Source: EN 12845-2:2024 Introduction (EN p. 4), Clause 4 (EN p. 6), Clause 5.1.1 (EN p. 7), Clauses 6.4 and 6.6 (EN p. 34-41), with TS EN 12845+A2:2026 Clause 14.3 (EN p. 104-105).
Three modes, three definitions
The Introduction of the standard defines three protection concepts:
- ESFR (early suppression fast response): operates in suppression mode with sprinklers conforming to EN 12259-13; it has the ability to significantly reduce the heat release rate of fires in storage risks. It is typically used in high hazard storage scenarios to provide effective protection with ceiling protection only (ESFR schemes using in-rack heads also exist). The designs are typically defined by k-factor, number of operating heads and required head pressure.
- CMSA (control mode specific application): operates in control mode, limiting the heat release rate of the fire. The designs are defined by the number of operating heads and the required head pressure.
- CMDA (control mode density area): operates in control mode in accordance with EN 12845-1, typically with sprinklers conforming to EN 12259-1. The designs are defined by a minimum water application rate (density, mm/min) to be applied over a given area of operation.
The Introduction also stresses this: ESFR and CMSA designs are less robust in dealing with adverse design features and non conformities; deviations from this standard carry a high risk of leading to total system failure.
Clauses 4 and 5.1.1: the basic restrictions
- Clause 4 (EN p. 6): ESFR sprinklers are used only in wet installations. CMSA sprinklers may be used in wet and dry installations. Open-top containers shall not be used in storage hazards protected by ESFR or CMSA unless specifically permitted in the standard.
- Clause 5.1.1 (EN p. 7): ESFR pendent, dry pendent or upright sprinklers conform to EN 12259-13. CMSA pendent, dry pendent or upright sprinklers conform to prEN 12259-15; in dry CMSA systems only dry pendent and upright sprinklers are used.
- NOTE 2 (EN p. 8): ESFR sprinklers typically have a nominal operating temperature of 68 °C to 74 °C and are fast response. CMSA sprinklers are also typically 68 °C to 74 °C; in dry systems generally 141 °C.
The text of the standard gives no numerical RTI band and no sprinkler orifice diameter for ESFR; those values belong to the product standards.
The k-factor family
Table 2 (EN p. 10) shows the k-factors used for ESFR and CMSA. The ESFR column contains K200, K240, K320, K360, K400 and K480; Table 7 (EN p. 36) gives the design criteria for these k-factors. The CMSA columns contain K160, K240, K280 and K360. K280 is not an ESFR k-factor; it does not appear in the ESFR design tables.
The flow formula is on the EN 12845 side. Clause 14.3 (EN p. 104-105):
Q = K √P
Q: flow in litres per minute; K: the constant given in the tables; P: the pressure in bar.
The definition of the K-factor in the terms list of the standard is the same: "the discharge coefficient in the formula Q = K√p; Q in litres per minute, p in bar" (EN p. 18).
Using this formula, the flows per sprinkler calculated from some cells of Table 7 (arithmetic, derived from the standard's values):
| Table 7 cell | Pressure | Calculated flow (L/min) |
|---|---|---|
| HHS1-HHS3, ceiling 7.6 m, K360 | 1.0 bar | 360 |
| HHS1-HHS3, ceiling 7.6 m, K320 | 1.7 bar | ≈ 417 |
| HHS1-HHS3, ceiling 7.6 m, K240 | 2.4 bar | ≈ 372 |
| HHS1-HHS3, ceiling 7.6 m, K200 | 3.4 bar | ≈ 369 |
| HHS1-HHS3, ceiling 15.2 m, K400 | 2.8 bar | ≈ 669 |
| HHS1-HHS3, ceiling 15.2 m, K480 | 3.8 bar | ≈ 936 |
The engineering reading here is this: within the same row, as the k-factor grows the required pressure falls and the flow per sprinkler stays almost the same. A large k-factor is the way to deliver the same quantity of water at a lower pressure and in coarser droplets.
