Sprinklers - 18-inch Rule

What is the basic premise behind the "18-inch rule for fire sprinkler head clearance"?

Any examples are for illustrative purposes only. 

The 18-inch applies only to areas that have sprinklers installed.
Picture a horizontal plane parallel to the ceiling that is 18 inches below the sprinkler heads.   Nothing should be in that area between the bottom of the sprinkler heads and the imaginary horizontal plane parallel to the ceiling that is 18 inches below.  This is done to allow an even and unobstructed spray pattern from the sprinklers when triggered to extinguish the fire.

Perimeter wall shelving and storage are allowed to extend from floor to ceiling level. 

Additional Resources: 
LS.02.01.35
NFPA 13-2010
Last updated on May 20, 2020
Manual: Behavioral Health
Chapter: Life Safety LS

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