Liquid hydrogen is much less likely to pool than liquified natural gas (LNG) due to its low heat of vaporization. Very large facilities are often equipped with methods to enhance vaporization, such as crushed stone under tanks, as well as diversion systems to allow liquid hydrogen to spill and boil off in a safe area. Care needs to be taken that diversion systems do not create a hazardous…

Codes and standards to address issues like this one are under development, along with applied research and field trials. As with any new application, appropriate codes and standards must be developed to meet public risk targets.

The design of vent systems is critical to the safety of the system. From a process perspective, the pipe design must be sufficient to withstand back pressure, internal pipeline pressure, deflagration pressure, thrust forces from the flow, and must be of a sufficient size to not create a restriction that prevents proper flow or activation of the devices. 

The vent system…

It is best to avoid planned blowdown of large amounts of hydrogen inventory at high flowrates if possible.  Low flow releases from vent systems are normal and occur for purging, delivery operations, and maintenance activity.   A challenge with high flow blowdown of a hydrogen system is that venting large quantities of hydrogen can itself be a hazardous activity.   …

Welded systems are generally preferred, where possible, to reduce the likelihood of leaks.  Generally, even welded systems will need non-welded joints (e.g. unions, flanges, etc.) to allow maintenance replacement of components.  A low-pressure system would not be an exception to this preference.  However, piping at lower pressures and smaller sizes will…

There are several concerns with “snuffing” a hydrogen fire from a vent stack. Most importantly, snuffing a hydrogen fire before the hydrogen is isolated can lead to the buildup of a hydrogen vapor cloud, which may then re-ignite, especially with hot surfaces available from the previous fire. The largest hazard is an explosion of the vapor cloud…

TIA 1783 points out a valid concern about how to address the electrical classification zone around a liquid hydrogen system. The existing requirements specify 3' around the outlet of the stack for Division 1 and 25' around the outlet of the stack for Division 2 area. These distances are historical and date back to the 1960's. They are a "one size fits all" simple approach that is easy to…

The primary safety standards for applicable to this piping in the U.S. are ASME B31.3, B31.12, and NFPA 2. The editions used should be those adopted by the local jurisdiction. Design of an LH2 piping system should always be conducted and reviewed by engineers experienced in cryogenic piping design. The equipment should also be installed per NFPA 2 and NFPA 55. IT is recommended that the piping…