Question 1

What is the difference between CMDA, CMSA and ESFR?

Accepted Answer

CMDA (Control Mode Density Area) is the classic EN 12845-1 approach: a density times area formula, aimed at control, with a low K-factor. CMSA (Control Mode Specific Application) uses large droplets, is product specific and has a medium K-factor. ESFR (Early Suppression Fast Response) aims at suppression, with a high K-factor and fast RTI. The three modes were developed on different philosophies for different fire scenarios.

Question 2

When is each selected?

Accepted Answer

Stack up to 4 m, light or ordinary hazard: CMDA. Stack of 4 to 7 m or a specific commodity (rubber, paper): CMSA. Stack of 6 m or more in a high-bay warehouse with a suitable ceiling: ESFR. Ceiling slope above 5 percent or large skylights: CMSA. Fastest control of the fire load: ESFR. Limited water supply: ESFR (only 12 sprinklers).

Question 3

What is EN 12845-2?

Accepted Answer

EN 12845-2:2024 is the new European standard for ESFR and CMSA sprinkler systems. EN 12845-1 keeps the traditional CMDA (Control Mode Density Area) design; Part 2 takes the high-response modern technologies (ESFR and CMSA) into a separate standard, published in 2024.

Question 4

What is the definition of a high-rise?

Accepted Answer

The high-rise annex gives no exact metre threshold, but in practice it is a building where the pressure difference between the highest and lowest sprinkler exceeds 4 bar, or a height the fire service ladder cannot reach (BYKHY calls above 21.5 m a high building in Turkey). Mostly seven storeys and above.

Question 5

What does effective capacity mean?

Accepted Answer

Effective capacity is the usable volume between the normal water level (N) and the low water level (X). Water below the suction pipe does not count, because it cannot be delivered to the pump.

Question 6

What does an anti-vortex plate achieve?

Accepted Answer

A vortex inhibitor breaks the vortex forming at the suction pipe inlet and prevents air entrainment. With a plate fitted, the A distance between the suction pipe and the low water level can drop to 0.10 m; without one, a 100 mm pipe needs 0.37 m.

Question 7

Why can a sprinkler pump not be started star-delta?

Accepted Answer

EN 12845 requires the pump to be running at rated capacity within 15 seconds of the start signal. The current and torque dip during the star-delta transition can push the pump into a stall region while there is load at the valve manifold. Direct-on-line starting is both the fastest starting method and the arrangement with the fewest failure points, on single-relay, single-contactor logic. Soft starters and VFDs are not preferred in practice either; listed sprinkler controllers come with DOL logic as standard.

Question 8

Why is no overload relay used on the pump motor?

Accepted Answer

The clause requires only a high rupturing capacity (HRC) fuse in the controller, carrying the starting current for at least 20 seconds. The overcurrent protection is against short circuit only; there is NO overload protection. The reason: during a fire, the motor must keep turning even if it exceeds its thermal limit. An overload relay fitted to "save the pump" opens the circuit during a fire and the system collapses. Burning the motor is better than putting the sprinklers into a coma.

Question 9

What is the minimum suction pipe diameter?

Accepted Answer

At least DN65 on a positive head installation, with the velocity not exceeding 1.8 m/s; and at least DN80 on a suction lift installation, with the velocity not exceeding 1.5 m/s. In every case the diameter must not be smaller than the pump flange.

Question 10

Which clause defines equivalent length?

Accepted Answer

Friction loss for valves and fittings is calculated by the equivalent length method. The values come from the fittings table; where a manufacturer's value exists, it takes priority. The table is given for C=120 steel pipe and is converted for other C values with a multiplier.

Question 11

What is the difference between HHP and HHS?

Accepted Answer

HHP (High Hazard Process) covers manufacturing and processing: paint shops, plastics moulding, rubber, timber working. HHS (High Hazard Storage) covers storage. Densities for HHP come from one table; HHS is designed from a different table with a different calculation logic.

Question 12

What is the difference between HHS and HHP?

Accepted Answer

HHP covers production and process areas; HHS covers storage areas on pallets, racking or in block stacks. The HHS density varies between 7.5 and 30 mm/min depending on the material category and height, while HHP is fixed by table (7.5, 10.0 or 12.5 mm/min over 260 m2).

Question 13

How many in-rack sprinklers are assumed to operate in the hydraulic calculation?

Accepted Answer

3 sprinklers at each level, over a maximum of 3 levels together - so at most 9 in-rack sprinklers. Depending on the aisle width, 1, 2 or 3 racks are included hydraulically.

Question 14

Which buildings fall into the LH class?

Accepted Answer

Spaces with a low fire load and low combustibility, no single compartment exceeding 126 m2, and at least 30 minutes' fire resistance. The occupancy annex lists exactly: schools (specified areas), offices (specified areas) and prisons. Hospitals, hotels and libraries are listed as OH-1; LH is not assumed for them.

Question 15

What is the minimum sprinkler discharge pressure in EN 12845?

Accepted Answer

Measured at the most unfavourable sprinkler: 0.7 bar for LH, 0.35 bar for OH, and 0.5 bar for HHP and HHS excluding in-rack. For K115 in-rack, 1.0 bar; for K80 in-rack, 2.0 bar.

