First the NFPA 96 is a guide and NOT the code. You will need to check your local jurisdiction whether fire sprinkler in grease ducts are required.
Taken from NFPA 13, 2007 ed. 7.10.3.4.1 Where ducts do not exceed 75 ft (22.86 m) in length and the entire exhaust duct is protected in accordance with UL 300, Standard for Safety Fire Testing of Fire Extinguishing Systems for Protection of Restaurant Cooking Areas, sprinkler(s) [or automatic spray nozzle(s)] shall not be required.
In all the high-rise grease exhaust projects I worked on, aprinklers were ALWAYS used in the grease duct.
I was told be the local fire marshal that if my project was for a 1 story building than NO spinklers would be required. I have yet to design for a 1 story building.
Check with your local jurisdiction to see if sprinklers are required. If the building dept. cannot assist you, go check with the fire dept.
----
A green thought..."We don't inherit the earth from our ancestors, we borrow it from our children." (unknown)