EN 12845 Intermediate Level Sprinklers in High Hazard

When ceiling sprinklers alone are no longer enough: the intermediate level arrangement, water shields and the combined hydraulic calculation, explained from site logic.

On a textile central warehouse, the ceiling was at 11.5 m and the top of racking at 8.2 m. The architect wanted to grid the ceiling sprinklers and close the project — "they'll spray from above anyway". The commodity table says otherwise: above 8 m for Category II palletised storage, ceiling-only protection is no longer valid. Either the density rises steeply, or in-rack sprinklers go into the racking. The whole story of the in-rack clause starts exactly there — when the ceiling runs out, you go down into the rack.

When are intermediate level sprinklers mandatory?

The standard closes off this requirement from three directions:

• Storage height exceeded: once the ceiling-only maximum storage height in the commodity table for ST1–ST6 is exceeded, in-rack sprinklers become mandatory automatically.
• Excessive clearance: where the distance between the ceiling sprinkler deflector and the top of storage exceeds 4 m, there are two options — increase the density by 2.5 mm/min for the first excess metre and 1 mm/min for each subsequent metre (with a minimum of K115), or install intermediate in-rack sprinklers.
• Rack configuration: in palletised racking, drive-through racking and ST5/ST6 shelving, geometry makes it mandatory in any case.

Mezzanines and suspended platforms bring the requirement in through the water shield clause: where sprinklers exist below, water from above risks wetting the bulb, so a shield becomes mandatory.

Ceiling height versus storage height

This is the parameter most often confused on site. EN 12845 measures not the ceiling level itself but the clearance between the ceiling sprinkler deflector and the top of storage. The logic is simple: the higher the sprinkler discharges from, the more the water is deflected sideways and the greater the chance of horizontal fire spread.

Clearance	EN 12845 approach
≤ 4 m	Ceiling-only acceptable; the tabulated density applies directly.
> 4 m (option 1)	+2.5 mm/min for the first metre, +1 mm/min for each further metre; minimum K115.
> 4 m (option 2)	Install intermediate in-rack sprinklers.

The practical decision: once clearance passes 5–6 m, option 1 escalates quickly — larger K-factor, larger pump, larger pipes. Option 2, the intermediate levels, is almost always more economical.

In-rack versus intermediate — a terminology note

The standard uses two names for the same concept:

• In-rack sprinkler: a sprinkler placed inside the rack volume. A description of position.
• Intermediate level sprinkler: a row placed at particular levels through the storage height, generally per tier or every 3.5 m. A description of function.

In high-hazard storage every intermediate level sprinkler is an in-rack sprinkler, but not every in-rack sprinkler is an intermediate level head. EN 12845-2 defines additional in-rack rules for ESFR systems separately.

Vertical and horizontal layout

The golden rule: the vertical distance from floor to the first intermediate level, and between levels, may not exceed 3.50 m or two tiers, whichever is less. The topmost intermediate level may not be lower than one tier below the top storage level; otherwise the upper tiers are left unprotected.

Horizontally it depends on commodity category:

Commodity category	Horizontal spacing	Horizontal × vertical product	Notes
Category I, II	≤ 3.75 m	≤ 9.8 m²	At every second transverse flue intersection; rows staggered.
Category III, IV	≤ 1.90 m	≤ 4.9 m²	At every transverse flue intersection; closer spacing.

Geometric constraints apply too: the longitudinal flue (back-to-back gap) must be at least 0.15 m and the transverse flue at least 0.1 m. Without pallet stops, pallets overhang into the flue and water penetration ends — the sprinkler opens into nothing.

Water shields

Projects that overlook this clause get a surprise at commissioning. When an upper-level sprinkler opens, some of its water falls on the bulb of the sprinkler below — cooling it, delaying operation or preventing it entirely. EN 12845 is explicit: every sprinkler inside racking, beneath perforated shelving, below a platform or below a mezzanine needs a metal water shield at least 0.075 m in diameter.

Field practice:

• On upright heads the shield is not attached directly to the deflector or yoke, but held on a separate bracket so the distribution is not disturbed.
• On pendent installations the shield is usually part of the body (intermediate-level pendent models).
• Every intermediate level needs shields; only the topmost level may be left without, since nothing sits above it.

The combined hydraulic calculation

Where intermediate level sprinklers exist, fully calculated design is mandatory and the pre-calculated table method is prohibited. The two loads are not stacked; both are calculated simultaneously:

• Ceiling sprinklers: a minimum density of 7.5 mm/min over a 260 m² area of operation. Where goods are stacked above the topmost intermediate level, the density comes from the higher table.
• Intermediate level sprinklers: three sprinklers assumed open at the hydraulically most remote position, on a maximum of three levels simultaneously. Aisle width determines how many racks are involved:

Aisle width	Racks active in the calculation
≥ 2.4 m	1 rack
1.2–2.4 m	2 racks
< 1.2 m	3 racks

A minimum of 2.0 bar is required at every operating sprinkler. Where there are more than 50 intermediate level sprinklers, a separate control valve set is mandatory — they cannot be fed from the same alarm valve as the ceiling system.

