I am working on a sprinkler system design for cable tunnels in a power plant. I am referring to NFPA 13, and found the below clause which is a little bit confusing:
22.214.171.124.1 Automatic sprinkler systems shall be designed for a density of 0.30 gpm/ft2 (12.2 mm/min) for the most remote 100 linear ft (30 m) of cable tunnel up to the most remote 2500 ft2 (230 m2). [804:10.4.2.2.2]
What makes me confusing is the part in bold. Let's say there is a cable tunnel whose width is 10 ft and length is 300 ft. In this case the area of cable tunnel for the most remote 100 linear ft is 1000 ft2. Should I extend the area further to 250 linear ft so that the area become 2500 ft2 for the design of the sprinkler system? Or I can only consider the 100 linear ft of cable tunnel even though the area is less than 2500 ft2.
In opposite case, let's say there is a cable tunnel with 30 ft width and 300 ft length. In this case the most remote 2500 ft2 area comes with only 83.3 ft length. Could I design the sprinkler system considering only 83.3 ft length or 100 ft linear length should be considered.
It seems quite specific question, but I think that there are some engineers who have dealt with this kind of matter. Please share your thoughts.