ESFR Design Criteria: The Tables of EN 12845-2 Clause 6.6, Step by Step

Source: EN 12845-2:2024 Clause 6 (EN p. 33-48) and TS EN 12845+A2:2026 Clauses 13.4 and 14.3 (EN p. 98-105).

ESFR design works differently from the CMDA density and area logic of EN 12845: no density is calculated, the k-factor, the number of sprinklers and the minimum operating pressure are read from a table. This article follows the order of EN 12845-2 itself.

Step 1: commodity class and storage configuration

Clause 4 (EN p. 6) requires Annex A to be applied for the determination of FH and HHS. Annex A (normative, EN p. 59) gives both the conversion table from the EN 12845:2015 classes (Table A.1) and the classification flow chart for storage commodities containing plastics (Figure A.1). The classes are HHS1-HHS5 for storage and FH1-FH5 for non storage occupancies.

Clause 6.1 (EN p. 33) sets three critical rules:

• The design is based on the design tables in Clause 6. Interpolation and extrapolation are not permitted.
• Where more than one single pallet load of a higher category is stored within any 300 m², the design is based on that higher category.
• Commodities not covered by the design tables (such as flammable liquids, aerosols and their single pallet loads) shall not be protected in accordance with this document; EN 12845 is applied as far as it is applicable.

The same clause states that, unless otherwise indicated, the HHS3 protection category is used for HHS1 and HHS2, that the protection of higher categories may be used to protect lower categories, and that a k-factor design given for a particular ceiling height may also be applied to a lower ceiling height provided no other parameter changes.

Clause 6.2 (EN p. 33): ESFR and CMSA protection shall not be applied to FH3-FH5 occupancies. Where they are used for FH1 and FH2 hazards, they are designed as HHS1-HHS3 in accordance with 6.6 or 6.7, independently of the storage category.

Step 2: suitability of the building

Before moving to the design table, the limits of Clause 5.2 have to be met:

Step 3: placement

Clause 5.1.3.2 (EN p. 8): minimum spacing 2.4 m; maximum spacing 3.7 m for ceilings ≤ 9.1 m and 3.1 m for ceilings > 9.1 m; maximum area per sprinkler 9.3 m², minimum area 6 m²; distance to a wall at most 50 % of the maximum spacing. Clause 5.1.3.5.2 and Table 2 (EN p. 9-10): the deflector at least 100 mm below the ceiling; the maximum vertical distance of the thermal element is 325 mm for ESFR K200, K240 and K400 and 425 mm for K320, K360 and K480. Clause 5.1.3.7 (EN p. 12): a clear space of at least 1 m between the deflector and the top of the storage.

Step 4: choosing the design table

Clause 6.6.1.1 (EN p. 35): Table 7 gives the design criteria for ESFR ceiling only protection and is based on the ceiling height; the designs are generally based on 12 heads. For this table, Clause 5.2.6.1 (horizontal air flow) and Clause 5.3.3.2.2 (obstructions above racks) do not apply. Table 8 belongs to rubber tyre storage and Table 9 to roll paper storage stored on end and free standing.

Table 7, minimum pendent operating pressures (bar), EN p. 36:

Footnotes: the minimum aisle width is 1.8 m in the 15.2 m row and 2.4 m in the 16.8 m / K400 row. The HHS5 rows apply only to exposed expanded plastics and only where all the additional requirements (including the vertical barriers) are applied.

Tables 10 and 11 (designs with special requirements, EN p. 41): these tables are used together with the additional conditions of Clause 6.6.1.2 and give the number of sprinklers along with the pressure. Examples: HHS1-HHS3, ceiling 7.6 m, K200, 9 sprinklers at 2.4 bar; ceiling 12.2 m, K360, 9 sprinklers at 2.8 bar; HHS4, ceiling 9.1 m, K200, 15 sprinklers at 3.5 bar; HHS5, ceiling 12.2 m, K360, 20 sprinklers at 5.2 bar. Table 11 gives the K320, K360, K400 and K480 designs for ceiling heights of 15.2 m and 16.8 m, together with columns for the distance from the ceiling to the thermal element (325 or 425 mm) and the minimum aisle width (1.8 or 2.4 m).

The additional conditions of Clause 6.6.1.2 (EN p. 38): all requirements shall be met for the tables to be applied; Clause 5.2.6.1 always applies (it is no longer optional); where there is an obstruction above rack storage, the recommended approach of 5.3.3.2.2 is applied; the minimum design area shall be 71 m²; the 9 sprinkler design area is 3 sprinklers on each of 3 adjacent range pipes and the 10 sprinkler design is that plus 1 sprinkler on a further range pipe; and the ceiling is non-combustible and preferably unobstructed.

