A sprinkler water supply has three independent qualities: adequate flow and pressure (Clause 7), adequate duration (Clause 8.1.1) and uninterrupted availability (Clauses 8.1.2 and 8.1.3). This article collects the second and third of these, that is the provisions on duration, continuity and frost protection, from the standard's own text. Source: TS EN 12845+A2:2026, Clause 8.1, EN p.42 (TSE p.45).
1. Duration (Clause 8.1.1)
Clause 8.1.1 (EN p.42) first sets the general requirement: "Water supplies shall be capable of providing the required pressure/flow conditions of the system at least automatically." It then gives the durations. Where the water supply is also used for other fire fighting systems, reference is made to Clause 9.6.4; except in the cases specified for pressure tanks, each water supply shall have sufficient capacity for the following minimum durations:
| Hazard class | Minimum duration |
|---|---|
| LH | 30 minutes |
| OH | 60 minutes |
| HHP | 90 minutes |
| HHS | 90 minutes |
Source: Clause 8.1.1, EN p.42 (TSE p.45).
The NOTE to the clause introduces an important exemption: "For town mains, inexhaustible sources and all pre-calculated systems, the duration is implicit in the requirements given in this standard." In other words, in a pre-calculated system the volume from Table 9 or Table 10 already includes the duration; no further multiplication is made.
2. Water volume (Clause 9.3.2)
Fully calculated systems
Clause 9.3.2.3 (EN p.48) is a single sentence: "The minimum effective water volume shall be calculated by multiplying the maximum demand flow (Qmax) by the duration specified in 8.1.1."
V_min = Q_max x t
Here Q_max is the maximum demand flow from the hydraulic calculation and t is the duration from Clause 8.1.1. The standard adds no hose reel or fire brigade allowance to this formula; there is no provision in TS EN 12845+A2 adding a hose allowance to the sprinkler design flow.
Pre-calculated LH and OH systems: Table 9
The water volumes specified in Table 9 are reserved for the use of the sprinkler system only.
| Group | Height h of the highest sprinkler above the lowest sprinkler | Minimum water volume (m³) |
|---|---|---|
| LH (wet or pre-action) | h ≤ 15 m | 9 |
| LH (wet or pre-action) | 15 < h ≤ 30 m | 10 |
| LH (wet or pre-action) | 30 < h ≤ 45 m | 11 |
| OH1 wet or pre-action | h ≤ 15 m | 55 |
| OH1 wet or pre-action | 15 < h ≤ 30 m | 70 |
| OH1 wet or pre-action | 30 < h ≤ 45 m | 80 |
| OH1 dry/alternate; OH2 wet or pre-action | h ≤ 15 m | 105 |
| OH1 dry/alternate; OH2 wet or pre-action | 15 < h ≤ 30 m | 125 |
| OH1 dry/alternate; OH2 wet or pre-action | 30 < h ≤ 45 m | 140 |
| OH2 dry/alternate; OH3 wet or pre-action | h ≤ 15 m | 135 |
| OH2 dry/alternate; OH3 wet or pre-action | 15 < h ≤ 30 m | 160 |
| OH2 dry/alternate; OH3 wet or pre-action | 30 < h ≤ 45 m | 185 |
| OH3 dry/alternate; OH4 wet or pre-action | h ≤ 15 m | 160 |
| OH3 dry/alternate; OH4 wet or pre-action | 15 < h ≤ 30 m | 185 |
| OH3 dry/alternate; OH4 wet or pre-action | 30 < h ≤ 45 m | 200 |
| OH4 dry or alternate | - | Use HH protection |
Source: Table 9, Clause 9.3.2.2, EN p.47 (TSE p.50). NOTE: sprinklers in the sprinkler valve room are excluded.
Pre-calculated HHP and HHS systems: Table 10
| Design density not exceeded (mm/min) | Wet systems (m³) | Dry systems (m³) |
|---|---|---|
| 7.5 | 225 | 280 |
| 10.0 | 275 | 345 |
| 12.5 | 350 | 440 |
| 15.0 | 425 | 530 |
| 17.5 | 450 | 560 |
| 20.0 | 575 | 720 |
| 22.5 | 650 | 815 |
| 25.0 | 725 | 905 |
| 27.5 | 800 | 1 000 |
| 30.0 | 875 | 1 090 |
Source: Table 10, Clause 9.3.2.2, EN p.48 (TSE p.51).
