Source: EN 12845-2:2024 Clause 4 (EN p. 6), Clause 5.1.1 (EN p. 7), Clause 6.5 (EN p. 35), Clauses 6.7.1 and 6.7.2 (EN p. 48, 55 to 56); TS EN 12845+A2:2026 Clause 11 (EN p. 66-69).
The answer to the question of ESFR in an unheated warehouse is a single sentence in the standard, and it is the opposite of what is usually assumed: there is no dry ESFR installation. This article sets out the unheated area provisions of the two standards as they stand.
Clause 4 and Clause 6.5: ESFR is wet only
- Clause 4 (EN p. 6): "ESFR sprinklers shall only be used in wet installations. CMSA sprinklers can be used in wet and dry installations."
- Clause 6.5 (EN p. 35): "There is no dry installation option for this ESFR concept. Where dry pendent ESFR sprinklers are used the installation is considered a wet installation."
In other words, ESFR protection in an unheated space is achieved not by installing a dry pipe installation but by solving the unheated part of the wet installation. The solution the standard offers is dry pendent sprinklers and propylene glycol.
Antifreeze protection with propylene glycol (Clause 6.5)
| Requirement | Value |
|---|---|
| Minimum k-factor | 320 |
| Premixed antifreeze solution | At most 30 % glycol by volume; manufactured specifically for sprinkler systems |
| Pipework arrangement | Tree type |
| Conditional upper limit | In the same K320 and larger systems, up to 40 % by volume if it is demonstrated that water reaches a sprinkler within 60 s |
| After 60 s | At most 5 % glycol by volume may be present |
| Hydraulic calculation | The demand is calculated on the basis of a wet installation |
On the EN 12845 side the general antifreeze provision is in Clause 11.1.2.2 (EN p. 66): the number of sprinklers in a pipe section shall not exceed 20, and where a single control valve set has more than two antifreeze sections the total number of sprinklers shall not exceed 100; the freezing point of the solution shall be below the expected minimum temperature of the area; the specific gravity is checked with a suitable hydrometer; and a backflow prevention device is fitted to prevent contamination of the water.
The CMSA side: a dry installation is possible
- Clause 5.1.1 (EN p. 7): 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): CMSA sprinklers typically have a nominal operating temperature of 68 °C to 74 °C; in dry systems generally 141 °C.
- Clause 6.7.1 (EN p. 48): in a dry CMSA design the water delivery time is 40 s with 4 sprinklers operating, unless otherwise stated in the design table.
- Clause 6.7.2 (EN p. 55-56): upright, standard response ceiling level CMSA sprinklers with a nominal rating of 141 °C are used on a tree (end fed) dry pipe or similar system. Gridded or looped systems shall not be used. Where pre-action or interlocked systems are used, linear heat detection (LHD) is used as the heat detection to trigger the system; the line is run around the range pipes so as to obtain the same detection pattern as the sprinklers. In that arrangement the LHD may also be used to shut down the ventilation.
Table 21 (EN p. 55) gives the special dry pipe CMSA ceiling designs, and each row carries columns for the maximum water delivery time (20, 25, 30 or 60 s) and the system duration (90 or 120 min). Examples: HHS1, storage 10.7 m, ceiling 12.2 m, aisle 1.8 m, 12 sprinklers at 3.5 bar with K360 or K480, water delivery 20 s, duration 90 min; in the same row with an aisle of 1.2 m, 24 sprinklers at 1.0 bar with K360, water delivery 25 s, duration 120 min.
The EN 12845 side: installation types and freezing
Wet installations and frost protection
- Clause 11.1.1 (EN p. 66): wet pipe installations are installed only in areas where there is no possibility of freezing damage to the installation and where the ambient temperature will not exceed 95 °C.
- Clause 11.1.2.1: sections that may be exposed to freezing may be protected by antifreeze liquid, electrical trace heating, or a subsidiary dry pipe or alternate extension.
- Clause 11.1.2.3: trace heating requires duplicate elements, each able alone to maintain the pipe at not less than 4 °C, monitoring and switching by separate circuits, at least 25 mm of Euroclass A1 or A2 insulation with a waterproof covering, and a maximum rating of 10 W/m.
- Clause 8.1.3 (EN p. 42): the supply pipe and the control valve set are maintained at a minimum of 4 °C.
- Clause 10.3.3 (EN p. 58): the pump set room is kept at or above 4 °C for electrically driven sets and 10 °C for diesel driven sets.
- Clause 20.2.2.6 (EN p. 120): in the weekly routine the heating systems that prevent freezing are checked for correct function.
