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 an intermediate temperature rating of 79–107 °C is preferred. Minimum operating pressures and design sprinkler counts for K200 to K480 by ceiling height:

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 the first four heads open must not exceed 40 seconds (20 seconds in certain special cases). The operating sprinkler count increases on dry systems:

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.
• CMSA: minimum spacing 2.4 m; maximum 3.7 m, reducing to 3.1 m under obstructed combustible ceilings. Maximum coverage 12 m² under standard roofs or 9.3 m² otherwise, minimum 7.5 m².
• CMDA: maximum coverage 21 m² in LH, 12 m² in OH and 9 m² in HHP and HHS. Minimum spacing 2 m.

5.2 Ceiling and roof slope

For ESFR and CMSA the maximum slope is 10 degrees. If exceeded, the options are: (1) a fire-resisting suspended ceiling with separate sprinklers above and below, (2) in-rack sprinklers with barriers only, or (3) converting the design to CMDA.

5.3 Deflector distance below the ceiling

• ESFR pendent (K200–K240): 160–325 mm.
• ESFR pendent (K320–K480): 160–425 mm.
• CMSA upright: 100–325 mm under an unobstructed ceiling; 25–150 mm below the underside of the obstruction where the ceiling is obstructed.

5.4 Air velocity at ceiling level

Horizontal or vertical air velocity at ceiling level must not exceed 1.5 m/s, otherwise sprinklers remote from the fire can open and the hydraulic design collapses. If it is exceeded, the options are automatic fan and damper shutdown on detection, a flame detector within a 3.0 m radius of the affected head, or a 30% increase in the design area on a wet system.

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, an additional sprinkler of the same characteristics as the ceiling sprinklers is installed beneath it and fed by pipe of the same diameter. To preserve the umbrella pattern, an obstruction 150 mm below the deflector must be at least 700 mm away horizontally, and one 300 mm below at least 1000 mm away.

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. 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). HHP1 is 7.5, HHP2 is 10.0 and HHP3 is 12.5 mm/min, over 260 wet or 325 dry. HHP4 requires a deluge system. On dry and alternate systems the HHS ceiling operating area is increased by 25%.

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

ESFR may only be used on wet pipe systems; there is 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 heads rated 79 to 107 degrees C are preferred. At the maximum ceiling of 16.8 m the protection is K480 with 9 sprinklers at 3.8 bar.

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 the first four heads open must not exceed 40 seconds, reduced to 20 seconds in certain special designs. To compensate for the delayed discharge the operating sprinkler count is increased - for example a K240 upright requires 15 heads wet and 24 to 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 ceilings, with maximum coverage 12 square metres under standard roofs. 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. If exceeded you need either a fire-resisting suspended ceiling with sprinklers above and below, in-rack sprinklers with barriers, or a conversion to CMDA. Air velocity at ceiling level must not exceed 1.5 m/s; if it does, fans and dampers must shut down automatically on detection, a flame detector must be installed within 3.0 m of the affected head, or the design area must be increased by 30% on a wet system.

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