Step 5: duration and the shape of the design area

Table 6 (EN p. 34): for designs of 9, 10 and 12 sprinklers the duration of supply is 60 min; for 15 and 16 sprinklers 90 min; for 20, 24, 25 and 30 sprinklers 120 min. The shape of the design area is 4 × 3 for 12 sprinklers, that is 4 sprinklers per range pipe on 3 range pipes; 3 × 3 for 9 sprinklers; 5 × 3 for 15 sprinklers; 5 × 4 for 20 sprinklers.

Where the range pipes carry fewer sprinklers than the stated number, all the sprinklers are assumed to operate and the number of range pipes covered is increased to compensate. A favourable design area is not required, and pipe size reductions to limit the demand of a favourable hydraulic area are not permitted.

Step 6: hydraulic calculation

The flow formula is in EN 12845 Clause 14.3 (EN p. 104-105): Q = K√P, with Q in litres per minute and P in bar.

Example (arithmetic from the standard's values): HHS1-HHS3, ceiling 13.7 m, storage 12.2 m, K360 pendent. Table 7 gives a minimum of 2.8 bar.

• Per sprinkler, Q = 360 × √2.8 ≈ 602 L/min
• For 12 sprinklers the total is ≈ 7 229 L/min
• According to Table 6 the duration of a 12 sprinkler design is 60 min, so the required volume is ≈ 434 000 L, that is about 434 m³

The location of the design area is determined in accordance with EN 12845 Clause 13.4.2 (EN p. 99): the hydraulically most unfavourable position is found by taking account of all possible positions, together with changes in sprinkler spacing, layout, level, range pipe centres, sprinkler orifice size and pipe diameters.

Step 7: combining ceiling and in-rack protection

Clause 6.6.2 defines two different schemes:

• 6.6.2.1.1 (EN p. 42): for ceilings up to 13.7 m, commodities up to HHS4 in open frame racks (STC4.1-STC4.3); K200 or larger pendent ceiling ESFR sprinklers plus a single level of in-rack sprinklers in the longitudinal flue space only. The in-rack demand is added to the ceiling demand; the water supply is at least 60 min. The in-rack hydraulic design is based on a minimum flow of 230 L/min from the eight most remote in-rack sprinklers; up to HHS3 quick response, 68 °C and a minimum of K115, up to HHS4 a minimum of K160 (preferred). The ceiling design is taken from Table 12: up to HHS3, 12 at 5.2 bar for K200, 12 at 3.6 bar for K240, 12 at 2.8 bar for K320 and 12 at 2.8 bar for K360; for HHS4, 12 at 4.1 bar with K360.
• 6.6.2.2 (EN p. 44-47): modular ESFR in-rack design. ESFR sprinklers are used modularly inside the racks; the height of the warehouse is not limited; the scheme applies from HHS1-HHS5 and to open frame racks only. The water supply shall be able to deliver the in-rack design separately from the ceiling design, that is, the in-rack demand does not have to be added to the ceiling demand; the duration is at least 60 min. The number of in-rack sprinklers is read from Table 13 and the minimum required flow from the most remote in-rack sprinklers from Table 14 (for a 9.1 m vertical installation, K200 and 250 L/min up to HHS3; K200 and 380 L/min up to HHS4; K320 and 455 L/min up to HHS5; for a 12.2 m vertical installation, K320 and 455 L/min up to HHS3).

Unheated areas

Clause 6.5 (EN p. 35): there is no dry installation option for this ESFR concept; where dry pendent ESFR sprinklers are used, the installation is considered a wet installation. Designs with propylene glycol are permitted provided that the k-factor is not less than 320, that the premixed antifreeze solution does not exceed 30 % glycol by volume and is manufactured specifically for sprinkler systems, and that tree type pipework is used. In the same K320 and larger systems, the glycol concentration may be raised to 40 % by volume if it can be demonstrated that water reaches a sprinkler within 60 s; after 60 s no more than 5 % glycol by volume may be present. The hydraulic calculation of the demand is based on a wet installation.

Frequently Asked Questions

What is the shape of the ESFR design area?

