ESFR, High-Piled Plastics, and a Marginal Water Supply
An existing 150,000 sq ft warehouse with a 30 ft ceiling has a wet-pipe ESFR system with deflectors 28 ft above the floor. The original design basis was Class IV palletized storage to 20 ft. The new tenant proposes rack storage of cartoned, unexpanded Group A plastics to 26 ft in 8 ft aisles, single-row racks along the walls and double-row racks in the center, including one 20 ft long section of solid shelving. The contractor proposes keeping the existing ESFR grid and adding a diesel-driven 750 gpm fire pump in a 200 sq ft room inside the warehouse. The water supply test at the riser: 60 psi static, 20 psi residual at 1,800 gpm. The building's fire alarm system consists of manual pull stations only.
1. Is the existing ESFR grid acceptable for the proposed storage, and what are the applicant's options?
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Step 1 - Clearance. ESFR sprinklers depend on a high-momentum discharge that reaches the top of storage; the standard requires a minimum clearance between deflector and the top of storage (36 in. for ESFR). At a 28 ft deflector height and 26 ft storage, the clearance is 24 in. That fails, and it fails regardless of density.
Step 2 - Commodity and arrangement. Cartoned unexpanded Group A plastics are within the listing envelope for ESFR only when the storage height, ceiling height, aisle width, and arrangement all fall within the listing. Solid shelving is outside the ESFR ceiling-only concept - sprinkler spray cannot penetrate it - so that section needs in-rack protection, or the shelving must be removed or converted to open shelving.
Step 3 - Options for the applicant. (a) Cap storage at 25 ft (28 ft minus 36 in.) and delete the solid shelving - cheapest and usually acceptable if the listing limits are otherwise met; (b) raise the deflectors or the roof and re-perform the hydraulic design; (c) abandon ESFR and design a control-mode system with in-rack sprinklers for the plastic, which changes the demand substantially.
Step 4 - Reviewer's position. Return the shop drawings. The design must state the commodity class, storage height, aisle width, deflector elevation, and the listing under which the ESFR is applied, and the plans must show in-rack sprinklers wherever solid shelving remains.
2. Does the water supply support the system as proposed, and is the proposed fire pump installation defensible?
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Step 1 - Establish the demand, not the pump size. The pump size is an output, not an input. First determine the required flow and pressure at the base of the riser for the actual storage arrangement, then add the hose stream allowance, then apply the safety margin over the available supply.
Step 2 - Read the supply curve critically. 60 psi static and 20 psi residual at 1,800 gpm describes a supply with significant friction loss - the pressure collapses as flow rises. A single-point test is a snapshot; require a flow test at the actual hydrant elevations, corrected to the riser, before accepting any pump sizing.
Step 3 - Check the pump against the supply. A 750 gpm pump cannot deliver the ESFR demand for this arrangement if that demand is well above 750 gpm plus hose allowance. Oversizing a pump on a weak suction supply pushes the pump toward cavitation and can pull the city main into negative pressure. Verify the pump curve, the net positive suction head, and the churn condition.
Step 4 - Pump room and controls. A fire pump room needs a fire-resistance rating, separation from the warehouse, adequate ventilation and combustion air for a diesel driver, fuel storage and containment, and heating. Two hundred square feet housing a diesel driver is tight; require a layout, and require supervision of pump running, controller trouble, and fuel level by the fire alarm system.
Step 5 - Test header and suction. Confirm the discharge test header can flow the pump at 150 percent of rated capacity without flooding or endangering anyone, and that the suction piping is sized for the flow demand.
3. The building has only manual pull stations. What does this change of use trigger, and what should the reviewer require?
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Step 1 - Treat the tenancy change as a change of use. Higher-hazard, higher-value storage is a change in the hazard being protected; the alarm and detection design basis on the original permit may no longer be valid even though the occupancy label has not changed.
Step 2 - Identify the new required functions. Adding a fire pump brings supervisory requirements: pump running, pump controller in trouble, loss of power, and low fuel or low suction must be annunciated. All sprinkler control valves must be supervised. Waterflow switches must initiate an alarm. None of this exists with manual pull stations alone.
Step 3 - Check whether a system is now required at all. Confirm with the adopted NFPA 101 occupancy chapters whether the building size, height, or occupant load now requires a fire alarm system, and whether the local amendments require monitoring. If the system is required, manual-only is not a compliant substitute.
Step 4 - Require a complete design submittal. Demand a fire alarm sequence matrix and device schedule prepared to NFPA 72, coordinated with the sprinkler and pump submittals, and require that monitoring be by an approved supervising station or a constantly attended location.
Step 5 - Do not approve in fragments. The sprinkler, pump, and alarm packages are interdependent. Approve them as a coordinated package or the building will be occupied with a sprinkler system nobody is supervising.