Building Gas Flow Restrictions

[JLSeagull]

In the hydrocarbon processing industry we normally package online analyzers in an environmentally controlled non occupied building. Typically we apply flow restrictions for the carrier gas etc. entering the analyzer shelters. These restrictions can be set to limit the flow but the criteria for setting the limit does not appear to be clearly established. I am looking for applicable codes or standards for the flow restriction settings. The objective of the restriction is to stop excess flow in the event of a tubing rupture. We normally have gas detectors for oxygen deficiency, hydrocarbons, perhaps hydrogen, etc. The HVAC is normally set for six air changes per hour and much greater air flow upon detection of combustible gas or other detected gas within the building. Usually the HVAC rates are selected to assure adequate ventilation associated with electrical area classification issues. One criterion found pertains to HVAC "dilution capability of the protective system" per the NFPA 496 Appendix A, with non mandatory background that is not part of the standard. What other code, standard or common criteria applies to flow limiting devices for analyzer shelters or similar non occupied buildings?