Gas Reticulation Systems for Safety, Performance, and Cost-Efficiency in the Laboratory
In almost any laboratory, research or scientific facilities, there are numerous devices, instruments and processes that require gases to run or to be calibrated. 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. This article is not meant to detail them all, but will reference portions of those standards and codes as they apply to the general principles of gas storage and delivery systems.
The South African codes and standards that are most significant for Laboratories are:
- Occupational Health and Safety Act (No. 85 of 1993)
- Pressure Equipment Regulations No. 734 (Government Gazette 32395 published on 15th July 2009)
- SANS 827 The installation of pipes and appliances
- ASME B31Q Standard of Pressure Piping
- EN13774 Valves for gas distribution systems with maximum operating pressure less than or equal to 16 bar – Performance requirements
Laboratories must understand and follow these codes and standards thoroughly in order to comply with the minimum requirements of any gas system.
The LGA 4 Step Gas Installation Process
1. Gas requirement audit
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.
2. Selecting a location for storage and gas delivery systems
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. They may vary by local code requirements, but at a minimum must meet tho OHS standards. 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. The gases should be separated by hazard type. Space should be allowed to segregate full from empty cylinders with the appropriate hazard notification signage as required.
3. Pipe sizing and flow considerations
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 totaling 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.
4. Choosing the right gas delivery system
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.