Question 16

Why must the area of operation be rectangular?

Accepted Answer

The standard requires the area at the hydraulically most unfavourable position to be as rectangular as practicable and symmetrical with the sprinkler layout. The aim is to imitate the circular or square spread of a real fire. If a long, narrow strip is chosen, the same number of sprinklers is spread along one line, the friction losses fall unrealistically and the pump pressure comes out short.

Question 17

What is the minimum distance between two sprinklers?

Accepted Answer

2.0 m. Smaller values such as 1.5 m are permitted only where a 200 mm by 150 mm baffle is fitted, for in-rack intermediate level sprinklers, or for walkway and lift shaft applications.

Question 18

What is cold soldering?

Accepted Answer

Cold soldering is where the first sprinkler to operate cools the hot smoke layer and prevents adjacent sprinklers reaching their operating temperature. Where sprinklers are closer than 2 m, the neighbour is drenched, its solder stays cold and it never opens. The result: the fire spreads outside the design area.

Question 19

How large an area can one sprinkler protect?

Accepted Answer

For ceiling, upright and pendent sprinklers the maximum is 21.0 m2 for LH, 12.0 m2 for OH and 9.0 m2 for HHP and HHS.

Question 20

How is the sprinkler temperature rating selected under EN 12845?

Accepted Answer

The rating selected must be at least 30 degrees C above the highest anticipated ambient temperature, but not raised further than necessary. In a temperate climate the typical recommendation is 68 or 74 degrees C; under unventilated concealed ceiling voids, skylights and glazed roofs, 93 or 100 degrees C may be needed. Near ovens, dryers and heaters, additional assessment is essential.

Question 21

What is RTI and what are its units?

Accepted Answer

RTI (Response Time Index) is the parameter describing the delay with which a liquid-filled glass bulb or a fusible link senses heat. Its unit is (m.s)^0.5, the square root of metre-seconds. A low RTI means fast response, a high RTI slow response.

Question 22

Why is a 90 minute tank required for high hazard storage?

Accepted Answer

The standard recognises that the fire load and growth rate in high hazard storage are far higher than in OH. With conventional sprinklers rather than ESFR or CMSA, a minimum of 90 minutes of uninterrupted flow is required until the fire service intervention is complete. A 30 minute tank is non-standard for a logistics warehouse and grounds for direct rejection at a compliance inspection.

Question 23

What is the area of operation?

Accepted Answer

The area of operation is the largest area assumed to have simultaneous sprinkler activation in the hydraulic calculation. It is shaped rectangular on a wet system and square on a dry or alternate system, and placed at the hydraulically most unfavourable position.

Question 24

What is suppression and how does it differ from control?

Accepted Answer

Control (CMDA) prevents the fire spreading by wetting the surrounding area, buying time for the fire service. Suppression (ESFR) extinguishes the fire - it strikes the flame head directly, achieving suppression within 60 to 90 seconds of sprinkler activation. ESFR has a high water demand but finishes in minutes, while CMDA runs for hours.

Question 25

What is the 12 sprinkler rule?

Accepted Answer

The ESFR design area is 4 rows of 3 sprinklers, that is 12 sprinklers. It is the worst-case fire scenario: 12 sprinklers activate at the centre of the fire and suppress it. All 12 are calculated at the most remote and highest position, and each must receive the minimum pressure. Protection outside that design area is not counted; it is sufficient that 12 sprinklers suffice at the real fire area.

Question 26

Can CPVC sprinkler pipe be used anywhere?

Accepted Answer

No. FM DS 2-0 permits it only in HC-1 (light fire load) areas below 65 degrees C. It is accepted for wet pipe systems and prohibited for dry pipe and higher hazards.

Question 27

What is MIC and how do I recognise it?

Accepted Answer

MIC is microbiologically influenced corrosion. Tubercles (nodular deposits) on the internal pipe surface, pitting (pinhole-like porosity) and a hydrogen sulphide smell (rotten eggs) are typical indicators. It is confirmed by endoscopic inspection plus detection of iron-oxidising bacteria (Gallionella) in a water quality test.

Question 28

Is sway bracing required for DN50 pipe and below?

Accepted Answer

Under FM DS 2-8, pipe of DN50 and below does not require sway bracing. Seismic-rated hangers (seismic rod and U-bolt types) are still mandatory. The full lateral plus longitudinal brace package applies from DN65 upwards.

Question 29

C=100 or C=120 for a wet pipe sprinkler system?

Accepted Answer

FM takes C=100 as the conservative choice. NFPA 13 permits C=120 for a new system, but the field assumption for wet pipe over 20 years and more is C=100. C=100 is always recommended for low-risk design, because it guarantees real performance.

Question 30

How is fire water tank capacity calculated?

Accepted Answer

Design flow (sprinklers plus standpipe plus hose) times the design duration. HC-1 30 min, HC-2 60 min, HC-3 90 to 120 min, storage 60 to 180 min. The hose stream allowance of 950 to 3800 L/min times the duration is added. Example: 5500 L/min x 60 min plus 950 L/min x 60 min = 387 m3.

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