Previous versions of NFPA 55 listed overhead power lines within the separation distance tables with no voltage distinction. The separation distances were 15 ft for GH2 and 25 ft for LH2 for all overhead electrical lines. The current edition of NFPA 2 includes these in overhead utilities; the distance for GH2 and LH2 will vary with pressure and diameter of the hydrogen piping. In practice, high…

Each system should be evaluated for exposure of equipment to jet fires. The design team should develop
a plan to mitigate exposure as part of the hazard analysis. Fire barriers, walls, enclosures, and insulation
systems are frequently installed to meet code requirements where separation distances are not
sufficient or where the probability of exposure to a jet fire is high. Barriers…

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 lifetimes of these components will vary depending upon the application, their installation environment, and usage. It is also important to adhere to the component inspection, maintenance and replacement specifications as recommended by the manufacturer. However, as many are made of stainless steel, their life expectancy is longer than other materials. Estimated lifetimes are below in years…