Sprinklers - 18-inch Rule

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

The 18-inch rule does not apply to a non-sprinkled space. If the space is sprinkled, picture a horizontal plane parallel to the ceiling, below ceiling level at the discharge of the ceiling mounted sprinkler heads. Then picture a parallel horizontal plane 18 inches below that sprinkler head discharge plane. Nothing, to include shelving, racks, storage, etc., can be within 18 inches of the sprinkler head discharge plane unless against a perimeter wall. There is to be no obstructions to sprinkler discharge pattern development. Perimeter wall shelving and storage are allowed from floor to ceiling level. Sprinkler heads cannot be within 4 inches on a vertical plane from a wall, perimeter shelving or other vertical obstruction. The 2010 edition of NFPA 13 has many intricacies with regard to fire sprinkler spray pattern obstructions, but The Joint Commission uses the criteria defined above for simplicity and clarity.
Last updated on February 22, 2018
Manual: Behavioral Health
Chapter: Life Safety LS

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