You could look at the expanded commentary in the NFPA 72 Handbook. That will give you more information on the "why's" of the code. Not cheap; about $250 if you aren't a member of NFPA. Member discounted price is $219. Membership is $225 and you get full on-line access to all the NFPA codes. See if your company will spring for it.
Another resource some people like is the National Training Center's (NTC) Brown Book, Fire Alarm Systems Handbook. Don't let the word "National" fool you; it's a commercial operation.
Between these two, you should have a very good background for fire alarm system design. Even more useful is to take system specific training. The big guys (Honeywell, Siemens, Simplex) offer various opportunities for you to get more information/training on their products, especially for engineers and architects.