Warehouse ESFR Design With High-Piled Group A Plastics
A Minnesota contractor is designing a new 30,000 sq ft single-story warehouse with a 32 ft ceiling. The owner plans to store cartoned, unexpanded Group A plastics in double-row racks to a height of 25 ft. The contractor proposes ceiling-only ESFR pendent sprinklers, K-14.0, spaced 10 ft by 10 ft on branch lines, with 12 sprinklers per branch line. The contractor states that ESFR design eliminates the need for in-rack sprinklers and submits a hydraulic calculation using 12 sprinklers at 50 psi. The public water supply has a static pressure of 175 psi and a residual pressure of 55 psi at 1,200 gpm. The building has 18 in deep steel girders running parallel to and 6 ft from branch lines. The AHJ has not yet reviewed the storage arrangement.
1. Can the contractor rely on ceiling-only ESFR sprinklers and omit in-rack sprinklers? Give the decision path the reviewer should follow.
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Not on these facts alone. ESFR is a listed design concept, not a blanket exemption from in-rack sprinklers. The reviewer must first classify the commodity and confirm the storage height, aisle width, rack arrangement, ceiling height, and sprinkler listing. Cartoned unexpanded Group A plastics are a higher-challenge commodity; ESFR ceiling-only protection is limited to the specific commodity, storage, and ceiling combinations recognized in the listing and the adopted NFPA 13 criteria. If the arrangement falls outside those limits, the designer must provide in-rack sprinklers or another compliant scheme. The 18 in girders also trigger an obstruction analysis. Approval should be withheld until the designer documents that the exact storage configuration is within the ESFR listing and the adopted standard, and until the obstruction and hydraulic issues are resolved.
2. What hydraulic and submittal information must be resolved before the AHJ can approve the design?
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The submittal must show more than a 12-sprinkler calculation. It should include the design basis, commodity classification, storage arrangement and heights, sprinkler listing and temperature rating, deflector position, remote-area location, number of design sprinklers, discharge pressure, hose allowance, and the water supply curve. The contractor must prove that the 55 psi residual at 1,200 gpm can satisfy the calculated demand with the required safety margin, including any inside and outside hose streams. Cut sheets for the ESFR sprinkler and calculations for the most demanding branch line are needed. If the supply is inadequate, the contractor must propose a fire pump, water storage, or a different compliant design rather than simply reducing the calculation.
3. The girders are 18 in deep and 6 ft from branch lines. How should the contractor address them?
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The contractor cannot assume the girders are acceptable because they are structural. ESFR sprinklers have strict obstruction rules because the spray pattern must reach the storage. The designer should perform an obstruction analysis using the adopted standard and the sprinkler listing, then either relocate branch lines or sprinklers, adjust deflector height, or use a listed arrangement that maintains the required clearance and spray pattern. Field changes made after approval are not a substitute. The revised drawings and calculations should be submitted to the AHJ, and the installer should verify final dimensions before rough-in inspection.