The requirement for relief valves shall be assessed on a line by line basis to meet code and project requirements. In hazardous vapour services, the relief valve seat shall be protected from the process through a bursting disc or water seal. The water seal shall have provision for making up any water loss and shall have a drain valve piped to the drain system. When utilising a burst disc, a tell-tale pressure gauge shall be installed between the burst disc and the relief valve.