Dry pipe installations
Clause 11.2.1 (EN p. 67): dry pipe installations are normally charged with air or inert gas under pressure downstream of the dry alarm valve and with water under pressure upstream of it. A permanent air or inert gas supply is installed to maintain the pressure in the pipework, and the installation is pressurized to fall within the pressure range recommended by the alarm valve supplier. Dry pipe installations are used only where there is a possibility of freezing damage or where the temperature exceeds 70 °C (for example drying ovens).
The standard gives no numerical air pressure, water pressure or air to water ratio here; the criterion is the supplier's range.
Clause 11.2.2 (EN p. 67): the maximum time between a single sprinkler opening and water discharging shall not exceed the value in Table 18; the test is carried out with the remote test valve of Clause 15.5.2.
Table 18: maximum water delivery time, dry and alternate installations
| LH | OH and HH |
|---|---|
| 90 s | 60 s |
The same clause strongly recommends that dry and alternate installations should not be used for HHS applications, since the delay in water reaching the first operating sprinklers could seriously impair the effectiveness of the system. NOTE: experience showed that with an accelerator a volume of no more than 4 m³ for LH or OH and 3 m³ for HH occupancies is expected to fulfil the requirements of 11.2.2.
Alternate and pre-action installations
Clause 11.3.1 (EN p. 68): alternate installations incorporate either an alternate alarm valve or a composite set comprising a wet alarm valve and a dry alarm valve. During the winter months the pipework downstream of the alarm valve is charged with air or inert gas under pressure and the part upstream with water; at other times of the year the system operates as a wet pipe installation. The maximum water delivery time is again subject to Table 18.
Clause 11.4.1 (EN p. 68): pre-action installations are of two types.
- Type A: the control valve set is activated by an automatic fire detection system but not by the operation of the sprinklers. The air or inert gas pressure is monitored at all times; at least one quick opening manually operated valve is installed in an appropriate position so that the pre-action valve can be activated in an emergency. In the event of a fault in the detection system the installation operates as an ordinary dry pipe system. NOTE: Type A is only recommended in areas where considerable damage could occur if there was an accidental discharge of water.
- Type B: the control valve set is activated both by the automatic fire detection system and by the operation of the sprinklers. A pressure drop in the pipework opens the alarm valve independently of the response of the detectors.
The terminology of single interlock, double interlock or non-interlock does not appear in the text of the standard.
Clause 11.4.1.4 (EN p. 68-69): where a sprinkler system has more than one pre-action installation, a risk assessment is carried out to determine whether more than one of them could operate simultaneously. Where simultaneous filling is possible: the volume of the stored water supplies is increased by the total volume of the pre-action installations, and the time between the triggering of more than one pre-action installation and the discharge of water from any remote test valve on those installations shall not exceed 60 s.
Subsidiary dry pipe or alternate extensions
Clause 11.5 (EN p. 69): subsidiary extensions conform to 11.2 and 11.3 except that they are of limited extent and form extensions to normal wet installations. They are installed in only two cases: a dry or alternate extension to a wet pipe installation in small areas of an otherwise adequately heated building where there is a possibility of freezing damage; and a dry extension to a wet or alternate installation in cold stores and in high temperature ovens or furnaces. The number of sprinklers on an extension shall not exceed 100, and where a single control valve set controls more than two extensions the total shall not exceed 250.
Pipework details in dry systems
- Clause 12.1.3 (EN p. 70): except where dry pendent sprinklers are used, sprinklers in dry pipe, alternate and pre-action installations shall be upright; the yoke arms of an upright sprinkler are fitted parallel to the pipe.
- Clause 17.1.2 (EN p. 111): for dry, alternate or pre-action installations galvanized steel should be preferred.
- Clause 17.1.8 (EN p. 112): in dry, alternate and pre-action installations range pipes have a fall of at least 0.4 % towards the distribution pipe and distribution pipes a fall of at least 0.2 % towards the drain valve.
- Clause 19.1.1.1 (EN p. 117): dry pipework is tested pneumatically at not less than 2.5 bar for at least 24 hours; any pressure loss greater than 0.15 bar in 24 hours is corrected.
- Clause 20.2.2.2 a) (EN p. 119): in dry, alternate and pre-action installations the pressure in the pipework should not fall faster than 1.0 bar per week.
- Clause 20.3.3.2 (EN p. 121): the moving parts of dry alarm valves, accelerators and exhausters are operated every six months in accordance with the supplier's instructions. NOTE: alternate installations do not need to be tested in this way, since they are already operated as a result of the changeover from wet to dry and from dry to wet twice a year.
Frequently Asked Questions
Can ESFR be installed as a dry pipe installation?
