The volumes and types of compressed gases used as chemical precursors, catalytic reagents and process materials continue to grow. Some of these gases are toxic, corrosive and reactive in the chemical processing environment and so clearly pose hazards. However, even benign inert gases can be a challenge if they aren’t handled properly.
From large petrochemical units to tiny pharmaceutical pilot plants, day-to-day operations depend upon providing these gases in a controlled, safe and environmentally conscious manner. Safe delivery requires strict adherence to a plethora of formal codes and specifications. Failure to achieve safe operation isn’t an option.
Planning begins with understanding that all compressed or cryogenic gases are considered hazardous materials and must be given the respect and importance that implies. Fire, health and safety, as well as environmental codes dictate the need to store, use and contain hazardous materials in a safe and effective manner. The cost for failing to comply makes it imperative to use the best available technology, material and procedures for pressure and flow control systems. Materials and systems selected must be compatible not just with the specific gas being used, but also with the environment to which they are subjected and the pressure and flow the process entails.
At the practical level, safety involves the following procedures, which also can improve efficiency:
- locking out equipment;
- matching gas handling hardware to the process gases being used; and
- managing delivery of raw materials into processes with high-quality pressure and flow control equipment.
Venting is the discharge or release of a gas from a contained system or device. Any venting or release of hazardous gases, whether intentional, e.g., as part of a cylinder change, or as the result of system or component failure, must be contained and properly handled. In many cases uncontrolled release of toxic or acutely hazardous gases in even small amounts poses safety hazards and the possibility of hefty fines. It, therefore, is imperative to assess potential sources or conditions that could cause venting from the gas delivery system. You must arrange for control, containment, and in the case of toxic or acutely hazardous gases, delivery to appropriate disposal, scrubbing or abatement systems.
Always keep in mind that all compressed or cryogenic gases are considered hazardous materials. Toxic and acutely hazardous gases obviously demand rigorous oversight and scrutiny. But don’t forget the risks posed by the uncontrolled release of inert gases such as nitrogen, argon and carbon dioxide — in confined spaces, these gases can present asphyxiation hazards that must be appropriately addressed. Venting from the cylinder, container, cylinder connection, pressure regulator or control devices, pressure relief device and pipeline are areas of concern that should be evaluated. Then, implement systems or procedures to preclude hazardous outcomes.
From a procedural standpoint, it’s essential to have a receipt and inspection procedure in place for all compressed gas containers delivered onsite. For toxic or acutely hazardous gases, using portable leak-detection equipment and training receiving personnel is the best method to ensure that leaking cylinders or containers aren’t taken into inventory.
Dealing with leaks from containers already onsite depends upon the specific gas and whether a pressure or safety relief device is located on the cylinder or as part of the cylinder valve. In the case of most extremely toxic gases, there’s no pressure or safety relief device on the container or cylinder valve. Where relief devices are part of the cylinder or container, they may be burst-disk safeties in the case of inert or less hazardous gases, or fusible plugs that only release contents when exposed to extreme heat, as with many flammable gases like hydrogen.
Storage location or enclosures are the only methods of containing product venting as a result of failure of the cylinder valve or safety relief device. National and local fire, health and safety codes specify what can be stored where and standoffs, minimum allowable distances from emergency exits, electrical hazards and ventilation systems. In general, toxic and acutely hazardous gases must be stored in designated areas with containment means such that a release of cylinder contents can be safely vented to abatement systems or scrubbers.
Address venting from cylinder connections, pressure regulators, pressure relief devices and pipeline sources by selecting appropriate equipment and systems that deal with these sources and allow for system purging. The primary sources of leaks from pressure regulators are connections, diaphragm seals, or in the case of diaphragm failure, through the regulator bonnet. So, select a regulator or pressure control device that comes as complete as possible, including gauges, valves or accessory options, with a Helium leak certification of at least 1 × 10-8 cc/sec from the manufacturer. Figure 1 shows one example, a regulator with a Type 316L stainless steel diaphragm, a pipe-away captive vent kit and pipe-away pressure relief device.
It’s important to note that the pressure relief devices included on pressure regulators aren’t designed to protect downstream pipelines, equipment or processes, but only regulator components or assemblies. To protect pipelines from rupture or venting, use separate dedicated pressure-relief devices that are preset and capable of piping any emissions to appropriate abatement systems or areas of release.