Question

1. Residential sprinklers installed in accordance with NFPA 13 – 2019 must discharge with a minimum density of:

   	A.	0.05 gpm/sq ft
   	B.	0.1 gpm/sq ft
   	C.	18 gpm for a 12’ x 12’ area for a single sprinkler
   	D.	13 gpm for a 12’ x 12’ area for a single sprinkler

Answer 1

B. 0.1 gpm/sq ft

The building is not designed to open up every sprinkler head in the building. As more sprinkler heads open, you lose water pressure in a building. This diminishing pressure results in a failure in the sprinkler system. Testing laboratories have conducted full-scale fire tests to provide criteria for different occupancies and hazards. A design density is comprised of two numbers:

• Amount of water provided per square feet (gallons per minute/gpm per square feet) in the remote area
• The size of the remote area. It is the maximum area in which the fire is controlled and/or extinguished based on testing

The above two factors dictate a design density. For example an office requires a light hazard design density (i.e. 0.1 gpm per sq foot over the most remote 1500 square feet). This means that tests have shown that if 0.1 gpm per square of sprinkler water is delivered over 1500 square feet, the fire can be controlled in an office until the fire department arrives and extinguishes the fire.

What does 1500 most remote area mean? The term remote area is referred as the hydraulically most remote area. It is basically the area furthest from the water source into the building. If a minimum of 0.1 gpm is provided in the area in the building that is hydraulically furthest from the water source (worst case area in the building), then the sprinkler system in the remainder of the building can produce at least 0.1gpm/sq ft or more in any other 1500 sq ft in the building. If the fire grows beyond the designed square footage, the gpm/sq ft (first number) will disintegrate to less than what is designed, which would most likely result in a failure of the sprinkler system.