The question I am inquiring about pertains to a fire station in which the apparatus bays are to be calculated at an FM Global criteria of 0.20 g.p.m. per square foot over a design area of 3,500 square feet following the calculation procedures of the 2013 Edition of N.F.P.A. #13. Room Design Method is specifically prohibited on this project. The remote area in question consists of two apparatus bays with CMU walls separated by Ordinary Hazard spaces approximately 17'-0" wide, see image below for a concept of the area of question.
The Apparatus Bays are required to be protected with a dry pipe automatic fire protection sprinkler system with a wet pipe automatic fire protection sprinkler system protecting the remainder of the building. The Original sprinkler system design that was submitted for review, had both the Apparatus Bays and Ordinary Hazard spaces protected by a single dry pipe automatic fire protection sprinkler system. The design area was limited to the largest Apparatus Bays only with flows being added per the procedures outlined in Section 220.127.116.11.1.4 of the 2013 Edition of N.F.P.A. #13 (18.104.22.168.4 in the 2016 edition) to equal the 700 g.p.m. minimum demand based upon the 0.20 density over a 3,500 square foot design area.
A previous informal interpretation that we submitted concurred that walls are not to be considered when determining the remote area using the density/area approach to hydraulic calculations and that the remote area is to be extended into adjacent spaces until the minimum remote area size is fulfilled.
On the resubmittal of this project, the sprinkler protection of the Ordinary Hazard spaces has now been changed from the dry pipe automatic fire protection sprinkler system to being protected by the wet pipe automatic fire protection sprinkler system. This approach essentially divides the Apparatus Bays into two separate dry system areas.
It is our understanding from previous discussions on this type of situation, that the minimum remote area size is not isolated to a single system and that sprinklers located on the wet pipe automatic fire protection sprinkler system would be included in the hydraulic calculations. Would the remote area in this particular case be isolated to the dry system in the largest Apparatus Bay only or would it consist of sprinklers from both the dry and wet systems?