Many organizations are involved with the specifications of safety and pressure relief valve design, performance or application. Some of the most common organizations have web pages and are listed here ASME The American Society of Mechanical Engineers - This site also has a link to the publication Mechanical Engineer. NBBI The National Board of Boiler and Pressure Vessel Inspectors - Organized in 1919, the NBBI plays a major role in the preservation of public safety in their role as the ASME's designee.
Site includes a searchable database.
API American Petroleum Institute - Api's involvement in publishing specifications for safety and pressure relief valves is well known in refining and processing industries. NACE National Association of Corrosion Engineers - NACE is most well known for their metalurgical specifications for materials offering resistance to corrosive service fluids. ANSI American National Standards Institute - There are not many manufactured products that do not have one or more components that comply with ANSI specifications. ISA Instrumentation Society of America - Members of ISA are probably more involved with the selection of pressure and safety relief valves in system design than any other group. An interesting site.