There are several codes and standards that call for the use of Hydrostatic Relief Valves (HRV) and often times the implementing organization fails to meet these requirements fully. As for propane systems, both OSHA and NFPA, require the installation of HRVs EVERYWHERE there is a chance that liquid propane can be trapped, but as this Nevada LP Gas Board Inspector states, many find excuse after excuse not to install these HRVs. Here is his story and a VERY GOOD scenario that many never consider when justifying these valves are not needed. Although a particular valve has “never been closed” does not mean it can not be closed!
1910.109 – Storage and handling of liquefied petroleum gases has the following requirement for Hydrostatic Relief Valves (HRV)…
1910.110(b)(10)(xii) A hydrostatic relief valve shall be installed between each pair of shut-off valves on liquefied petroleum gas liquid piping so as to relieve into a safe atmosphere. The start-to-discharge pressure setting of such relief valves shall not be in excess of 500 p.s.i.g. The minimum setting on relief valves installed in piping connected to other than DOT containers shall not be lower than 140 percent of the container relief valve setting and in piping connected to DOT containers not lower than 400 p.s.i.g. The start-to-discharge pressure setting of such a relief valve, if installed on the discharge side of a pump, shall be greater than the maximum pressure permitted by the recirculation device in the system.
This is about as straight forward as we can ask for from OSHA and yet we find some of the wildest excuses for not installing HRVs where required. As this Inspector from the Nevada LP Gas Board points out, just because a manual valve has never been closed in “X number of years” does not mean it will never be closed. Take into consideration an emergency responder closing a manual valve to shut-off the flow of LPG to a fire in order to snuff out the fire. They are doing what they have been trained to do, under the assumption that the propane system is designed properly! CLICK HERE (pdf) for his article.
PLEASE NOTE: although this article is specific to propane, there are other codes for volatile liquids that have very similar requirements.