The first step in sprinkler design is to determine the hazard class; Clause 6.1 of TS EN 12845+A2:2026 (EN 12845:2015+A2:2026) (EN p.30) says so explicitly: the hazard class for which the sprinkler system is to be designed shall be determined before the design work is started. Annex A (normative, EN p.124-126) gives the occupancy lists to be used in making that determination. All the lists and figures below are taken from the text of the standard.
1. The status of Annex A
The opening sentence of Annex A (EN p.124) says three things:
- Tables A.1, A.2 and A.3 contain lists of minimum hazard classification.
- They shall also be used as a guide for occupancies not specifically mentioned.
- They shall be read together with Clause 6.2.
In other words, Annex A is normative, the value it gives is a minimum, and an occupancy falling outside the table is derived from its closest equivalent.
2. Definitions of the classes (Clause 6.2, EN p.31-32)
- LH (Light Hazard): occupancies with low fire load and low combustibility, with no single compartment greater than 126 m² and with a fire resistance of at least 30 min.
- OH (Ordinary Hazard): occupancies where combustible materials with a medium fire load and medium combustibility are processed or manufactured; divided into four groups, OH1, OH2, OH3 and OH4.
- HHP (High Hazard, Process): occupancies where the materials involved have a high fire load and high combustibility and can develop a rapidly spreading or intense fire; divided into four groups, HHP1 to HHP4. NOTE: HHP4 hazards are generally protected by deluge systems, which are not within the scope of this standard.
- HHS (High Hazard, Storage): storage of goods at heights exceeding the limits given in 6.2.3; divided into four categories, HHS1 to HHS4. Examples are in Annex B and Annex C.
Storage in OH areas (Clause 6.2.3, EN p.31): materials may be stored in occupancies classified as OH, but under the following conditions: (a) the protection shall be designed to at least OH3 throughout the room; (b) the maximum storage heights shown in Table 1 shall not be exceeded; (c) the maximum storage area of a single block shall not exceed 50 m² and there shall be a clearance of at least 2.4 m around the block. Where the area is classified as OH4, or where (b) or (c) cannot be met, the storage in the area shall be treated as HHS (6.2.4.2).
Table 1 (EN p.32) - Maximum storage heights for OH3 protection (m):
| Storage category | Free standing or block stacking (ST1) | Other configurations (ST2 - ST6) |
|---|---|---|
| Category I | 4.0 | 3.5 |
| Category II | 3.0 | 2.6 |
| Category III | 2.1 | 1.7 |
| Category IV | 1.2 | 1.2 |
Footnote a: for storage heights exceeding the values in the table, HHS protection is used (6.2.4.2 and 7.2). Footnote b: ST6 storage is limited to gondola shelving of 1.2 m overall width with a solid central barrier extending from base to top; all other ST6 storage is protected in accordance with HHS protection (7.2).
3. Table A.1: Light Hazard occupancies (EN p.124)
- Schools and other educational establishments (certain areas, see 6.2.2)
- Offices (certain areas, see 6.2.2)
- Prisons
4. Table A.2: Ordinary Hazard occupancies (EN p.124-125)
| Group | OH1 | OH2 | OH3 | OH4 |
|---|---|---|---|---|
| Glass and ceramics | - | - | Glass works | - |
| Chemicals | Cement works | Photographic film factories | Dye works, soap factories, photographic laboratories, paint spraying shops using water based paints | - |
| Engineering | Sheet metal product works | Metal working | Electronics factories, radio equipment factories, washing machine factories, car service stations | - |
| Food and drink | - | Abattoirs and meat factories, bakeries, biscuit factories, breweries, chocolate factories, confectioneries, dairies | Animal feed factories, corn mills, dried vegetable and soup factories, sugar factories | Distilleries |
| Miscellaneous | Hospitals, hotels, libraries (excluding book storage), restaurants, schools (see 6.2.2), offices (see 6.2.2) | Laboratories (physical), laundries, car parks, museums | Broadcasting studios (small), railway stations, plant rooms, farm buildings | Cinemas and theatres, concert halls, tobacco factories, film and TV production studio |
| Paper | - | - | Bookbinders, cardboard factories, paper mills | Waste paper processing |
| Shops and offices | Data processing (computer room, excluding tape storage), offices (see 6.2.2) | - | Shops, shopping centres | Exhibition halls ᵃ |
| Textile and clothing | - | Leather goods factories | Carpet factories (excluding rubber and foamed plastics), cloth and clothing factories, fibreboard factories, shoe factories (excluding plastics and rubber), knitwear factories, linen factories, mattress factories (excluding foamed plastics), making-up factories, weaving mills, woollen and worsted mills | Cotton mills, flax preparation plants, hemp preparation plants |
| Timber and wood | - | - | Woodworking factories, furniture factories (without foamed plastics), furniture showrooms, upholstery (without foamed plastics) factories | Sawmills, plywood factories |
NOTE (below Table A.2, EN p.125): where there are paint spraying or similar high fire load areas within an OH1 or OH2 occupancy, these should be treated as OH3.
