ESFR Warehouse: Storage Clearance and a Duct Obstruction
A 200 ft by 300 ft single-story warehouse has a 32 ft ceiling and ESFR pendent sprinklers, K=25.2, with deflectors 6 in below the roof deck. Storage is 25 ft high and contains Group A unexpanded plastic in corrugated cartons. A 48 in wide by 24 in deep HVAC duct runs parallel to a branch line; its bottom is 28 ft above the floor, and storage is loaded under it. The contractor proposes to omit sprinklers below the duct because the duct is open on both ends and to reuse the existing 6 in riser. The local water supply has not been retested since the shell building was constructed. The owner asks whether the ESFR layout, obstruction handling, and riser are acceptable for final inspection.
1. Evaluate the deflector-to-storage clearance and whether the ESFR design is suitable for this storage arrangement.
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ESFR protection depends on a minimum clearance between the deflector and the top of storage, commonly 36 in. Here the deflector is at approximately 31.5 ft and storage is 25 ft high, leaving about 6.5 ft (78 in) of clearance, so the basic clearance criterion is met.
The ceiling height and storage height must still fall within the specific sprinkler listing for Group A unexpanded plastic, K=25.2, and the proposed spacing. ESFR is not a generic drop-in: the manufacturer's listing must cover the commodity, storage height, ceiling height, and sprinkler spacing. A 6 in deflector distance below the deck is generally within ESFR listing ranges, but the reviewer should confirm it against the submittal rather than assume it.
2. The 48 in wide duct is 24 in deep and its bottom is 28 ft above the floor, with storage underneath. May the contractor omit sprinklers below the duct? Explain the obstruction analysis.
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No. A 48 in wide duct is 4 ft wide, which reaches the threshold at which NFPA 13 obstruction rules require protection below or a compliant alternative. The duct bottom at 28 ft is only 3 ft above the 25 ft storage and about 3.5 ft below the deflectors. ESFR spray patterns need open space to develop; a duct that wide and deep directly over storage will block the spray.
Open ends do not cure the obstruction. The contractor must either relocate the duct, provide sprinklers below the duct if the listing and design permit it, or submit an approved alternate layout. The storage under the duct also must maintain the required clearance to the duct and sprinklers. The reviewer should not accept omission based only on duct width or open ends.
3. What must be verified about the existing 6 in riser and the water supply before the system can pass final inspection?
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A 6 in riser may be adequate, but it cannot be accepted by rule of thumb. The contractor must provide a hydraulic calculation using the ESFR sprinkler demand, including K-factor, minimum operating pressure, number of sprinklers calculated, elevation, friction loss, backflow preventer, meter, and fittings.
The water supply also needs a current flow test; the shell-building test is stale. The reviewer should compare the calculated demand point to the supply curve, verify the riser and underground main can deliver the required flow at the required pressure, and confirm hydrostatic testing, flushing, alarm and inspector's test connections, main drain, and FDC. Final acceptance requires the actual installed layout to match the approved submittal.