IEC 60079 part 10 or EN 60079-10 if you're somewhere other than North America.
Oil & gas industry, perhaps the Energy Institute's EI 15 (formerly IP 15) code of practice.
If the issue is HazLoc, I am not sure NEC 500 would apply for TEG as:
Group A. Atmospheres containing acetylene
Group B. Atmospheres containing acrolein, butadiene, ethylene oxide, propylene oxide, hydrogen, or fuel and combustible process gases containing more than 30% hydrogen by volume
Group C. Atmospheres containing ethyl ether, ethylene, or gases or vapors of equivalent hazard
Group D. Atmospheres containing acetone, ammonia, benzene, butane, cyclopropane, ethanol, gasoline, hexane, methane, methanol, naphtha, propane, or gases or vapors of equivalent hazard.
Whereas Class II (Groups E,F,G) are the dusts, etc.
The application also matters - for instance, if the application is for a fixed or floating platform, say petro, etc) than API
s RPF or RPF/Z 500 would apply - however, virtually identical to NFPA 500. You may want to start with the MSDS - which shows TEG to be the F1 hazard to be pretty low, or must be preheated before ignition can occur. If in the US, the HMT in 49 CFR would apply, but mostly speaks to packing and shipping.
