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 them.

However, the nature of the devices and vent systems depends on the type, size, location, regulations, and pressure of the hydrogen tank, storage tubes, or tube trailers and related system. There may be other means to protect against overpressure or fire exposure, and there are situations where the risk of a release could exceed the risk posed by the relief device and
vent system. For example, many GH2 transportation trailers in the EU are not equipped with PRD’s or TPRD’s which are not required by local regulations. Ultimately the decision and design of vent systems is based upon a hazard assessment.

Typical practice for gaseous tube trailers is to vent relief devices independently to the top of the vehicle. This is primarily to accommodate the large flowrates and high thrust forces involved from these releases. It’s fairly easy to do this since the vent lines are fairly short due to the maximum road height of trailers. Regulations do not prohibit piping multiple devices into a
single header and this manifolding is an acceptable practice provided that the design is done properly. It is important to design the header sufficiently large to be capable of handling the combined flow of the devices. These devices are primarily for fire protection and it’s likely that many, or even all, of the vessels would be exposed to fire at the same time.

It is common for LH2 transports to have all the relief devices/bleed valves connected to one vent stack.

Generally speaking, the International Fire Code and NFPA 2 apply to non-transportation use of hydrogen. These are maturing quickly, with NFPA 2 currently having issued its most recent edition in 2023. Standards for both on-board LH2 tanks and LH2 tankers for bulk fuel transport are managed by the U.S. Department of Transportation (DOT) and are well established. DOT transport requirements for the U.S. can be found in 49 CFR. 

There is growing activity regarding the use of LH2 as a vehicle fuel and there are several prototype trucks in operation. The on-board tanks may lack some reference standards, but vehicle fuel storage systems are typically self-certified by the original equipment manufacturers, particularly at the current state of development. While there is risk of impeding the development of a commercial market due to a lack of approved and common hardware, there is also risk of finalizing a standard prior to completion of development and testing. ISO TC 197 has several working groups including WG 1 and WG 35 to further develop the necessary standards for fuel tanks, fueling connections, and filling protocols. Liquid hydrogen transfer is well proven and established for industrial applications. However, consumer use of a cryogenic product has not yet been proven and will require refinement of hardware and processes.

The vehicle manufacturers can also provide guidance as to their efforts to meet required regulations.