Footnote a: excessive clearance shall be taken into account.
5. Table A.3: High Hazard Process occupancies (EN p.126)
| HHP1 | HHP2 | HHP3 | HHP4 |
|---|---|---|---|
| Oilcloth and linoleum manufacture | Fire lighter manufacture | Cellulose nitrate manufacture | Firework manufacture |
| Resin, lamp black and turpentine manufacture | Tar distillation | Car and lorry tyres | - |
| Rubber substitute manufacture | Bus, empty lorry and wagon depots | Manufacture of foamed plastics with material factor m3 (see Table B.1), sponge rubber and sponge rubber goods (excluding m4, see Table B.1) | - |
| Wood wool manufacture | Candle and paraffin manufacturers | - | - |
| Match manufacturers | Paper machine rooms | - | - |
| Paint spraying shops using solvents | Carpet factories containing rubber and foamed plastics | - | - |
| Refrigerator factories | Sawmill | - | - |
| Printing works | Chipboard manufacture (see NOTE) | - | - |
| Cable factories of PP/PE/PS or similar burning characteristics (other than OH3) | - | - | - |
| Paint, colour and varnish manufacture | - | - | - |
| Injection moulding (plastics) of PP/PE/PS or similar burning characteristics (other than OH3) | - | - | - |
| Plastics factories and plastic products (excluding foamed plastics) of PP/PE/PS or similar burning characteristics (other than OH3) | - | - | - |
| Rubber goods factories, synthetic fibre factories (excluding acrylics) | - | - | - |
| Rope factories | - | - | - |
| Carpet factories containing non-expanded plastics | - | - | - |
| Shoe factories containing plastics and rubber | - | - | - |
NOTE: additional object protection may be required.
6. From the class to the design criteria
Table 3 (Clause 7.1, EN p.36) converts the class directly into a design density and an area of operation:
| Hazard class | Design density (mm/min) | Area of operation, wet or pre-action (m²) | Area of operation, dry or alternate (m²) |
|---|---|---|---|
| LH | 2.25 | 84 | Not permitted, OH1 is used |
| OH1 | 5.0 | 72 | 90 |
| OH2 | 5.0 | 144 | 180 |
| OH3 | 5.0 | 216 | 270 |
| OH4 | 5.0 | 360 | Not permitted, HHP1 is used |
| HHP1 | 7.5 | 260 | 325 |
| HHP2 | 10.0 | 260 | 325 |
| HHP3 | 12.5 | 260 | 325 |
| HHP4 | deluge (see NOTE) | - | - |
For HHS the design criteria come by a different route: Table 4 (roof or ceiling protection only, Clause 7.2.2, EN p.38) and Table 5 (roof or ceiling sprinklers with in-rack sprinklers, Clause 7.2.3, EN p.39). In these two tables the input variables are the storage configuration (ST1-ST6), the commodity category (I-IV) and the maximum storage height; the outputs are the density (from 7.5 mm/min to 30.0 mm/min) and the area of operation (260 m² or 300 m²).
Clause 7.2.3.2 (EN p.37): where intermediate level in-rack sprinklers are present, the design density for the roof or ceiling sprinklers shall be at least 7.5 mm/min over an area of operation of 260 m²; where goods are stored above the highest intermediate protection level, the design criteria are taken from Table 5.
7. When two classes occur together
The last sentence 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.
A similar rule applies to the categorisation of stored goods. Clause B.3.1 (EN p.129): once the material factor has been determined, the storage configuration in column 1 of Table B.1 is used to identify the most appropriate category; where Table C.1 also gives an appropriate category, the higher of the two shall be used.
8. Other clauses that affect the classification
- Clause 5.4 (EN p.30): protection in concealed spaces shall be to LH where the main hazard class is LH, and to OH1 in all other cases.
- Clause 14.2.2 (EN p.104): ceiling, flush, recessed and concealed type sprinklers shall not be installed in OH4, HHP or HHS areas.
