Sprinkler Protection in a Racked Warehouse
A single-storey warehouse 9 m to the underside of the roof is being converted to racked storage. The existing sprinkler system is a wet-pipe installation with upright sprinklers at roof level on a 4 m grid, designed for a light-hazard occupancy. The new racking will be 7.5 m high, leaving 1.5 m between the top of storage and the roof sprinklers, and will hold cartons of packaged goods in solid shelves. The owner wants to keep the existing roof system and add nothing, arguing the roof sprinklers still cover the whole floor. A tenant's insurer has asked for a review before occupancy.
1. Assess whether the existing roof-level sprinkler arrangement is adequate for the proposed storage and explain the main concerns.
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It is not adequate. The existing system was designed for a light-hazard occupancy, but 7.5 m of racked packaged goods in solid shelves is a substantially higher hazard, and the roof-level uprights on a 4 m grid cannot deliver the density or the coverage that this storage demands. The 1.5 m gap between the top of storage and the roof sprinklers is a particular problem: with solid shelves, fire within the rack is shielded from roof-level water, so the roof heads may not operate until the fire has grown well beyond their design. Water from roof sprinklers also tends to be deflected by the rack tops and does not reach the seat of the fire.
The design must be re-evaluated against the applicable storage sprinkler standard for the commodity class, storage height and rack arrangement. In-rack sprinklers, or a combination of roof and in-rack protection, are typically required, and the roof system may need a higher density, closer spacing or a different head type. The 1.5 m clearance may also be below the minimum required between the deflector and the top of storage, which is a separate non-compliance.
Keeping the existing system unchanged would leave the building outside its design basis and likely breach the insurer's conditions.
2. The owner asks whether adding in-rack sprinklers alone, without changing the roof system, would solve the problem. Advise, giving your reasoning.
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In-rack sprinklers alone do not solve it. In-rack heads control fire at the level where it starts, but they are designed to work with roof-level protection that handles the plume and any fire that reaches the top of the rack. Removing or ignoring the roof system's role leaves the upper storage and the space above the racks unprotected, and the roof system as installed is still designed for a light hazard that no longer applies.
The correct approach is a single coordinated design: determine the commodity classification and the rack configuration, then select a protection scheme from the applicable standard that sets roof density and spacing together with in-rack levels and clearances. The 1.5 m gap must be checked against the minimum clearance for the chosen head type; if it is too small, the storage height or the roof arrangement must change.
Advise the owner that this is a design change requiring a competent fire engineer and, in most jurisdictions, approval from the authority and the insurer before occupancy. A partial addition without re-designing the roof system would create a system that looks compliant but is not, which is worse than an acknowledged deficiency.