Heat tracing can be used as a safeguard against freezing. However, it must be understood that: 

• The heat trace system uses a utility supply so may not always be operational.
• The electrical equipment must be properly classified for the area, which can be challenging for the Div 1 classification for vent stack outlets.
• The heat tracing might be damaged by vent…

Yes, numerous incidents have occurred where frozen air (which contains oxygen) has built up within a hydrogen process or vent system. These incidents with vent systems incorporate more than just a vent stack, but include a vent system consisting of additional atmospheric equipment (such as a tank) where the equipment stays cold and allows air into the system in contact with a cold hydrogen…

Vent stacks must be designed for a fire at the outlet. The mesh is designed to ensure no blockage of the vent stack by animals/insects. 

Additionally, the mesh must be designed for pressure drop to ensure code-compliant back pressure on the relief devices.

Rupture discs open very rapidly. Historically, rupture discs opening at high pressure (1000 psig and above) have caused the most damage due to deflagration/detonation. Timing a rupture disc would not be possible. Additionally, how would you have a pilot light on a moving tube trailer? Even with a pilot light at the end of the stack may blow out due to the initial high velocity.

See…

In laboratories, 316 stainless steel tubing is frequently the first choice for small flow and pressures less than 2800 psi (19 MPa). See Best Practices: Material Compatibility for hydrogen compatibility with various materials. Always work within manufacturer’s pressure ratings adjusted for temperature. Read and follow…

There are several resources that can help review designs, such as the Hydrogen Safety Panel and other outside consultants that are members of the Center for Hydrogen Safety.

See H2Tools, Best Practices: Purging, for a description of different purging approaches for hydrogen systems.

Electrolyzers should be installed per manufacturer recommendations and meet the criteria of their
listing, such as ISO 22734, Hydrogen generators using water electrolysis - Industrial, commercial, and
residential applications. There are several methods such as partitions, enclosures, ventilation, and
purging that can be used to address non-classified electrical equipment.

There are dozens of safety considerations for safe design of hydrogen vent stacks. Their primary function
is to vent the hydrogen safely, so vent stacks should be designed such that the gas dispersion and
radiation profile (if ignited) do not impact surrounding equipment, buildings, or people. Documents such
as CGA G5.5, Hydrogen Vent Systems, provide numerous details regarding design…

As with any high pressure gas, hydrogen vents can be very loud. Consideration must be given to the
surrounding population and special provisions can be taken to reduce the noise level of releases if
needed. When installed, care must be taken that the sound quieting system can withstand the
flow/pressure of the release and does not impede the required flow.