If you're using engines and/or turbines get a copy of NFPA 37 for starter. Figure out what you're local Gas Code Regulation is and follow that (overrules NFPA but is likely very similar). Around here, process and upstream oil and gas applications do not necessarily have to follow the local Gas Code as long as the designs are certified by a professional engineer and meet the intent of the codes (subject to a safety-codes officer's approval of course). That should get you started...