No, but it depends on the application. Nearly all vents less than 4” in size are not purged with N2. This is primarily due to: 1) large flows required to dilute hydrogen below the flammable range, 2) the cost of the nitrogen, 3) the potential blockage of the stack when being inserted a vent header/stack serving a liquid hydrogen system, 4) the potential for backpressure (depending on the…

There is no specific requirement not to vent liquid hydrogen from a vent system. Best practice would be to only vent gas from the top of the vessel to relieve pressure. If liquid must be vented, it should be vaporized first. 

Note: It is very unusual to have LH2 flow from a liquid tank out the vent system, as the vent system is connected to the vapor space on the LH2 tanks and there…

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…

I am not sure which picture you are referring to so I will attempt to answer.

If you are referring to the incident where a fire occurred and the vent system was damaged, then this may have been due to lack of proper supports and incomplete assembly of the test systems. In the past, vent systems were not pressure tested for strength but that is changing. 

If you are talking…

There is no standard which specifically specifies the use of a flapper. A properly designed flapper should provide de minimus restriction to vent flow, yet still provides weather protection which allows for a vertical release of the vent stack flow, which is best from a dispersion and radiation perspective. Flappers are extensively used successfully and safely on nearly all liquid hydrogen…

CGA G-5.5 states: All vent stacks shall be grounded and meet the requirements of NFPA 70, National Electrical Code, for integrity and system design and also references NFPA 77, Recommended Practice on Static Electricity, and NFPA 780, Standard for the Installation of Lightning Protection Systems. 

For lightening refer to NFPA 780 and for grounding of the Hydrogen equipment, refer to…

All vent stacks/systems should be bonded and grounded to minimize ignition sources. Higher pressure streams from higher velocities have a greater risk of igniting for several reasons, including particle impingement. Adding mesh could create more impact points for particulate, which would increase the potential for ignition, but would not increase the probability of a DDT. Similarly, high flow…

Liquid hydrogen is rarely vented as a liquid. If liquid hydrogen is vented, there should be a means to ensure that it is fully vaporized. The vent systems for LH2 tanks are connected to the vapor space on the tanks to ensure in most instances, this occurs. Most vents from a liquid hydrogen system will vent gaseous hydrogen, but this gas, may still be as cold as -420 F. There are no code…

It depends on the construction and location of the lights. Assuming the typical practice of using non-classified lighting on vehicles, operation of those lights during a delivery could provide an ignition source if located within the classified area near the delivery or venting activity. A more modern LED lighting systems may present a lower risk.

Because a small spark can ignite hydrogen-air mixtures, precautions such as using spark-resistant tools is one method that can be considered to reduce the probability of an ignition. However, there is little evidence that spark-resistant tools make a significant difference.   

Spark-resistant tools are made of nonferrous materials that are inherently weaker than the steels…