Sprinklers in warehouses: why racking changes everything

Most of what is written about sprinklers assumes an office. Warehouses are a different problem, and the difference is not size. It is that the fire is inside the racking, not on the floor, and everything about the design follows from that.

The design was made once, against three things

A warehouse sprinkler system under BS EN 12845 is designed against a hazard classification, and that classification is set by three inputs:

1. What is stored, the commodity class. Cardboard and paper behave very differently from plastics, aerosols, foam and packaged flammables.
2. How high it is stored. Storage height is a direct input, not a detail.
3. How it is arranged: open floor, block stacked, palletised racking, and how the aisles run.

Those three fixed the design density, the assumed area of operation and the water supply duration on the day the system was designed. They are then almost never revisited, while the business changes all three.

The three changes that quietly break a design

Racking gets taller

The cheapest way to add capacity is upwards, and nothing about it looks like a fire safety decision. Raise the top beam by a metre and the storage height changes, which changes the classification, which changes the density the system needed to deliver.

The system does not become dangerous overnight, and it will still operate. It may simply no longer be able to control a fire in the load it now has to reach.

The commodity changes

A third-party logistics operator taking on a new contract can move from paper goods to plastic-packaged consumer goods in a fortnight. The building is identical. The fire is not: plastics burn hotter, faster and with far more heat release, and the water needed to control them is substantially greater.

Racking is added where there was none

A section designed as open floor, with roof-level sprinklers spaced for open floor, gets racked out. Now there is a load between the sprinkler and the fire, and the water that used to reach the floor lands on the top of a pallet.

Roof-level, in-rack and ESFR

Three ways of getting water to a fire in a rack, and warehouses use all of them.

Standard roof-level sprinklers. Adequate up to certain storage heights and commodity classes. Past that, the plume from a rack fire is strong enough that water from the roof does not get down through it.

In-rack sprinklers. Heads and pipework mounted inside the racking, at one or more tiers, attacking the fire where it is. They work well and they are exposed: forklift damage to in-rack pipework is one of the most common causes of accidental discharge in warehousing. Guards help. Driver awareness helps more.

ESFR. Early Suppression Fast Response heads at roof level: large orifice, fast-response element, designed to drive enough water through the plume to suppress the fire rather than merely control it. Where the conditions allow it, ESFR removes the need for in-rack sprinklers entirely, which is why it dominates modern distribution buildings.

Those conditions are strict. Roof height and profile, obstructions such as ductwork and lighting, aisle widths and storage arrangement all constrain it, and an ESFR design is invalidated more easily than people expect by services installed under the roof afterwards.

What obstructs a warehouse system

The most common real-world faults we find in warehouses are not mechanical. They are things put in the way.

• Stock stacked too close to the heads. There is a required clearance below a sprinkler, and a pallet stacked into it does not just block that head, it disrupts the spray pattern for the ones around it.
• Services installed under the sprinklers. New lighting, ductwork, cable tray and conveyor lines fitted after commissioning, sitting between the head and the floor.
• Mezzanines added without sprinklers underneath. A mezzanine creates a new ceiling, and the space under it is now unprotected.
• Racking changed without the layout being reviewed. Aisles moved, so the head layout no longer relates to the aisles.

None of these appears on a service report as a fault, because none of them is a fault in the system. They are faults in the relationship between the system and the building, and they need somebody looking at both.

What to do about it

The annual service proves the system works as designed. It does not prove the design still fits the building, and no service regime will tell you that. Those are different questions and they need asking separately.

A practical rule for anyone running a warehouse:

• If storage height, commodity or racking layout has changed since the system was designed, have the design reviewed. Not the system serviced. Reviewed.
• Tell your insurer. Commodity class is priced. Finding out at a claim that the stored goods were outside the design is the worst possible time.
• Walk the floor once a year looking upwards, at clearances, at obstructions and at anything installed under the sprinklers since last time.

The maintenance side of it, the intervals and what each visit covers, is BS EN 12845 in plain English and sprinkler servicing intervals.

Most of the buildings we look after are warehouses and distribution units, and the survey is free. If any of the three changes above has happened on your site, that is the conversation worth having, and it is sprinkler servicing or a design review under design and installation depending on what it turns up.