal-to-metal design.
Though there are many other areas that must be considered, the primary areas of concern are where to locate the gas storage area outside the laboratory, how much gas will be required, and how the gas will be delivered to the end use points. Users who follow these guidelines are well on their way to selecting a safe and cost-effective gas delivery system.