Table 7: minimum operating pressures for ESFR ceiling only protection
The table below is the pendent columns of Table 7 of EN 12845-2:2024 (EN p. 36); the values are minimum operating pressures in bar and apply to designs of at least 12 ESFR sprinklers.
| Commodity class | Maximum ceiling/roof height (m) | Maximum storage height (m) | K200 | K240 | K320 | K360 | K400 | K480 |
|---|---|---|---|---|---|---|---|---|
| HHS1-HHS3 | 7.6 | 6.1 | 3.4 | 2.4 | 1.7 | 1.0 | - | - |
| HHS1-HHS3 | 9.1 | 7.6 | 3.4 | 2.4 | 1.7 | 1.0 | - | - |
| HHS1-HHS3 | 10.7 | 9.1 | 5.2 | 3.6 | 2.4 | 1.4 | - | - |
| HHS1-HHS3 | 12.2 | 10.7 | - | 3.6 | 2.8 | 1.7 | - | - |
| HHS1-HHS3 | 13.7 | 12.2 | - | - | 2.8 | 2.8 | - | - |
| HHS1-HHS3 | 15.2 | 13.3 | - | - | - | - | 2.8 | 3.8 |
| HHS1-HHS3 | 16.8 | 14.9 | - | - | - | - | 5.5 | 3.8 |
| HHS4 | 7.6 | 6.1 | 3.4 | 2.4 | 5.2 | 4.1 | - | - |
| HHS4 | 9.1 | 7.6 | 3.4 | 2.4 | 5.2 | 4.1 | - | - |
| HHS4 | 10.7 | 9.1 | - | - | 5.2 | 4.1 | - | - |
| HHS4 | 12.2 | 10.7 | - | - | 5.2 | 4.1 | - | - |
| HHS5 | 9.1 | 7.6 | - | - | - | 2.0 | - | - |
| HHS5 | 12.2 | 10.7 | - | - | - | 4.1 | - | - |
The footnotes to the table include the minimum aisle width (1.8 m or 2.4 m) for the 15.2 m and 16.8 m rows and the additional requirements specific to exposed expanded plastics for the HHS5 rows. There are also upright orientation columns for K200 and K240 (3.4 and 2.4 bar at ceilings of 7.6 and 9.1 m; 5.2 and 3.6 bar at a ceiling of 10.7 m).
Two lessons follow from the figures. First, in the HHS4 rows (the more demanding commodity class) the K320 and K360 pressures rise, they do not fall; in other words the choice of k-factor cannot be made independently of the commodity class. Second, at the same ceiling height some k-factors cannot be used at all; for the cells with a dash the rule of Clause 6.1 applies: interpolation and extrapolation are not permitted.
Duration of supply and the shape of the design area
Table 6 (Clause 6.4, EN p. 34):
| Number of ceiling sprinklers in the design | Duration of supply (min) | Shape of design area (sprinklers x range pipe) |
|---|---|---|
| 9 | 60 | 3 × 3 |
| 10 | 60 | 3 × 2 + 4 × 1 |
| 12 | 60 | 4 × 3 |
| 15 | 90 | 5 × 3 |
| 16 | 90 | 5 × 3 + 1 × 1 |
| 20 | 120 | 5 × 4 |
| 24 | 120 | 6 × 4 |
| 25 | 120 | 6 × 4 + 1 × 1 |
| 30 | 120 | 7 × 4 + 2 × 1 |
NOTE 2 and NOTE 3: with CMSA the duration is 120 min for roll paper storage and 180 min for rubber tyre storage, independently of the number of sprinklers.
Clause 6.6.1.1 (EN p. 35) states that the designs of Table 7 are generally based on 12 heads; Clause 6.6.1.2 (EN p. 38) requires the minimum design area (number of sprinklers × spacing) to be 71 m² (except where the obstructed construction requires a sprinkler in every channel).
Worked example (arithmetic from the standard's values): HHS1-HHS3, ceiling 9.1 m, K200 pendent, 3.4 bar. Per sprinkler, Q = 200 × √3.4 ≈ 369 L/min. For 12 sprinklers the total is ≈ 4 428 L/min. Since Table 6 gives 60 min for a 12 sprinkler design, the required volume of water is ≈ 265 700 L, that is about 266 m³. Had K360 been chosen in the same row (1.0 bar), the total would be 12 × 360 = 4 320 L/min and ≈ 259 m³ for 60 min.
Class conversion
EN 12845-2 uses the commodity classes HHS1-HHS5 (storage) and FH1-FH5 (non storage). Annex A (normative, EN p. 59) gives the conversion from the EN 12845:2015 classes: LH and OH1 to FH1; OH2 and OH3 to FH2; OH4 to FH3; HHP1 and HHP2 to FH4; HHP3 to FH5. Clause 6.2 (EN p. 33) states that ESFR and CMSA protection shall not be applied to FH3, FH4 and FH5 occupancies.
