NFPA 409 Option 4 of 7.1 for Protection of Group II Hangars.
(4) A closed-head foam-water sprinkler system in accordance with Section 7.6.
7.6.1 Closed-head foam-water sprinkler systems shall be designed and installed in accordance with NFPA 16.
7.6.2 The minimum discharge density shall be 6.5 L/min.m2 (0.16 gpm/sq. ft.) of foam solution over the entire storage and service area.
188.8.131.52 Total Design Area
(A) The total design area shall be 5000 ft2 (465 m2)
(B) Where applicable occupancy standards specify design areas different from that specified in 184.108.40.206 (A), the occupancy standards shall take precedence.
A 220.127.116.11 (A) The design area can only be modified by occupancy standards, such as NFPA 409.
Now to my question: For a 20,000 sq. ft. hangar, I have concluded that the closed-head foam-water sprinkler system shall be designed for 6.5 L/min.m2 (0.16 gpm/sq. ft.) over the entire storage and service area or 20,000 sq. ft. (0.16 / 20,000) requiring >3000 GPM.
The sprinkler contractor is proposing a design of 0.17 gpm/sq. ft. / 5000 sq. ft. (flow required 1158.83 GPM / 45.312-psi), stating that
"although 7.6.2 above calls for 0.16 gpm/sq. ft. of foam solution over the entire storage and service area, this is only taken into consideration when determining foam requirements. We are required to ensure that the entire storage / service area is sufficiently covered with foam so the size of the area has to be taken into consideration."
Note: the water flow tests confirm 1151 GPM @ 5-psi with 74-psi static pressure.
Who has the correct interpretation?
a) sprinkler contractor (0.17 / 5000 with sufficient foam on hand to cover 20,000 @ 0.16) or
b) the writer (0.16 / 20,000)