Most common odorants will contaminate fuel cells. Additionally, hydrogen's small molecule and high buoyancy make it challenging to find a compatible odorant. Research is being conducted on fuel cell compatible odorants, but there are none currently in use. Like liquefied natural gas, liquid hydrogen also can’t be odorized due to its cryogenic temperature.

Hydrogen flames can be nearly invisible in daylight, especially at low flowrates. The concentration of hydrogen does not have much effect on the color of the flame. Many hydrogen incidents or fires will have a bright orange hue, or even yellow flames. The color is primarily caused by contaminants that is either naturally in the air in certain environments, swept into the air during the release…

Yes, small flowrate vents may be invisible, particularly in daylight. Sometimes it may still be possible to see heat striations in the air from the heat generated by the fire, but it can be difficult to discern at low flowrates. 

Several organizations published a paper together on this topic in 2017 (see attached). Based on comparisons with tests and CFD simulations, the following conclusions were drawn:

1. The gas concentration for vapor cloud explosion blast load calculations for H2 jets can be limited to approximately 10% to 75%. Note that testing for H2-air VCEs in congested environments has been performed…

The “Hydrogen Ready Appliances Assessment Report” published by the Northwest Energy Efficiency Alliance (NEEA) in February, 2023, is one of the most recent studies on this topic.  Several key items from the report pertaining to this question include the following:

1.    “There appears to be growing consensus that blends of up to 20% or perhaps even 30% are…

1.    As of January 2024, we are not aware of any public data on incidents or investigations where a hydrogen fired steam boiler exploded.

2.    The potential for detonations within a boiler tube would depend on both the equivalence ratio of the hydrogen present and the diameter of the boiler tube.
a.    At a minimum, if the circumference of the tube is…

A design condition for vent stacks is to always assume that the hydrogen will ignite. The stack musts be designed such that it can withstand those conditions as well as minimize radiation to surrounding personnel and exposures. Although hydrogen fires have comparatively low radiation compared to hydrocarbon fuels, the radiation from large releases from vent stacks can be quite high. Documents…

The purity required will be a function of the end use application. There are a variety of grades of hydrogen that can be purchased. The H2 purity will also vary based on source (GH2 or LH2) and production method. CGA G-5.3, Commodity Specification for Hydrogen, lists several typical purities of both liquid and gaseous hydrogen. Standard GH2 available from most suppliers is 99.95% hydrogen.…

Yes, although not as common as high-pressure gas releases, high-velocity cold H2 gas has ignited during rupture disc and relief valve activation.

The water vapor cloud formed from venting cold hydrogen gas from a liquid hydrogen tank will vary in size depending upon atmospheric conditions including ambient temperature and humidity. There is not a direct relationship between the water vapor cloud and the flammable cloud of hydrogen, but it’s often used as a proxy. 

Initially upon release, it is possible that H2 vapor from…