For comparison: a design density of 12.5 mm/min corresponds, according to Table 7 (Clause 7.3.2.1, EN p.40), to a maximum demand flow of 3 800 l/min in a wet or pre-action system and 4 800 l/min in a dry or alternate system. With the 90 minute HHS duration, 3 800 x 90 = 342 000 litres = 342 m³; the value of 350 m³ in Table 10 remains above that.
Reduced capacity tank
Clause 9.3.2.1 (EN p.47) states that the minimum volume can be provided in two ways: a full capacity tank whose effective capacity is at least equal to the specified water capacity, or a reduced capacity tank in which the required water volume is provided jointly by the effective capacity of the tank plus an automatic infill (see Clause 9.3.4).
Clause 9.3.4 (EN p.48) sets five conditions for a reduced capacity tank:
- a) the inflow shall be from a town main and shall be automatic, through at least two mechanical ball valves. The inflow shall not adversely affect the pump set suction. The failure of a single ball valve shall not disturb the required infill rate;
- b) the effective capacity of the tank shall not be less than that shown in Table 11;
- c) the tank capacity plus the inflow rate shall be sufficient to supply the system at the full capacity specified in Clause 9.3.2;
- d) it shall be possible to check the inflow capacity;
- e) the inflow arrangement shall be accessible for inspection.
| Hazard class | Minimum effective capacity (m³) |
|---|---|
| LH (wet or pre-action) | 5 |
| OH1 wet or pre-action | 10 |
| OH1 dry/alternate; OH2 wet or pre-action | 20 |
| OH2 dry/alternate; OH3 wet or pre-action | 30 |
| OH3 dry/alternate; OH4 wet or pre-action | 50 |
| HHP and HHS | 70 (but in no case less than 10 % of the full capacity) |
Source: Table 11, Clause 9.3.4, EN p.49 (TSE p.52).
Infill rate
Clause 9.3.3 (EN p.48): for full capacity tanks the water supply shall be capable of refilling the tank in not more than 36 hours. The outlet of the supply pipe shall be at least 2.0 m horizontally from the inlet of the suction pipe.
3. Continuity (Clause 8.1.2)
Clause 8.1.2 (EN p.42) regulates the availability of the water supply:
- A water supply shall not be liable to be affected by possible frost conditions, drought, flooding or other conditions that could reduce the flow or the effective capacity, or render the supply inoperative.
- All possible steps shall be taken to ensure the continuity and reliability of the water supplies.
- Water supplies should preferably be under the control of the user; otherwise reliability and the right of use shall be guaranteed by the body holding the control.
- The water shall be free from fibrous or other suspended matter that could form deposits in the system pipework. Salt or brackish water shall not be retained in sprinkler installation pipework. Where no suitable source of fresh water is available, a salt or brackish source may be used provided that the installation is normally kept charged with fresh water.
In addition, Clause 8.4 (EN p.44) imposes a housing prohibition: water supply equipment such as pumps, pressure tanks and gravity tanks shall not be housed in buildings or parts of premises containing hazardous processes or explosion risks. Water supplies, stop valves and control valve sets are installed so that they can be reached safely even in the event of fire. All components are secured against interference and adequately protected against freezing.
Clause 9.7 (EN p.57) regulates the isolation of the supplies from each other: a problem or maintenance on one supply shall not disturb the operation of another supply.
4. Frost protection
Frost protection appears in four separate places in the standard.
a) Supply pipe and control valve
Clause 8.1.3 (EN p.42): "The supply pipe and the control valve set shall be maintained at a minimum temperature of 4 °C."
b) Equipment rooms
| Location | Minimum temperature | Source |
|---|---|---|
| Pressure tank and its housing | 4 °C | Clause 9.5.2, EN p.54 |
| Electric pump set compartment | 4 °C | Clause 10.3.3, EN p.58 |
| Diesel pump set compartment | 10 °C | Clause 10.3.3, EN p.58 |
Clause 9.5.2 also requires the pressure tank to be housed in one of three places: a sprinkler protected building; a separate, sprinkler protected building of Euroclass A1 or A2 construction (or the equivalent) used only to house fire protection water supplies and equipment; or an unprotected building located in a compartment with 60 minutes fire resistance and containing no combustible material. Where the pressure tank is housed in a sprinkler protected building, the area is enclosed by construction with a fire resistance of at least 30 minutes.