- Clause 14.2.3 (EN p.104): sidewall sprinklers shall not be installed in HH installations (other than for the protection of corridors, cable ducts and columns) nor in OH storage areas.
- Table 19 (Clause 12.2, EN p.70): the maximum area per sprinkler is 21.0 m² in LH, 12.0 m² in OH and 9.0 m² in HHP and HHS; the maximum spacing is 4.6 m, 4.0 m and 3.7 m respectively.
- Clause 12.1.2 (EN p.70): the clear distance to be maintained below the deflector of roof and ceiling sprinklers is 0.3 m for flat spray sprinklers in LH and OH and 0.5 m in all other cases; 1.0 m for HHP and HHS.
- Clause 13.4.4 (EN p.102): the minimum sprinkler discharge pressure is 0.70 bar in LH, 0.35 bar in OH and 0.50 bar in HHP and HHS (excluding in-rack).
- Table 37a (Clause 14.2.1, EN p.104): the k-factor is 57 in LH, 80 or 115 in OH, and for HHP and HHS ceiling sprinklers 80, 115 or 160 where the density is ≤10 mm/min and 115 or 160 where it is >10 mm/min.
- Clause 8.1.1 (EN p.42): the water supply duration is LH 30 min, OH 60 min, HHP 90 min, HHS 90 min.
Frequently Asked Questions
Is Annex A binding, or is it only a list of examples?
The opening of Annex A (normative) of TS EN 12845+A2:2026, EN p.124: Tables A.1, A.2 and A.3 contain lists of minimum hazard classification. They shall also be used as a guide for occupancies not specifically mentioned. They shall be read together with Clause 6.2. In other words, Annex A is normative and the value it gives is a minimum.
What is the numerical criterion for the LH class?
Clause 6.2.2, EN p.31: LH covers occupancies with low fire load and low combustibility, with no single compartment greater than 126 m² and with a fire resistance of at least 30 min. Table A.1 (EN p.124) lists the LH occupancies: schools and other educational establishments (certain areas), offices (certain areas) and prisons.
Which hazard class do museums fall into?
Table A.2, EN p.125: Museums are listed in the OH2 column, in the same column as Laboratories (physical), Laundries and Car parks.
Which class covers cinemas, theatres and concert halls?
Table A.2, EN p.125: Cinemas and theatres, Concert halls, Tobacco factories and Film and TV Production Studio are in the OH4 column.
What design density and area correspond to each hazard class?
Table 3, Clause 7.1, EN p.36: LH 2.25 mm/min and 84 m²; OH1 5.0 mm/min and 72 m²; OH2 5.0 mm/min and 144 m²; OH3 5.0 mm/min and 216 m²; OH4 5.0 mm/min and 360 m²; HHP1 7.5 mm/min, HHP2 10.0 mm/min, HHP3 12.5 mm/min, all three over 260 m². These areas are for wet or pre-action systems.
Which class applies where two different classes exist in the same building?
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. For stored goods, Clause B.3.1 (EN p.129): where Table B.1 and Table C.1 give different categories, the higher of the two shall be used.
References
- TS EN 12845+A2:2026 (EN 12845:2015+A2:2026), Clause 5.4 (EN p.30)
- TS EN 12845+A2:2026, Clauses 6.1 and 6.2.1-6.2.4 (EN p.30-32)
- TS EN 12845+A2:2026, Table 1 and its footnotes (EN p.32)
- TS EN 12845+A2:2026, Clause 7.1 and Table 3 (EN p.35-36)
- TS EN 12845+A2:2026, Clause 7.2.2 and Table 4 (EN p.36-38)
- TS EN 12845+A2:2026, Clause 7.2.3.2 and Table 5 (EN p.37-39)
- TS EN 12845+A2:2026, Clause 8.1.1 (EN p.42)
- TS EN 12845+A2:2026, Clause 12.1.2 and Table 19 (EN p.70)
- TS EN 12845+A2:2026, Clause 13.4.4 (EN p.102)
- TS EN 12845+A2:2026, Table 37a, Clauses 14.2.2 and 14.2.3 (EN p.104)
- TS EN 12845+A2:2026, opening of Annex A and Table A.1, Table A.2 (EN p.124-125)
- TS EN 12845+A2:2026, Table A.3 (EN p.126)
- TS EN 12845+A2:2026, Clause B.3.1 and Table B.1 (EN p.129)
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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.