1) Please don't write all in capitals next time. It means you're SHOUTING!!!
2) Fire water systems can be very odd. You need to look at NFPA codes normally. I think they don't like pressure relief valves because they can fail and let water out when they shouldn't.
You can get small thermal relief valves allowed, but not full flow ones AFAIK. And any item needs to be "approved".
Take great care with FW systems
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.