c) Storage tank
Clause 9.3.2.1 (EN p.47): "Where the tank is not frost resistant, the normal water level shall be raised by at least 1.0 m and ice venting shall be provided." Ready access shall be provided for closed tanks. Except for open reservoirs, tanks are fitted with a water level indicator readable from outside.
d) Pipework: three methods
Clause 11.1.2.1 (EN p.66): "Parts of the installation subject to freezing may be protected by antifreeze solution, by electrical trace heating or by subsidiary dry pipe or alternate extensions (see 11.5)."
Antifreeze solution (Clause 11.1.2.2, EN p.66):
- The number of sprinklers in any section of pipe protected by antifreeze solution shall not exceed 20.
- Where one control valve set controls more than two antifreeze sections, the total number of sprinklers in the antifreeze sections shall not exceed 100.
- The freezing point of the antifreeze solution shall be below the expected minimum temperature of the location.
- The specific gravity of the prepared solution shall be checked with a suitable hydrometer.
- Backflow prevention devices shall be fitted to systems relying on antifreeze solution in order to prevent contamination of the water.
Clause 11.1.2.2 does not specify the type of antifreeze; neither propylene glycol nor any other chemical is named.
Electrical trace heating (Clause 11.1.2.3, EN p.66-67):
- The trace heating system shall be monitored for failure of the power supply and for failure of the heating element(s) or sensor(s) (see Annex I).
- Euroclass A1 or A2 (or the equivalent) insulation shall be provided to the pipework.
- Duplicate heating elements shall be provided on the unheated pipework; each of the two elements shall be capable of maintaining the pipework at a minimum of 4 °C.
- Each trace heating circuit shall be electrically monitored and switched by separate circuits.
- The trace heating tape shall not cross over other trace heating tapes.
- The trace heating tape shall be fixed to the opposite side of the pipe from the sprinkler heads.
- The trace heating tape shall terminate within 25 mm of the pipe ends.
- All pipework with trace heating shall be insulated with Euroclass A1 or A2 (or the equivalent) insulating material at least 25 mm thick and with a waterproof covering. All ends shall be sealed to prevent the ingress of water.
- The maximum power of the trace heating tape shall be 10 W/m.
Subsidiary dry/alternate extension (Clause 11.5, EN p.69): installed as a dry or alternate extension to a wet installation in small areas liable to frost damage within an otherwise adequately heated building; or as a dry pipe extension to a wet or alternate installation in cold stores and in high temperature ovens or furnaces. The number of sprinklers per extension shall not exceed 100, and where more than two extensions are controlled by one control valve set, the total shall not exceed 250 (Clause 11.5.2).
The limit for the wet installation itself is in Clause 11.1.1 (EN p.66): wet pipe installations are installed only in locations where there is no possibility of frost damage to the installation and where the ambient temperature will not exceed 95 °C. Dry pipe installations are installed only in locations where there is a possibility of frost damage or where the temperature exceeds 70 °C (for example drying ovens) (Clause 11.2.1, EN p.67).
5. The counterparts on the maintenance side
| Interval | Activity | Source |
|---|---|---|
| Weekly | All water levels are checked and recorded: elevated private reservoirs, rivers, canals, lakes, water storage tanks (including pump priming water tanks and pressure tanks) | Clause 20.2.2.2 b, EN p.119 |
| Weekly | Heating systems that prevent freezing are checked for correct operation | Clause 20.2.2.6, EN p.120 |
| Annually | The ball valves in water storage tanks are checked for correct operation | Clause 20.3.4.4, EN p.122 |
| 3 yearly | All tanks, except those designed to need no maintenance within 10 years (see 9.6.2 b), are internally inspected, emptied and cleaned if necessary, examined for corrosion, repainted and/or their corrosion protection renewed | Clause 20.3.5.2, EN p.122 |
| 10 yearly | At intervals of not more than 10 years, all storage tanks are cleaned and internally inspected, and the structure is treated as required | Clause 20.3.6, EN p.122 |
Frequently Asked Questions
What are the water supply durations in EN 12845?
