A warehouse building is rarely only a warehouse: the dispatch hall, packing area, offices, plant rooms and maintenance workshop are usually under the same roof. TS EN 12845-2:2025 (EN 12845-2:2024) answers this situation with two clauses: Clause 6.2 determines where ESFR and CMSA may be used in non-storage occupancies, and Clause 6.3 determines how different protection concepts are separated. Every provision below is quoted from that standard or from TS EN 12845+A2:2026.
1. The critical limit: no ESFR or CMSA in FH3, FH4 and FH5
Clause 6.2 (EN p.33) is two sentences and defines the framework of the design on its own:
ESFR and CMSA protection shall not be applied to FH3 to FH5 occupancies. Where ESFR and CMSA sprinklers are used in FH1 and FH2 hazards, including the storage permitted for the relevant hazards in Table 2 of EN 12845:2015+A1:2019 (see Table A.1), they shall be designed as HHS1 to HHS3 in accordance with 6.6 or 6.7, irrespective of the storage category. All requirements relating to the installation of ESFR and CMSA shall apply.
The practical meaning of this provision emerges with Annex A Table A.1 (normative, EN p.59):
| EN 12845 class | EN 12845-2 class |
|---|---|
| LH | FH1 |
| OH1 | FH1 |
| OH2 | FH2 |
| OH3 | FH2 |
| OH4 | FH3 |
| HHP1 | FH4 |
| HHP2 | FH4 |
| HHP3 | FH5 |
Combining the two tables gives this result: ESFR and CMSA may be used in non-storage areas classified as LH, OH1, OH2 and OH3, but those areas are designed as HHS1-HHS3. ESFR and CMSA cannot be used in areas classified as OH4, HHP1, HHP2 and HHP3.
The determination of the hazard class itself is based on Annex A of EN 12845+A2 (EN p.124-126) and on Clause 6.2; EN 12845-2 Clause 4 (EN p.6) states that "Annex A shall be applied for the determination of FH and HHS".
A second piece of scope information is in the introductory text of Table 11 (EN p.41): all the designs in that table can protect HHS4 up to 20 m² with a storage height of up to 1.8 m or an FH (non-storage) risk excluding ignitable liquids.
2. How the hazard class is determined in a non-storage area
The classification comes from Clause 6 of EN 12845+A2:
- LH (Clause 6.2.2, EN p.31): occupancies with low fire load and low combustibility, with no single compartment exceeding 126 m² and with a fire resistance of at least 30 min. Examples are in Annex A.
- OH (Clause 6.2.3, EN p.31): occupancies where combustible materials with a medium fire load and medium combustibility are processed or manufactured; it is divided into four groups, OH1 to OH4. Storage is permitted in occupancies classified as OH only under the following conditions: (a) the protection is designed to at least OH3 throughout the room; (b) the maximum storage heights in Table 1 are not exceeded; (c) the maximum storage area of a single block does not exceed 50 m² and there is a clearance of at least 2.4 m around the block. If the area is classified as OH4, or if (b) or (c) cannot be met, the storage in the area is treated as HHS.
- Table 1 (EN p.32) gives the maximum storage heights for OH3 protection: in free standing/block stacking (ST1), Category I 4.0 m, Category II 3.0 m, Category III 2.1 m, Category IV 1.2 m; in the other configurations (ST2-ST6), 3.5 m, 2.6 m, 1.7 m and 1.2 m respectively.
3. Different hazard classes in open communication
End of Clause 6.1 of TS EN 12845+A2 (EN p.31): where there are areas in open communication with different hazard classifications, the higher design criteria shall be extended into the area of lower classification by at least two rows of sprinklers.
This rule determines how the transition between an ESFR/CMSA protected warehouse and a CMDA protected packing area opening off it is handled in a mixed building.
4. Separating different protection concepts (Clause 6.3, EN p.34)
EN 12845-2 Clause 6.3 requires a draft curtain at the ceiling in exactly these two situations:
- where the adjacent areas have the same ceiling height and different RTIs;
- where ESFR is installed at a higher ceiling height than the adjacent CMSA or standard sprinklers.
Properties of the curtain and the separation:
| Requirement | Value |
|---|---|
| Curtain depth | At least 600 mm |
| Curtain material | Non-combustible |
| Curtain position | Between the different sprinkler types; positioning in accordance with 5.1.3.8 |
| Width of the separating aisle | At least 1.2 m, clear of all stored goods |
| Centre of the aisle | Coincides with the mid-point between the different sprinkler types |
Clause 5.1.3.8 (EN p.12), referenced for the positioning of the curtain, carries two warnings: draft curtains should preferably not be installed within sprinkler arrays; where they are necessary, the sprinklers on either side of the curtain should be generally equidistant from it and the obstruction criteria shall be met. NOTE 2: draft curtains have been shown to have an adverse effect on sprinkler effectiveness; where they are necessary, special consideration is required to minimise the adverse effect.
5. Fire compartments and unprotected areas
TS EN 12845+A2 Clause 5.3 (EN p.30): the separation between a sprinkler protected area and an unprotected area shall have a fire resistance determined by the authority, but in no case less than 60 min. Doors shall be self-closing or shall close automatically in the event of fire. There should be no unprotected building or part of a building vertically below a sprinklered building or part (other than as stated in 5.1.2 and 5.1.3).
