Purging of vent systems is not required and in most instances is not recommended.

A nitrogen purge is generally not needed for a vent system designed in accordance with CGA G-5.5.  However, there are times where this might be considered or required due to the specific design of a system.  Where determined by a risk review to be needed, A continuous purge into a vent system…

Off gassing of hydrogen from battery sources depends on battery chemistry, usage/duty cycle, age, and other considerations. The specific battery manufacturer should provide recommendations for fire prevention and mitigation in battery charging rooms as the battery itself impacts how an event would be mitigated. Adequate ventilation such that combustible mixtures cannot develop is a general…

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, the pressure safety relief system on LH2 tanks is sized for the loss of vacuum condition. The spring-loaded safety valves are sized for lower demand cases such as runaway pressure build or loss of vacuum. Higher demand requirements, such as loss of vacuum combined with fire, are handled by the rupture discs and are sized for such an event.

The cleanliness of an H2 piping system is often based on end use requirements since the purity of the system may impact the end use application. Cleanliness required for end use purity is usually much greater than that required to prevent condensation or oxygen content sufficient to create a safety risk. While not required for the same safety reasons as oxygen safety, specifying a system to be…

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…

There is no generalized exception for hydrogen fueling stations.  However, PSM is intended for employee protection. It’s not intended for retail operations or customers. Through paragraph 1910.119 (a)(2)(1) of the regulation, PSM exempts retail facilities. Some may use this exemption as a means to exclude H2 retail fuel sites from PSM.

Fuel stations that are non-retail, such as…

The information provided is not only outdated in terminology, but also misleading in quantifying the dispersion of hydrogen in terms of comparison of diffusion of air in air. Hydrogen diffuses 4X faster than air, and the rate of mixing has many variables, so there isn’t just one answer. However, it’s generically safe to say that an initial hydrogen gas cloud outdoors and unconfined will…