Warehouse protection is a design about the contents, not the building. The same building needs completely different protection when what is stored changes.
Step 1 — Classify the commodity
Classification looks at three inputs:
- The product itself. Non-combustible, combustible or plastic?
- The packaging. Carton, plastic crate, stretch wrap, timber pallet. The same product is a different class in different packaging.
- The pallet. Timber and plastic pallets behave differently; plastic pallets raise the fire load markedly.
NFPA 13 uses Class I to IV and plastics groups; EN 12845 rests on a category system and material factor. Whichever language you use, the classification must be defended with a written justification.
Step 2 — Define the storage arrangement
| Arrangement | Characteristic |
|---|---|
| Bulk | Product stacked directly; little air passage |
| Palletised stacking | Pallets stacked; limited vertical channels |
| Racked | Flue spaces present; rapid vertical spread |
| Drive-in racking | No transverse flues; one of the hardest arrangements |
| Automated storage (ASRS) | Dense, narrow aisles; needs specific assessment |
| Mezzanine and over-rack | Additional protection may be needed at intermediate level |
Step 3 — Measure the heights
Three heights are recorded: the ceiling (deflector) height, the maximum storage height and the clearance between them. Those three numbers determine every subsequent decision and are stated explicitly in the design report. Clearance falling below the standard's minimum is the most frequent breach.
Step 4 — Choose the protection strategy
- Ceiling only (CMDA). Low height and low hazard commodity; the classic density-area method.
- Ceiling only (CMSA). With large drop heads, at defined arrangements and heights.
- Ceiling only (ESFR). Suppression mode; ceiling height, storage height and commodity must stay inside the listing limits.
- Ceiling plus in-rack. Where height or commodity exceeds what ceiling protection can cover.
The decision is read from the listing document: an ESFR head is listed for a particular combination of ceiling height, storage height and commodity class. Going outside that combination invalidates the head.
ESFR is not the cheap option, it is the conditional one. It avoids in-rack sprinklers, but in exchange demands high flow, high pressure, strict obstruction rules and unbroken clearance beneath the ceiling. Where those conditions cannot be met, CMSA plus in-rack can be the more reliable arrangement.
Step 5 — Plan the flue spaces
Longitudinal and transverse flue clearances are part of the design and are protected with pallet stops. Where in-rack sprinklers are used, the flue is also the line on which they sit. If the flue is closed, neither ceiling nor in-rack protection works.
Step 6 — Separate the special commodities
- Aerosols. Level classification and separate protection requirements.
- Flammable liquids. Separate compartment, drainage and a foam assessment.
- Lithium-ion batteries. Separation, cooling capacity and explosion control.
- Idle pallets. Quantity and location limits; ideally stored outside.
- Rubber, tyres and foam products. High fire load and dense smoke.
Step 7 — Calculate the water supply
Warehouse designs are the highest-flow designs there are. The duration follows the hazard class and hose reel and hydrant flows are added. Where the warehouse may later move to a higher hazard commodity, leaving headroom in the water supply is cheaper than the investment made afterwards.
Step 8 — Smoke and heat venting
The interaction between smoke venting and sprinklers is particularly critical in a warehouse. Roof vents opening early can exhaust hot gas and delay sprinkler activation. The venting system's activation logic must therefore be designed together with the sprinkler system and agreed with the authority having jurisdiction.
Step 9 — Hand over the operating rules
- Mark the maximum storage height on the racking.
- Explain the flue rule to staff and fit pallet stops.
- Require notification of commodity or packaging changes.
- Enforce a no-storage rule in aisles and loading areas.
- Limit idle pallet quantities.
- Separate and ventilate the forklift charging area.
- Operate a hot work permit system.
The first three questions at a survey
When assessing a warehouse, ask first: what are you storing today, up to what height, and what does the design report say? If those three answers do not line up, discussing the rest of the system is beside the point.
Frequently Asked Questions
What is the first step in warehouse protection?
Commodity classification. The product, its packaging and the pallet type are assessed together; the same product is a different class in different packaging.
Is ESFR suitable for every warehouse?
No. ESFR is listed for a particular combination of ceiling height, storage height and commodity, and also demands high flow, high pressure and strict obstruction rules.
Which three heights are recorded?
Ceiling (deflector) height, maximum storage height and the clearance between them. Those three numbers determine every subsequent decision.
What is asked first at a warehouse survey?
What is stored today, up to what height, and what the design report says. If those three do not line up, the rest of the system is beside the point.
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Download MEP Calc on the App StoreNFPA 13 (2025) · NFPA 25 · BS EN 12845:2015+A1:2019 · FM Global DS 2-0, DS 8-9. This guide is a general road map; the binding text is the chosen standard itself.