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Obstructions and ESFR Sprinklers Protecting Light & Ordinary Hazard Occupancies
You asked the following questions: “Sections 8.4.6.6 and 8.4.7.3 allow ESFR and CMSA sprinklers to protect light and ordinary hazard occupancies. While Section 8.5.5.3.3 requires sprinklers of the same type under obstructions as installed at the ceiling Section 8.5.5.2.2 requires that minimum distances and special requirements of Sections 8.6 through 8.12 to be followed with regards to truss webs, and chords, pipes, columns, and fixtures. Without addressing obstruction criteria for CMSA and ESFR sprinklers in light and ordinary hazard occupancies, the obstruction criteria in Sections 8.11.5.3 and 8.12.5 still seem to govern although they would normally be expected to be installed in storage occupancies. In a light or ordinary hazard occupancy, although it is not stated, would it be reasonable not to require additional sprinklers below obstructions that are 4 ft. or less in width as long as the spray pattern can fully develop? Given the volume of water CMSA and ESFR systems are designed to deliver and the significantly lower fuel loads and rates of heat release expected in a light or ordinary hazard occupancy, it would seem reasonable to expect control (for CMSA) or suppression (for ESFR) of fires. This can be expected as long as the sprinkler spray pattern is allowed to fully develop where deflector clearances of 36 in. above the top of an obstruction can be provided.” In response to your question, we have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is the when using CMSA and ESFR sprinklers the obstruction requirements for those sprinklers shall apply. Sections 8.4.6.6 and 8.4.7.3 were added for situations where an existing warehouse with an ESFR or CMSA sprinkler system is being converted to a light or ordinary hazard occupancy. The intent was not for new construction since ESFR and CMSA sprinklers are specifically designed for storage occupancies. This is explained in the commentary for these section in the NFPA 13 Handbook. This is further supported by the lack of requirements in Sections 8.11 and 8.12 requiring that Section 8.5 shall apply unless modified by these sections. Typically, if the standard intended for us to apply the standard spray sprinkler obstruction requirements when protecting light or ordinary hazard occupancies both Sections 8.11 and 8.12 would send us back to Section 8.6. Instead, specific requirements in Sections 8.11 and 8.12 are to be followed. Both chapters have their own requirements regarding obstruction based on fire testing results. This is due to both types of storage sprinklers being far more sensitive to obstructions, affecting the spray pattern and potentially cold soldering adjacent sprinklers. For example, pendent ESFR sprinklers are designed with a hole in the middle of the deflector. This provides a thrust in the center of the discharge pattern that forces a stronger flow of water in the middle. When even small continuous obstructions are directly beneath the deflector, it destroys the discharge pattern for that sprinkler. Section 8.12.5.3.1(2) defines continuous obstructions as objects that are 2 in. or less in width and that are located a minimum of 2 ft. below the elevation of the sprinkler deflector or that are positioned a minimum of 1 ft. horizontally from the sprinkler. Even worse, the water bouncing off these objects can cause adjacent sprinklers to cold solder, keeping them from activating. Factory Mutual did a full-scale fire test that defined these parameters. Since the initial ESFR sprinkler was rendered ineffective by the obstruction and the adjacent sprinklers were effectively removed from attacking the fire, the test opened 27 sprinklers before they manually suppressed the fire. An impressive failure caused by one small obstruction. Thus, when using CMSA and ESFR sprinklers the obstruction requirements for those sprinklers shall apply not matter what the occupancy classification may be. It also bears repeating that CMSA and ESFR sprinklers are storage sprinklers and are not to be used for new construction of light and/or ordinary hazard occupancies.