On the EN 12845 side the link is through Annex N and Annex P: for CMSA sprinkler systems (Annex N, EN p. 162) and for ESFR sprinkler systems (Annex P, EN p. 164), EN 12845-2 is applied together with that document. Annex P also recommends the use of three pump sets of 50 % capacity conforming to EN 17451 for the water supply of ESFR systems.
Frequently Asked Questions
Does ESFR really require high pressure?
No, there is no single pressure band. EN 12845-2:2024 Table 7 (EN p. 36) gives minimum operating pressures between 1.0 bar and 5.5 bar. For example, in class HHS1-HHS3 at a ceiling height of 7.6 m the values are 1.0 bar for K360, 1.7 bar for K320, 2.4 bar for K240 and 3.4 bar for K200. In the same table, 5.5 bar appears for K400 at a ceiling of 16.8 m. The pressure is read from the intersection of the k-factor with the ceiling and storage heights; there is no fixed lower limit.
Which k-factors does ESFR use?
The ESFR column of Table 2 (EN p. 10) contains K200, K240, K320, K360, K400 and K480; Table 7 (EN p. 36) gives the ESFR design criteria for these k-factors. K280 is a CMSA k-factor; the CMSA columns of Table 2 contain K160, K240, K280 and K360, and K280 does not appear in the ESFR design tables.
How is the ESFR flow calculated?
TS EN 12845+A2:2026 Clause 14.3 (EN p. 104-105): Q = K x square root of P, where Q is in litres per minute, K is the constant given in the tables and P is the pressure in bar. The definition of the K-factor in the terms list of the standard is the same: the discharge coefficient in the formula Q = K x square root of p, with Q in litres per minute and p in bar. For example, a K360 sprinkler delivers 360 L/min at 1.0 bar and a K200 sprinkler delivers about 369 L/min at 3.4 bar.
On how many sprinklers is an ESFR design based?
Clause 6.6.1.1 (EN p. 35): the designs in Table 7 are generally based on the operation of 12 sprinklers. Table 6 (EN p. 34) gives the duration of supply and the shape of the design area by number of sprinklers: 9 sprinklers 60 min and 3 x 3; 10 sprinklers 60 min; 12 sprinklers 60 min and 4 x 3; 15 and 16 sprinklers 90 min; 20, 24, 25 and 30 sprinklers 120 min. Clause 6.6.1.2 (EN p. 38) requires a minimum design area of 71 m².
What is the operating temperature and response type of an ESFR sprinkler?
Clause 5.1.1 NOTE 2 (EN p. 8): ESFR sprinklers typically have a nominal operating temperature of 68 °C to 74 °C and are fast response. CMSA sprinklers are also typically 68 °C to 74 °C; in dry systems a nominal operating temperature of 141 °C is generally used. No numerical RTI band for ESFR is given in the text of the standard.
What is the difference between ESFR, CMSA and CMDA?
EN 12845-2:2024 Introduction (EN p. 4): ESFR operates in suppression mode with sprinklers conforming to EN 12259-13, that is, it has the ability to significantly reduce the heat release rate of fires in storage risks; the designs are typically defined by k-factor, number of operating heads and required head pressure. CMSA operates in control mode and its designs are defined by the number of operating heads and the required head pressure. CMDA operates in control mode in accordance with EN 12845-1 and its designs are defined by a minimum water application rate (density, mm/min) over a given area of operation.
References
- EN 12845-2:2024 Introduction (EN p. 4)
- EN 12845-2:2024 Clause 4 (EN p. 6)
- EN 12845-2:2024 Clause 5.1.1 (EN p. 7) and NOTE 2 (EN p. 8)
- EN 12845-2:2024 Table 2 (EN p. 10)
- 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 6.6.1.1 (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 Annex A, Table A.1 (EN p. 59)
- TS EN 12845+A2:2026 Clause 3 definition of K-factor (EN p. 18)
- TS EN 12845+A2:2026 Clause 14.3 (EN p. 104-105)
- TS EN 12845+A2:2026 Annex N (EN p. 162), Annex P (EN p. 164)
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Download MEP Calc on the App StoreTS EN 12845+A2:2026 (EN 12845:2015+A2:2026) Fixed firefighting systems — Automatic sprinkler systems — Design, installation and maintenance; TS EN 12845-2:2025 (EN 12845-2:2024) ESFR and CMSA sprinkler systems. Every figure in this article is taken from the published standard text; clause, table and page references are listed under References. General information only, not a substitute for the standard or for a design review.