Worked example — 8 m racking, Category II palletised

A typical textile or packaging warehouse:

• ST4 multiple-row drive-through racking, top of storage 8.0 m, ceiling 11.0 m, clearance 3.0 m.
• The ceiling-only limit for Category II in ST4 is around 5 m at 10 mm/min; 8 m exceeds it, so intermediate levels are mandatory.
• Tier height 1.8 m → a level every two tiers would be 3.6 m, exceeding the 3.5 m limit, so the geometry must be redivided.
• Practical solution: intermediate levels at 2.5 m and 5.0 m plus the 11.0 m ceiling. The gap between the top intermediate (5.0 m) and top of storage (8.0 m) is more than one tier, so a third level goes in at 6.5 m — three intermediate levels plus the ceiling.
• Horizontally: for Category II, every second transverse flue intersection, at a maximum spacing of 3.75 m.
• Hydraulics: with a 2.1 m aisle, two racks are active × three levels × three sprinklers = 18 intermediate heads calculated simultaneously, alongside 7.5 mm/min over 260 m² at the ceiling.

Doing that by hand takes a long time because of the pipe size iteration; a storage module that combines ceiling and intermediate levels in one calculation is the practical route.

Comparison with NFPA 13 in-rack protection

Item	EN 12845	NFPA 13
Vertical spacing	≤ 3.5 m or 2 tiers	Typically 3.05 m (10 ft) or per tier
Sprinklers in the calculation	3 sprinklers × up to 3 levels	6 or 8 sprinklers on a single level for Class III/IV
Horizontal spacing (Cat. III/IV)	≤ 1.9 m	≤ 1.52 m (5 ft)
Water shield	Min. 0.075 m metal disc	Min. 76 mm (3 in) — equivalent
Ceiling density	Min. 7.5 mm/min over 260 m²	Class-density curve

NFPA assumes more sprinklers operating simultaneously on a single level (six to eight); EN 12845 assumes fewer but across three levels. Total flow ends up comparable, so the difference does not greatly affect pump sizing.

Turkish practice

BYKHY specifies "TS EN 12845 or NFPA 13" for sprinkler systems — pick one and follow it through. In high-hazard storage facilities, particularly e-commerce logistics warehouses, textile central stores and automotive parts centres, the intermediate sprinkler decision has to be taken at the start of the project. The steel rack manufacturer and the sprinkler contractor need to talk first; otherwise, running in-rack pipework after the racking is erected means drilling, clamping and re-dimensioning flues.

It also matters for insurance: on FM-compliant facilities, ceiling-only protection is not accepted above 4 m clearance, and intermediate levels or ESFR are required. A surveyor's note reading "intermediate level sprinkler not provided" doubles the premium.

Common errors

• Treating the 4 m clearance rule as ceiling-to-floor. It is deflector to top of storage; change the racking and the calculation changes.
• Skipping water shields. The lower sprinkler fails to open at commissioning and the client rejects the report.
• Closing with a pre-calculated table. Explicitly prohibited; fully calculated design is mandatory.
• Connecting intermediate levels to the ceiling valve. Above 50 heads, a separate valve is mandatory.
• No pallet stops. Pallets overhang the flue and water penetration falls to zero.
• Leaving the top tier unprotected. The topmost intermediate level may not sit more than one tier below the top of storage.

Check list

• Is clearance above 4 m? A cost comparison of both options has been made.
• Has the commodity category (I–IV) been correctly established from the classification annexes?
• Is vertical spacing within 3.5 m and two tiers?
• Is the horizontal × vertical product within 9.8 m² for Categories I/II and 4.9 m² for III/IV?
• Are water shields (minimum 75 mm diameter) drawn on every intermediate head?
• Is the hydraulic calculation fully calculated, with at least 2.0 bar at every operating sprinkler?
• Above 50 intermediate heads, is a separate alarm valve group shown on the drawings?
• Longitudinal flue ≥ 0.15 m, transverse flue ≥ 0.1 m, pallet stops in the design?
• Have quick-response intermediate sprinklers been selected?

Frequently Asked Questions

What triggers intermediate level sprinklers?

Exceeding the ceiling-only storage height for the commodity and configuration, more than 4 m of clearance between deflector and top of storage, or a rack configuration that requires them geometrically.

Is the 4 m clearance measured from the ceiling?

No — from the sprinkler deflector to the top of storage. Change the racking and the calculation changes with it.

How many intermediate heads enter the calculation?

Three per level across a maximum of three levels, on one, two or three racks depending on aisle width — up to 27 in a narrow-aisle layout.

Why is a water shield mandatory?

Because water from an upper head cools the bulb below, delaying or preventing its operation. A metal shield at least 75 mm in diameter is required on every in-rack head.

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