Nearly all hydrogen storage tanks and hydrogen storage systems will need some type of pressure relief system to protect the vessels from overpressure. If there are pressure relief devices, some means to vent the hydrogen to a safe location will be needed. An exception to this is hydrogen cylinders due to their relief device type (lead-backed rupture discs (CG-4/5) and
the need to transport…

We are not certain what an inverted vent top is. If this means the hydrogen flow is pointed downward in any way towards grade, then yes it must be avoided. Less dangerous vent gases can be pointed downward, especially those that mix with air rapidly (nitrogen/oxygen/argon). Regardless, reaction forces must be taken into account for any relief valve activation or flow

There are many designs of storage systems where multiple vessels might be needed to obtain the required storage quantity. Regulations differ between vessels and modules which are intended for stationary or transportation purposes. Similarly, there are differences in codes globally. The issues of requiring shutoff valves on individual vessels and requiring TPRD’s are linked since generally…

Welded joints are always best, but they cannot always be used as a connection to tanks and tubes, as mechanical joints are needed for maintenance. Supports for the reaction forces can help ensure the mechanical joints in the piping does not pull apart. 

If large diameter or thick-walled tube is installed with compression fittings, the use of hydraulic swaging is recommended.

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Flame arrestors can be installed on hydrogen gas vents. The purpose of a flame arrestor is to prevent the migration of flame backwards and upstream into the vent stack or system itself. Generally, flame arrestors are not needed since: 1) the vent stack should be designed to withstand fire or explosion within the stack, and 2) the process generally does not contain a flammable mixture within it…

Hydrogen vent stack fires can create NOx. While not typical, certain municipalities will require air permits to address the emissions from hydrogen flare systems, and even from intermittent ignition of vent stacks. This is highly dependent on the location and interpretation of regulations. A hydrogen flare system is much more likely to require an air permit than a standard vent system.

There are many potential sources of delayed ignition. Hydrogen is easily ignited, and the larger the cloud, the more likely it is for it to find an ignition source. The cloud itself may serve as an ignition source as the force of the gas release may cause dust or other contaminants to mix in the air creating a static charge which ignites the hydrogen. Similarly, the force of the release can…

Heat tracing can be used as a safeguard against freezing. However, it must be understood that: 

• The heat trace system uses a utility supply so may not always be operational.
• The electrical equipment must be properly classified for the area, which can be challenging for the Div 1 classification for vent stack outlets.
• The heat tracing might be damaged by vent…

Yes, numerous incidents have occurred where frozen air (which contains oxygen) has built up within a hydrogen process or vent system. These incidents with vent systems incorporate more than just a vent stack, but include a vent system consisting of additional atmospheric equipment (such as a tank) where the equipment stays cold and allows air into the system in contact with a cold hydrogen…

The answer is dependent upon the nature of the system and a hazard assessment which evaluates a balance of risk. 

Keeping the hydrogen in the vessel is better so the hydrogen release does not compound the original hazard. Large flowrates from vessels can create significant risk of vapor cloud explosion, jet explosion, or radiation exposure. Vent systems can also fail from poor…