TS EN 12845+A2:2026 Clause 8.1.1 (EN p.42): LH 30 minutes, OH 60 minutes, HHP 90 minutes, HHS 90 minutes. The NOTE states that for town mains, inexhaustible sources and all pre-calculated systems the duration is implicit in the other requirements of the standard.
How is the tank volume determined for a fully calculated system?
Clause 9.3.2.3 (EN p.48): the minimum effective water volume is calculated by multiplying the maximum demand flow (Qmax) by the duration specified in Clause 8.1.1. For pre-calculated LH and OH systems Table 9 is used, and for pre-calculated HHP and HHS systems Table 10.
What is done if the tank is not protected against frost?
Clause 9.3.2.1 (EN p.47): where the tank is not frost resistant, the normal water level shall be raised by at least 1.0 m and ice venting shall be provided. The effective capacity of the tank is calculated as the difference between the normal water level and the lowest effective water level.
At what temperature are the supply pipe and control valve set kept?
Clause 8.1.3 (EN p.42): the supply pipe and the control valve set shall be maintained at a minimum temperature of 4 °C. Clause 9.5.2 (EN p.54) also requires at least 4 °C for the pressure tank and its housing. For the pump set compartment Clause 10.3.3 (EN p.58) requires 4 °C for electric and 10 °C for diesel.
What sprinkler count limits apply when antifreeze is used?
Clause 11.1.2.2 (EN p.66): the number of sprinklers in any section of pipe protected by antifreeze solution shall not exceed 20. Where one control valve set controls more than two antifreeze sections, the total number of sprinklers in the antifreeze sections shall not exceed 100. The freezing point of the solution shall be below the expected minimum temperature of the location, the specific gravity of the prepared solution shall be checked with a suitable hydrometer, and backflow prevention devices shall be fitted to prevent contamination of the water.
How quickly must the tank be refilled?
Clause 9.3.3 (EN p.48): for full capacity tanks the water supply shall be capable of refilling the tank in not more than 36 hours. The outlet of the supply pipe shall be at least 2.0 m horizontally from the inlet of the suction pipe.
References
- TS EN 12845+A2:2026 Clause 8.1.1 Duration (EN p.42 / TSE p.45)
- TS EN 12845+A2:2026 Clause 8.1.2 Continuity (EN p.42 / TSE p.45)
- TS EN 12845+A2:2026 Clause 8.1.3 Frost protection (EN p.42 / TSE p.45)
- TS EN 12845+A2:2026 Clause 8.4 Housing of water supply equipment (EN p.44 / TSE p.47)
- TS EN 12845+A2:2026 Clause 7.3.2.1, Table 7 (EN p.40 / TSE p.43)
- TS EN 12845+A2:2026 Clause 9.3.2.1 General - effective capacity and ice venting (EN p.47 / TSE p.50)
- TS EN 12845+A2:2026 Clause 9.3.2.2, Table 9 and Table 10 (EN p.47-48 / TSE p.50-51)
- TS EN 12845+A2:2026 Clause 9.3.2.3 Calculated systems (EN p.48 / TSE p.51)
- TS EN 12845+A2:2026 Clause 9.3.3 Infill rate for full capacity tanks (EN p.48 / TSE p.51)
- TS EN 12845+A2:2026 Clause 9.3.4, Table 11 Reduced capacity tanks (EN p.48-49 / TSE p.51-52)
- TS EN 12845+A2:2026 Clause 9.5.2 Housing of the pressure tank (EN p.54 / TSE p.57)
- TS EN 12845+A2:2026 Clause 9.7 Isolation of the water supply (EN p.57 / TSE p.60)
- TS EN 12845+A2:2026 Clause 10.3.3 Pump compartment temperature (EN p.58 / TSE p.61)
- TS EN 12845+A2:2026 Clauses 11.1.1, 11.1.2.1, 11.1.2.2, 11.1.2.3 (EN p.66-67 / TSE p.69-70)
- TS EN 12845+A2:2026 Clause 11.2.1 Dry pipe installations (EN p.67 / TSE p.70)
- TS EN 12845+A2:2026 Clauses 11.5.1, 11.5.2 Subsidiary dry pipe or alternate extension (EN p.69 / TSE p.72)
- TS EN 12845+A2:2026 Clauses 20.2.2.2, 20.2.2.6, 20.3.4.4, 20.3.5.2, 20.3.6 (EN p.119-122 / TSE p.122-125)
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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.