The vent system should be designed for the temperature at which it operates (ambient for GH2 and Cryogenic for LH2). The outlet of the vent system should be designed for a fire to ensure the mechanical integrity of the vent system. 

The supports should also be designed for these temperatures and the associated expansion and contraction. 

It should be ensured that moisture…

Refer to the white paper completed by the HSP for LH2. The same criteria should be applied to
a vent system. See below.

H2Tools Document Library: White_Paper-Qualified_Individuals_for_Liquid_Hydrogen 

Similar qualifications for vent system design include:

1. A “qualified” individual for…

Design of vent header lines is critical to the safety of the system. From a process perspective, the pipe design must be sufficient to withstand back 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. Per ASME BPV Code requirements, backpressure should be limited to no more than 10% of the…

At NASA Cape Canaveral, they used a natural gas line connected to the vent stack outlet with a thermal sensor to make sure the pilot was lit. They may also have had a sensor to ensure the H2 fire was lit. In cases where substantial quantities of unused hydrogen is vented and the timing and amount of the flow rate is known and controlled, flaring might be useful. NASA guidelines stipulate that…

No, in nearly all cases, a deluge system is not needed. The proper sizing of relief devices using documents such as CGA S1.3 will ensure that they are of sufficient size to address worst case scenarios. In addition, if the system has been sited per separation distances from exposures in accordance with documents such as NFPA 2, then there should not be a significant risk of fire
exposure.…

There are no differences in the process design of the vent stack since the venting requirements will follow the same sizing and pressure rating requirements regardless of vent configuration. However, vent systems often create liquid air on their exterior due to the cold venting temperatures. Since this liquid air will drip off the stack, it should be diverted such that it does not directly…

Flame arrestors can be installed on hydrogen gas vents. The purpose of a flame arrestor is to prevent the migration of flame backwards and upstream into the vent stack or system itself. Generally, flame arrestors are not needed since: 1) the vent stack should be designed to withstand fire or explosion within the stack, and 2) the process generally does not contain a flammable mixture within it…

The main advantage of a “tee” style design is that the thrust loads at the vent exits are balanced. This means that an unequal force that might push the vent stack over is not present. Generally, the tee is also of the same size as the main vent line, thereby doubling the vent area for less pressure drop. The main disadvantage of a tee stack is that they generally vent with a horizontal…

The most common modes of failure for vent lines is backpressure and thrust forces.
Backpressure failures can be from several causes:

• Inadequate calculation of the backpressure caused by the high flow rates. Vent system design pressure is often only designed for the maximum 10% backpressure that is required by ASME Code. However, it should be noted that the large flowrates from…

Vent systems are typically open to the atmosphere, so it’s easy to overlook that they must be designed to withstand significant internal pressure. The two primary sources of pressure within vent systems are: 1) backpressure from the flowing gas, and 2) internal deflagration/detonation.

The large flows of gas exiting relief devices and vents will create backpressure within the vent system…