sprinklernotes
Sprinklers Under Obstructions “Section 8.5.5.3 along with section 8.5.5.3.1 seem to indicate that the minimum required clearance for obstructions 4 ft or less in width is any distance over 18-in. below the deflector and that if that distance is maintained, sprinklers are not required below the obstruction. Section 8.6.5.2.1.3 seems to indicate that if the sprinkler is less than 24 in. from the obstruction, the 3-times rule must be applied, which seems to imply that an obstruction that is less than 4-ft wide and more than 18in. below the deflector, but less than 24-in. above the obstruction, would require sprinklers below the obstruction. Please clarify how these requirements are to be applied.”
We have reviewed NFPA 13, Standard for the Installation of Sprinkler Systems, 2016 edition as the applicable standard. Our informal interpretation is if the obstruction that is less than 4 ft in width is positioned more than 18-in. below the sprinklers deflector we can ignore it. These two sections both states that sprinklers are not required for obstructions located more than 18-in. below the sprinkler deflector if the obstruction is not greater than 4 ft in width. This application has the ceiling sprinklers located well above the required 18-in. clearance. Thus, the distribution pattern from the sprinklers will be fully developed by the time it reaches the obstruction. The 4-ft width is intended to apply to the lesser dimension. For example, a light fixture measures 1 ft by 8 ft where the 8-ft dimension is not considered for the application of the obstruction rules in section 8.5.5.3.1. So, a shadow may extend the full length of the obstruction and may not apply an even coat of water on the floor. This is considered acceptable since sprinkler systems are designed to control the fire and allows time for the responding fire service to finish the job. Now, if the obstruction was within 18 in. of the deflector, we would have to apply the requirements of section 8.6.5.2.1.3.
