Do you have experience/knowledge of putting heat/electrical tracing for vent stacks where freezing hazard is there?

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 stack fires.
• For liquid hydrogen system vents
  • Heat tracing is nearly useless for stopping freezing with a higher flow cold GH2 stream due to the amount of heat needed.
  • The vent stacks can develop liquid air, so the equipment must be robust to survive cryogenic conditions without damage.
• Maintenance on the heat trace equipment might require a system outage for personnel to work on it safely.