EN 12845-2:2024 Table 6 (EN p. 34) gives the shape of the design area as sprinklers x range pipe. For a 12 sprinkler design the shape is 4 x 3, that is 4 sprinklers per range pipe on 3 range pipes. The shapes given are 3 x 3 for 9 sprinklers, 5 x 3 for 15 sprinklers, 5 x 4 for 20 sprinklers, 6 x 4 for 24 sprinklers and 7 x 4 + 2 x 1 for 30 sprinklers. Clause 6.6.1.2 (EN p. 38) also states that the 9 sprinkler design area is 3 sprinklers on each of 3 adjacent range pipes and the 10 sprinkler design is 3 sprinklers on each of 3 adjacent range pipes plus 1 sprinkler on a further range pipe.

What is the minimum ESFR design area in square metres?

Clause 6.6.1.2 (EN p. 38): the minimum design area (number of sprinklers x spacing) shall be 71 m², the exception being where the obstructed construction requires a sprinkler in every channel. The upper bound follows from the maximum area per sprinkler: since Clause 5.1.3.2 allows at most 9.3 m² per ESFR sprinkler, a 12 sprinkler design gives at most 111.6 m².

How is the ESFR water demand calculated?

TS EN 12845+A2:2026 Clause 14.3 (EN p. 104-105): Q = K x square root of P, with Q in litres per minute and P in bar. The k-factor and the minimum operating pressure are read from Table 7, the flow per sprinkler is found with this formula, it is multiplied by the number of sprinklers in the design and converted into a volume using the duration of supply in Table 6. Example: for HHS1-HHS3 at a ceiling of 13.7 m with K360, Table 7 gives a minimum of 2.8 bar; the flow per sprinkler is 360 x square root of 2.8, about 602 L/min, about 7 229 L/min for 12 sprinklers and about 434 m³ for 60 minutes.

Which commodity classification is used for ESFR?

EN 12845-2:2024 Annex A (normative, EN p. 59) is used; the classes are HHS1-HHS5 for storage and FH1-FH5 for non storage occupancies. Annex A also gives the conversion table from the EN 12845:2015 classes (Table A.1) and the classification flow chart for storage commodities containing plastics (Figure A.1). Annex C of EN 12845 is the alphabetical list of stored products with their categories (Category I-IV) and serves the HHS1-HHS4 classification of EN 12845 itself.

Is K280 an ESFR k-factor?

No. The ESFR column of Table 2 (EN p. 10) contains K200, K240, K320, K360, K400 and K480. K280 appears only in the CMSA columns and is not found in the ESFR design tables (Table 7, Table 10, Table 11).

What is the difference between Table 7 and Tables 10 and 11?

Table 7 (EN p. 36) is the general design table and is generally based on 12 heads; for that table Clause 6.6.1.1 states that Clause 5.2.6.1 (horizontal air flow) and Clause 5.3.3.2.2 (obstructions above racks) do not apply. Tables 10 and 11 (EN p. 41) apply together with the additional special requirements of Clause 6.6.1.2: 5.2.6.1 always applies, for obstructions above racks the recommended approach of 5.3.3.2.2 is applied, and the ceiling is non-combustible and preferably unobstructed. In these tables the design number of sprinklers is given together with the pressure as 9, 10, 12, 15 or 20.

References

• EN 12845-2:2024 Clause 4 (EN p. 6)
• EN 12845-2:2024 Clause 5.1.3.2, 5.1.3.5.2, Table 2 (EN p. 8-10)
• EN 12845-2:2024 Clause 5.2.1, 5.2.2, 5.1.3.7 (EN p. 12); 5.2.3 (EN p. 13); 5.2.4 (EN p. 16); 5.2.6.1 (EN p. 18); 5.2.6.2, 5.2.7 (EN p. 20)
• EN 12845-2:2024 Clause 6.1, 6.2 (EN p. 33)
• EN 12845-2:2024 Clause 6.4, Table 6 (EN p. 34)
• EN 12845-2:2024 Clause 6.5, 6.6.1.1 (EN p. 35)
• EN 12845-2:2024 Table 7 (EN p. 36)
• EN 12845-2:2024 Clause 6.6.1.2 (EN p. 38)
• EN 12845-2:2024 Table 10, Table 11 (EN p. 41)
• EN 12845-2:2024 Clause 6.6.2.1.1, Table 12 (EN p. 42-43)
• EN 12845-2:2024 Clause 6.6.2.2, Table 13, Table 14 (EN p. 44-47)
• EN 12845-2:2024 Annex A, Table A.1, Figure A.1 (EN p. 59-60)
• TS EN 12845+A2:2026 Clause 13.4.2 (EN p. 99), Clause 14.3 (EN p. 104-105)

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