ASME I Part PTFH need PSV

[gigaspan]

I'm involved in the construction of a Liquid Phase Thermal Fluid Heater in accordance to ASME I Part PTFH.
Considering that the heater and system are open to atmosphere, it's required to install a pressure relief valve?

 

[georgeverghese]

Why open to the atmosphere? I dont know of any thermal heat transfer fluid that doesnt oxidise / degrade at high temp when in contact with air. Heat transfer fluids are all operated in closed recirculation loop.