TS EN 12845 Sprinkler Design Criteria Guide: CMDA, ESFR and CMSA

This guide collects the hydraulic design and layout parameters of the three suppression concepts — CMDA, ESFR and CMSA — across all hazard classes, per TS EN 12845 (2015+A2:2026) and EN 12845-2:2024. All values are metric, so the tables can be used directly as a desk reference on site.

1. The Three Suppression Concepts

• CMDA (density/area): controls the fire; hydraulics are built from design density (mm/min) multiplied by area of operation (m²). Used in LH, OH and HHP.
• ESFR (early suppression): early suppression from ceiling level; designed from K-factor, sprinkler count and minimum operating pressure. Wet systems only.
• CMSA (specific application): control by large droplets; calculated from the operating sprinkler count and minimum end pressure. Wet or dry.

2. CMDA Design Criteria (LH, OH, HHP)

3. ESFR Design Criteria (Wet Only, Ceiling up to 16.8 m)

ESFR heads are fast response, typically 68–74 °C nominal; for HHS5 (exposed expanded plastics) intermediate temperature rated (79–107 °C) K360 pendent ESFR sprinklers are required (EN 12845-2 clause 5.4). Minimum operating pressures by ceiling height per EN 12845-2 Table 7 (ceiling-only, at least 12 sprinklers) and Table 8 (rubber tyres):

The 15.2 m and 16.8 m rows exclude multiple-row racks and require a minimum aisle width of 1.8 m (2.4 m for K400 at 16.8 m). For rubber tyres, K240 is listed only as an upright head at 2.4 bar. The designs with additional special requirements in Tables 10 and 11 (clause 6.6.1.2) can reduce the sprinkler count, for example K480 with 9 sprinklers at 3.8 bar for a 16.8 m ceiling and 15.2 m storage, or K400 with 10 sprinklers at 2.8 bar for a 15.2 m ceiling and 13.7 m storage.

4. CMSA Design Criteria (Wet/Dry — STC1 Block and STC4 Rack)

On dry CMSA systems the nominal temperature rating is usually 141 °C, and the water delivery time with four sprinklers operating must not exceed 40 seconds, or the time given in the design table (20, 25, 30 or 60 seconds) where it specifies one (clause 6.7.1). The operating sprinkler count increases on dry systems (EN 12845-2 Tables 15 to 20):

5. Installation, Layout and Physical Limits

5.1 Sprinkler spacing and coverage areas

• ESFR: minimum spacing 2.4 m; maximum 3.7 m for ceilings up to 9.1 m, or 3.1 m above that. Maximum 9.3 m² and minimum 6 m² per head. Distance to a wall may not exceed 50% of the maximum permitted spacing (EN 12845-2 clause 5.1.3.2).
• CMSA: minimum spacing 2.4 m; maximum 3.7 m, reducing to 3.1 m under obstructed combustible construction. Distance to a wall may not exceed 50% of the maximum spacing. Maximum coverage 12 m² for STC1 storage under any ceiling other than obstructed combustible construction, 9.3 m² in all other cases; minimum 7.5 m².
• CMDA: maximum coverage 21 m² in LH, 12 m² in OH and 9 m² in HHP and HHS (EN 12845 Table 19). Minimum spacing 2 m (clause 12.3).

5.2 Ceiling and roof slope

For ESFR and CMSA the maximum slope is 10 degrees (17.6%) (EN 12845-2 clause 5.2.1). If exceeded, the options are: (1) a flat, continuous, horizontal false ceiling over the affected area and two sprinkler lines beyond in all directions, meeting the strength requirement of clause 5.2.2, with sprinklers both above and below it, (2) for rack-only storage, in-rack sprinklers per clause 6.6.2.1 plus an additional in-rack level at the top of storage including face sprinklers, or (3) designing the system to EN 12845 (CMDA).

5.3 Deflector distance below the ceiling

• All: the deflector must be at least 100 mm below the ceiling (EN 12845-2 clause 5.1.3.5.2); the maximum distance of the thermal element below the ceiling comes from Table 2.
• ESFR (obstructed or unobstructed): maximum 325 mm for K200, K240 and K400; maximum 425 mm for K320, K360 and K480.
• CMSA: under an unobstructed ceiling maximum 225 mm for K160/K240 and 325 mm for K280/K360; under obstructed construction maximum 325 mm. Where the channel exemption is used, the deflector sits 25–150 mm below a non-combustible structural member (25–100 mm below a combustible one).

