Pressurized vessels or boilers shall be provided with overpressure protection by means of a listed pressure relief valve installed in accordance with the manufacturer's installation instructions.
The discharge piping serving a temperature relief valve, pressure relief valve, or combination of both shall have no valves, obstructions, or means of isolation and provided with the following:
- Equal to the size of the valve outlet and shall discharge full size to the flood level of the area receiving the discharge and pointing down.
- Materials shall be rated at not less than the operating temperature of the system and approved for such use.
- Discharge pipe shall discharge independently by gravity through an air gap into the drainage system or outside of the building with the end of the pipe not exceeding 2 feet (610 mm) and not less than 6 inches (152 mm) above the ground and pointing downwards.
- Discharge in such a manner that does not cause personal injury or structural damage.
- No part of such discharge pipe shall be trapped or subject to freezing.
- The terminal end of the pipe shall not be threaded.
- Discharge from a relief valve into a water heater pan shall be prohibited.
Where the operating temperature exceeds 212°F (100°C), the discharge pipe shall be installed with a splash shield or centrifugal separator.
Where the discharge from safety valves is capable of being hazardous, discharge of steam inside the boiler room, such discharge shall be discharged to the outside of the boiler room. Discharges from relief valves on industrial boilers shall be discharged to an approved location.
Hot-water heating systems that are subjected to a vacuum while in operation or during shutdown shall be protected with a vacuum relief valve. Where the piping configuration, equipment location, and valve outlets are located below the boiler elevation the system shall be equipped with a vacuum relief valve at the highest point.