Clause 5.4 (EN p.30): where the height of a concealed space in the roof or floor exceeds 0.8 m, those spaces shall be protected by sprinklers. Where it does not exceed 0.8 m, they are protected only if they contain combustible material or are constructed of combustible material. The protection in the concealed space shall be to LH where the main hazard class is LH, and to OH1 in all other cases.
6. Installation size and mezzanines
The limit that governs the division of installations in a mixed building is Table 17 (Clause 11.1.3, EN p.67): the maximum protected area controlled by a single wet alarm valve is 10 000 m² in LH, 12 000 m² in OH (including LH sprinklers within it, other than those permitted in Annexes D and F), and 9 000 m² in HH (including OH and LH sprinklers within it).
Mezzanines are dealt with in EN 12845-2 Clause 5.2.7 (EN p.20-21): quick response or ESFR sprinklers shall be installed beneath solid mezzanines which have combustible construction and/or a combustible occupancy below them. Exception: standard response sprinklers may be installed where a row of sprinklers is not more than 0.6 m from the edge of the mezzanine and all the storage or combustible goods beneath the mezzanine lie within the boundary formed by these perimeter sprinklers, or where a draft curtain is provided around the mezzanine. The design of the sprinkler protection at mezzanine level is based on the height of the mezzanine and the occupancy beneath it; for the use of CMDA sprinklers, see EN 12845.
7. Pressure limit
Even though different zones in a mixed building operate at different pressures, there is a single upper limit: TS EN 12845+A2 Clause 8.2.1 (EN p.42): other than during testing, the water pressure at the equipment connections or locations defined in 8.2.1.1 and 8.2.1.2 shall not exceed 12 bar. The list in 8.2.1.1 covers, for all sprinkler systems, the sprinklers, multiple jet controls, water flow detectors, dry pipe and pre-action alarm valves, accelerators and exhausters, water motor alarms and zone control valves.
Field note: In a mixed building the real risk is that the ESFR or CMSA solution chosen for the warehouse does not match the occupancy class of the adjacent area. Classification comes first and the protection concept is chosen afterwards; in projects that proceed in the reverse order, Clause 6.2 sends the design back.
Frequently Asked Questions
Can ESFR and CMSA be used in non-storage areas?
TS EN 12845-2:2025 Clause 6.2, EN p.33: ESFR and CMSA protection shall not be applied to FH3 to FH5 occupancies. Where ESFR and CMSA sprinklers are used in FH1 and FH2 hazards, including the storage permitted for the relevant hazards in Table 2 of EN 12845:2015+A1:2019, they shall be designed as HHS1 to HHS3 in accordance with 6.6 or 6.7, irrespective of the storage category. All the requirements relating to the installation of ESFR and CMSA apply.
How are the FH classes converted to the EN 12845 hazard classes?
EN 12845-2:2024 Annex A Table A.1, EN p.59: LH → FH1, OH1 → FH1, OH2 → FH2, OH3 → FH2, OH4 → FH3, HHP1 → FH4, HHP2 → FH4, HHP3 → FH5. Read together with Clause 6.2, ESFR and CMSA cannot be used in areas of OH4 and above.
How are adjacent areas with different protection concepts separated?
Clause 6.3, EN p.34: a draft curtain shall be installed at the ceiling where adjacent areas have the same ceiling height and different RTIs, or where ESFR is installed at a higher ceiling than adjacent CMSA or standard sprinklers. The curtain shall be at least 600 mm deep, of non-combustible material, and positioned between the different sprinkler types. Between two areas with different protection concepts, an aisle at least 1.2 m wide and clear of all stored goods shall be maintained; the centre of the aisle shall coincide with the mid-point between the different sprinkler types.
How many minutes of fire resistance are required between sprinkler protected and unprotected areas?
TS EN 12845+A2:2026 Clause 5.3, EN p.30: the separation between a sprinkler protected area and an unprotected area shall have a fire resistance determined by the authority, but in no case less than 60 min. Doors shall be self-closing or shall close automatically in the event of fire.
What is done where different hazard classes are in open communication in the same building?
TS EN 12845+A2:2026, end of Clause 6.1, EN p.31: where there are areas in open communication with different hazard classifications, the higher design criteria shall be extended into the area of lower classification by at least two rows of sprinklers.
References
- TS EN 12845-2:2025 (EN 12845-2:2024), Clause 4 General (EN p.6)
- TS EN 12845-2:2025, Clause 5.1.3.8 Positioning relative to draft curtains (EN p.12)
- TS EN 12845-2:2025, Clause 5.2.7 Solid mezzanines (EN p.20-21)
- TS EN 12845-2:2025, Clause 6.2 Protection of non-storage occupancies with ESFR and CMSA (EN p.33)
- TS EN 12845-2:2025, Clause 6.3 Adjacent areas using a different protection concept (EN p.34)
- TS EN 12845-2:2025, introductory text of Table 11 (EN p.41)
- TS EN 12845-2:2025, Annex A Table A.1 (EN p.59)
- TS EN 12845+A2:2026, Clause 5.3 Fire resisting separation, Clause 5.4 Concealed spaces (EN p.30)
- TS EN 12845+A2:2026, end of Clause 6.1 - areas in open communication (EN p.31)
- TS EN 12845+A2:2026, Clauses 6.2.2 and 6.2.3 (EN p.31), Table 1 (EN p.32)
- TS EN 12845+A2:2026, Clause 8.2.1 (EN p.42)
- TS EN 12845+A2:2026, Clause 11.1.3 and Table 17 (EN p.67)
- TS EN 12845+A2:2026, Annex A (EN p.124-126)
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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.