5.4 Air velocity at ceiling level

Air velocity at ceiling-level sprinklers must not exceed 1.5 m/s (EN 12845-2 clause 5.2.6), otherwise sprinklers remote from the fire can open and the hydraulic design no longer holds. For horizontal airflow that cannot be kept below this, flame detection at ceiling level (covering a 3.0 m radius around all affected sprinklers) or linear heat detection in the transverse flues at the top of the racks is installed, and in both cases the detection shuts down the airflow automatically. For vertical airflow the options also include shutdown on sprinkler waterflow alarm, a 30% increase in the design area on a wet system, a flat continuous false ceiling, or in-rack sprinklers at the flue intersections.

5.5 Effect of obstructions on the discharge pattern

Where a flat or solid obstruction such as a cable tray, duct or beam is wider than 0.6 m, additional sprinklers of the same type as the ceiling sprinklers are installed beneath it and fed by pipe of the same size as the ceiling-level branch line (EN 12845-2 clause 5.3.3.2.4). To preserve the umbrella pattern, a ceiling object extending 150 mm below the deflector must be at least 700 mm away horizontally, and one extending 300 mm below at least 1000 mm away (Table 3).

Frequently Asked Questions

What is the fundamental design difference between CMDA, ESFR and CMSA?

CMDA controls the fire and its hydraulics are built from design density in mm/min multiplied by the area of operation, used in LH, OH and HHP classes. ESFR achieves early suppression from ceiling level and is designed from K-factor, sprinkler count and minimum operating pressure, on wet systems only. CMSA achieves control through large droplets and is calculated from the operating sprinkler count and minimum end pressure, on either wet or dry systems.

What are the EN 12845 CMDA design densities and operating areas?

LH is 2.25 mm/min over 84 square metres, with no dry option (use OH1). OH1 to OH4 all use 5.0 mm/min, with wet areas of 72, 144, 216 and 360 square metres and dry areas of 90, 180 and 270 (OH4 has no dry option; use HHP1). HHP1 is 7.5, HHP2 is 10.0 and HHP3 is 12.5 mm/min, over 260 wet or 325 dry. HHP4 needs special consideration; deluge systems are outside the scope of EN 12845. Dry and alternate systems should be avoided for HHS; if used, the ceiling operating area should be increased by 25%.

Can ESFR be used on dry systems, and what temperature ratings apply?

ESFR may only be used on wet pipe systems; EN 12845-2 has no dry option. The heads are fast response with a nominal temperature typically between 68 and 74 degrees C. For HHS5, which covers exposed expanded plastics, intermediate temperature rated (79 to 107 degrees C) K360 pendent ESFR sprinklers are required. At the maximum ceiling of 16.8 m (storage up to 14.9 m) Table 7 requires K480 with 12 sprinklers at 3.8 bar; with the additional special requirements of Table 11 this can drop to 9 sprinklers at 3.8 bar with 15.2 m storage.

What water delivery time applies to a dry CMSA system?

CMSA can be installed wet or dry. On a dry system the nominal head temperature is usually 141 degrees C, and the water delivery time with four sprinklers operating must not exceed 40 seconds, or the time given in the design table (20, 25, 30 or 60 seconds) where it specifies one. To compensate for the delayed discharge the operating sprinkler count is increased - for example a K240 upright over STC1 block storage requires 15 heads wet and 25 dry.

What are the sprinkler spacing and coverage limits in EN 12845?

For ESFR, minimum spacing is 2.4 m and maximum is 3.7 m for ceilings up to 9.1 m or 3.1 m above that, with maximum 9.3 and minimum 6 square metres per head. For CMSA, minimum 2.4 m and maximum 3.7 m, reducing to 3.1 m under obstructed combustible construction, with maximum coverage 12 square metres for STC1 storage (except under obstructed combustible construction), 9.3 otherwise and minimum 7.5. For CMDA, maximum coverage is 21 square metres in LH, 12 in OH and 9 in HHP and HHS, with a 2 m minimum spacing.

What are the ceiling slope and air velocity limits for ESFR and CMSA?

The maximum ceiling slope is 10 degrees (17.6%). If exceeded you need either a flat, continuous horizontal false ceiling with sprinklers above and below it, in-rack sprinklers plus an additional in-rack level at the top of storage for rack-only storage, or a design to EN 12845 (CMDA). Air velocity at ceiling-level sprinklers must not exceed 1.5 m/s. For horizontal airflow that exceeds it, flame detection at ceiling level (3.0 m radius) or linear heat detection in the racks must shut down the airflow automatically; for vertical airflow a 30% increase in the design area on a wet system is also among the options.

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