Because hydrogen leaks frequently ignite, and because about half the time the ignition source is not identified, when evaluating hazards with hydrogen leaks, many people just assume the leak will be ignited. Note that consideration needs to be made for what may happen with immediate ignition (jet fire) and what may happen with delayed ignition (explosion). 

It is still important to…

Sprinkler systems and other fire suppression means are prescribed per building and fire codes to limit fire spread to other materials. In the case of a hydrogen leak and fire, it is best practice to isolate the hydrogen source, and let any residual hydrogen gas burn out. Even if the initial fire is extinguished, additional leaking hydrogen may accumulate and ignite with the potential for an…

Outside storage is generally considered safer and is required for large amounts of gas. Stationary storage should be located outside at a safe distance from structures and ventilation intakes, and protected from vehicle impact. 

Hydrogen storage separation distance requirements are typically based on the quantity and pressure of the hydrogen or the piping diameter, depending on the…

The answer is dependent upon the nature of the system and a hazard assessment which evaluates a balance of risk. 

Keeping the hydrogen in the vessel is better so the hydrogen release does not compound the original hazard. Large flowrates from vessels can create significant risk of vapor cloud explosion, jet explosion, or radiation exposure. Vent systems can also fail from poor…

There are many potential sources of delayed ignition. Hydrogen is easily ignited, and the larger the cloud, the more likely it is for it to find an ignition source. The cloud itself may serve as an ignition source as the force of the gas release may cause dust or other contaminants to mix in the air creating a static charge which ignites the hydrogen. Similarly, the force of the release can…

Absolutely. Vent systems will experience a variety of transient conditions of pressure, temperature, and thrust load, so stress analysis to anticipate the strength and flexibility needed are important for safe design. These issues are often overlooked and only become an issue when they are called upon to operate in emergencies. 

It is a best practice to include the vent system in…

Delayed ignition is a significant hazard for hydrogen releases, either intended or unintended. The primary concern is the overpressure and energy release created from a vapor cloud which could contain a significant quantity of hydrogen. The H2Tools Incidents database contains a number of examples of delayed ignition. 

Water icing at the exit of a stack is certainly an issue in cold climates. Significant effort has been put into vent stack outlet design to minimize the probability. Documents such as CGA G5.5 have topworks that are recommended. Stacks that face upward have a higher probability of having water, ice, or snow enter the stack and freeze. 

Several programs can predict this such as HyRAM or PHAST. The inputs are critical to a safe
answer.

This is not a simple answer due to the many types of flame lengths and flame orientations due to pressure and direction. NFPA 2 recommends that vent systems should be designed so that if the safety relief valve is relieving at capacity the radiative heat felt by an individual at grade…

AICHE ELA253 CHS ” Introduction to Hydrogen Safety for First Responders” is a good reference and discusses both LH2 and GH2. LH2 fires are very unusual. LH2 releases usually are GH2 so the fires at either ambient for low flow or the GH2 is a cryo temperature for high flow. Fires from LH2 tanks ignite less frequently than GH2 high-velocity releases. The colder the gas the less potential for…