No. EN 12845-2:2024 Clause 4 (EN p. 6) is clear: ESFR sprinklers are used only in wet installations. Clause 6.5 (EN p. 35) repeats this: there is no dry installation option for this ESFR concept, and where dry pendent ESFR sprinklers are used the installation is considered a wet installation. CMSA sprinklers may be used in wet and dry installations; in dry CMSA systems only dry pendent and upright sprinklers are used (Clause 5.1.1, EN p. 7).
Can antifreeze be used with ESFR?
Yes, within limits. Clause 6.5 (EN p. 35): designs with propylene glycol are permitted provided that the k-factor is not less than 320, that the premixed antifreeze solution does not exceed 30 % glycol by volume, that the solution is manufactured specifically for sprinkler systems and that tree type pipework is used. In the same K320 and larger systems the glycol concentration may be raised to 40 % by volume if it can be demonstrated that water reaches a sprinkler within 60 seconds; after 60 seconds no more than 5 % glycol by volume may be present. The hydraulic calculation of the demand is based on a wet installation.
What is the maximum water delivery time in dry and alternate installations?
TS EN 12845+A2:2026 Table 18 (EN p. 67): the maximum time between a single sprinkler opening and water discharging is 90 seconds for LH and 60 seconds for OH and HH. The test is carried out with the remote test valve specified in Clause 15.5.2. The same clause strongly recommends that dry and alternate installations should not be used for HHS applications. On the EN 12845-2 side, the water delivery time for dry CMSA is 40 seconds with 4 sprinklers operating in accordance with Clause 6.7.1, unless otherwise stated in the design table; values of 20, 25, 30 and 60 seconds appear in Table 21.
How does EN 12845 classify pre-action installations?
TS EN 12845+A2:2026 Clause 11.4.1 (EN p. 68) defines two types. Type A: the control valve set is activated by an automatic fire detection system but not by the operation of the sprinklers; the air or inert gas pressure is monitored at all times, at least one quick opening manually operated valve is provided to activate the pre-action valve in an emergency, and in the event of a fault in the detection system the installation operates as an ordinary dry pipe system. Type B: the control valve set is activated both by the automatic detection system and by the operation of the sprinklers; a pressure drop in the pipework opens the alarm valve independently of the response of the detectors. The terminology of single, double or non-interlock does not appear in the text of the standard.
In which cases is a dry pipe installation used?
TS EN 12845+A2:2026 Clause 11.2.1 (EN p. 67): dry pipe installations are used only where there is a possibility of freezing damage or where the temperature exceeds 70 °C (for example drying ovens). The installation is charged with air or inert gas under pressure downstream of the dry alarm valve and with water under pressure upstream of it; a permanent air or inert gas supply is installed to maintain the pressure and the installation is pressurized to fall within the pressure range recommended by the alarm valve supplier. The standard gives no numerical air or water pressure value and no air to water ratio.
At what temperature are the supply pipe and the valve room kept in an unheated area?
TS EN 12845+A2:2026 Clause 8.1.3 (EN p. 42): the supply pipe and the control valve set are maintained at a minimum temperature of 4 °C. Clause 10.3.3 (EN p. 58) requires a minimum temperature of 4 °C in the pump set room for electrically driven pump sets and 10 °C for diesel driven pump sets. Clause 20.2.2.6 (EN p. 120) requires the weekly routine to include a check that the heating systems that prevent freezing are working correctly.
References
- EN 12845-2:2024 Clause 4 (EN p. 6), Clause 5.1.1 (EN p. 7) and NOTE 2 (EN p. 8)
- EN 12845-2:2024 Clause 6.5 (EN p. 35)
- EN 12845-2:2024 Clause 6.7.1 (EN p. 48)
- EN 12845-2:2024 Table 21, Clause 6.7.2 (EN p. 55-56)
- TS EN 12845+A2:2026 Clause 8.1.3 (EN p. 42), Clause 10.3.3 (EN p. 58)
- TS EN 12845+A2:2026 Clause 11.1.1, 11.1.2.1, 11.1.2.2, 11.1.2.3 (EN p. 66)
- TS EN 12845+A2:2026 Clause 11.2.1, 11.2.2, Table 18 (EN p. 67)
- TS EN 12845+A2:2026 Clause 11.3.1, 11.4.1.2, 11.4.1.3 (EN p. 68)
- TS EN 12845+A2:2026 Clause 11.4.1.4, 11.5 (EN p. 68-69)
- TS EN 12845+A2:2026 Clause 12.1.3 (EN p. 70)
- TS EN 12845+A2:2026 Clause 17.1.2 (EN p. 111), Clause 17.1.8 (EN p. 112)
- TS EN 12845+A2:2026 Clause 19.1.1.1 (EN p. 117)
- TS EN 12845+A2:2026 Clause 20.2.2.2, 20.2.2.6 (EN p. 119-120), Clause 20.3.3.2 (EN p. 121)
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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.