What are in-rack sprinklers and when are they needed?
In-rack (intermediate level) sprinklers are fitted inside the rack structure, in the flue spaces between loads, where the water from the ceiling sprinklers cannot reach the lower tiers of high-bay storage. All three standards place them at the intersections of transverse and longitudinal flues; the number of levels depends on storage height, tier height and commodity. This tool calculates the layout; the ceiling design, pipe sizes and hydraulic calculation are done separately.
EN 12845: the 3.50 m rule and clause 12.5
- Vertical (12.5.2): floor to the lowest level and between levels at most 3.50 m or two tiers, whichever is less. The highest level may not be more than one tier below the top of storage. Unless all ceiling sprinklers are less than 4 m above the top of storage, a level is also placed above the storage.
- Horizontal (12.5.3): Categories I–II in the longitudinal flue, where possible at every second transverse flue intersection, staggered against the row above; spacing at most 3.75 m and horizontal × vertical at most 9.8 m². Categories III–IV at every transverse flue; at most 1.9 m and 4.9 m².
- Rows (12.5.4, 12.5.5): one row per 3.2 m of total rack width; two rows between 3.2 and 6.4 m, equidistant from the edges.
- Shelving ST5/ST6 (12.5.6, Table 21): above every shelf; at most 2.8 m along the row, two rows for 3.0–6.0 m width.
- Sprinklers: K80 or K115 (Table 37a), quick response (Table 38), metal water shield at least 75 mm in diameter (14.7). The design takes 3 sprinklers per level, up to 3 levels; the number of racks involved depends on the aisle width (7.2.3.3).
FM DS 8-9: IRAS(E) and IRAS(EO)
FM Global selects the horizontal arrangement with the flowcharts in Figs. 5, 5a, 6, 6a and 7. The decision depends on:
- rack type and depth;
- whether the deflector is closer than 150 mm to the load below;
- horizontal barriers;
- solid shelf area;
- whether storage exceeds 7.5 m (25 ft), and the 7.5 m and 9.0 m ceiling heights;
- the commodity.
IRAS(EO) places sprinklers at every other transverse flue, 1.2–3.0 m apart; IRAS(E) at every transverse flue, 0.6–2.4 m apart. The vertical increment follows Fig. 15 by commodity: 7.5, 6.0, 4.5 or 3.0 m, with at most 3.0 m of storage above the top level. In-rack sprinklers are FM Approved, quick response, 70 °C nominal (2.3.4.3). The design comes from Table 12 and the ceiling protection table from Table 13.
NFPA 13-2025: Chapter 25 figures
NFPA 13 gives in-rack arrangements combined with CMDA ceiling sprinklers as figures by commodity and height (25.4.2).
- Levels: for Class I–IV stored 3.7–7.6 m high in single- and double-row racks, one level is required. It goes at the first tier level at or above half the storage height (25.1.8.1); for two levels, one-third and two-thirds are used (25.1.8.2).
- Spacing along the rack: read from the figure. It is 3.7 m for exposed Class I–II, 3.0 m for Class IV and 2.4 m for encapsulated or cartoned commodities.
- Multiple-row racks: the plan area per sprinkler is limited to 9.3 m² (7.4 m² for Class IV).
- Group A plastics: the figures also limit the largest vertical spacing and the storage above the top level.
- Solid shelves: Section 25.3 applies.
- Sprinklers: ordinary temperature, standard or quick response, at least K5.6 (K80). Without horizontal barriers they need water shields (25.1.6).
- Design: the values are in Table 25.4.1.1.
- Over 7.6 m: the 25.4.3 figures limit the largest vertical spacing and the storage above the top level, mostly to 3.0 m. In double- and multiple-row racks most arrangements also need face sprinklers at the aisle faces; the tool leaves their positions to the figure and gives its page number.
For NFPA 13 the tool covers arrangements with CMDA ceiling sprinklers. Arrangements with CMSA and ESFR ceilings (25.5, 25.6), in-rack options independent of the ceiling (25.7) and rubber tyres are not in this version.
Frequently Asked Questions
What is the maximum vertical distance between in-rack levels in EN 12845?
Under clause 12.5.2, floor to the lowest level and between levels at most 3.50 m or two tiers, whichever is less. The highest level may not be more than one tier below the top of storage.
Is a level needed above the top of storage?
In EN 12845 not if all ceiling sprinklers are less than 4 m above the storage; otherwise yes (12.5.2). In FM DS 8-9 at most 3.0 m of storage may remain above the top level (Fig. 15).
What is the difference between IRAS(E) and IRAS(EO) in FM DS 8-9?
IRAS(EO) puts sprinklers at every other transverse flue intersection (1.2–3.0 m), IRAS(E) at every transverse flue intersection (0.6–2.4 m). The flowcharts in Figs. 5–7 decide which is acceptable.
Where does a single in-rack level go in NFPA 13?
Where the figure does not show it, at the first tier level at or above half the storage height (25.1.8.1). For two levels, one-third and two-thirds are used (25.1.8.2).
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