Every number in sprinkler design, the density, the area of operation, the water volume, the duration, the pipe diameter, the K factor, the area per sprinkler, derives from the hazard class. TS EN 12845+A2:2026 sets out the classification in Clause 6 and leaves the examples of occupancies to the normative Annex A. Source: TS EN 12845+A2:2026, Clause 6, EN p.30-34 (TSE p.33-37) and Annex A, EN p.124-126 (TSE p.127-129).
1. General (Clause 6.1)
Clause 6.1 (EN p.30):
The hazard class for which the sprinkler system is to be designed shall be determined before the design work is started. Buildings and areas to be protected by an automatic sprinkler system shall be classified as Light Hazard, Ordinary Hazard or High Hazard. This classification depends on the occupancy and the fire load. Examples of occupancies are given in Annex A.
The last sentence of the clause (EN p.31) is the rule for adjoining areas:
Where there are areas of different hazard classification in open communication, the higher design criteria shall be extended into the area of lower classification by at least two rows of sprinklers.
2. LH, Light Hazard (Clause 6.2.2)
LH covers occupancies with low fire loads and low combustibility, with no single compartment greater than 126 m² and having a fire resistance of at least 30 minutes. See Annex A for examples. Clause 6.2.2, EN p.31
Table A.1 (EN p.124) lists three items as Light Hazard occupancies: schools and other educational institutions (certain areas, see 6.2.2), offices (certain areas, see 6.2.2) and prisons.
The hydraulic counterpart of LH: a density of 2.25 mm/min, an area of operation of 84 m², and dry and alternate systems not permitted (Table 3, EN p.36). The counterpart on the sprinkler side: a nominal K factor of 57 and the conventional, spray, ceiling, flush, flat spray, recessed, concealed and sidewall types (Table 37a, EN p.104). The maximum area per sprinkler is 21.0 m² (Table 19, EN p.70).
3. OH, Ordinary Hazard (Clause 6.2.3)
OH covers occupancies where combustible materials with a medium fire load and medium combustibility are processed or manufactured. Clause 6.2.3, EN p.31
OH is divided into four groups: OH1, OH2, OH3 and OH4.
Storage within an OH area
Clause 6.2.3 states that materials may be stored in occupancies classified as OH provided three conditions are met:
- a) the protection throughout the room shall be designed to at least OH3;
- 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, with a clearance of not less than 2.4 m around the block.
Where the area is classified as OH4, or where conditions b) or c) cannot be met, the storage within the area is treated as HHS (see Clause 6.2.4.2).
Table 1: Maximum storage heights for OH3 protection
| Storage category | Free standing or block stacking (ST1) | Storage configurations (ST2 - ST6) |
|---|---|---|
| Category I | 4.0 m | 3.5 m |
| Category II | 3.0 m | 2.6 m |
| Category III | 2.1 m | 1.7 m |
| Category IV | 1.2 m | 1.2 m |
Source: Table 1, Clause 6.2.3, EN p.32 (TSE p.35).
The two footnotes to the table: (a) where the storage heights exceed the values in the table, HHS protection is used, see 6.2.4.2 and 7.2. (b) ST6 storage is limited to gondola shelving with a solid central barrier extending from the floor to the top of the gondola shelving, with a total width of 1.2 m. All other ST6 storage requires protection to HHS, see 7.2.
4. HH, High Hazard (Clause 6.2.4)
HHP, High Hazard Process (Clause 6.2.4.1, EN p.32): covers occupancies where the materials involved have a high fire load and high combustibility and can develop a rapidly spreading or intense fire. It is divided into four groups: HHP1, HHP2, HHP3 and HHP4. NOTE: HHP4 hazards are usually protected by deluge systems, which are outside the scope of this standard.
HHS, High Hazard Storage (Clause 6.2.4.2, EN p.32): covers the storage of goods whose heights exceed the limits given in Clause 6.2.3. It is divided into four categories: HHS1 (Category I), HHS2 (Category II), HHS3 (Category III) and HHS4 (Category IV). NOTE: examples are given in Annex B and Annex C.
5. Storage: material factor and configuration (Clause 6.3)
Clause 6.3.1 (EN p.33): the overall fire hazard of stored goods is a function of the combustibility of the stored materials, including their packaging, and of the storage configuration. Where stored goods are concerned, the procedure in Figure 2 is followed to determine the required design criteria.
Clause 6.3.2 (EN p.33) defines six storage configurations:
| Code | Configuration |
|---|---|
| ST1 | Free standing or block stacking |
| ST2 | Post pallets in single rows, aisles not narrower than 2.4 m |
| ST3 | Post pallets in multiple rows (including double) |
| ST4 | Palletized racking (beam pallet racking) |
| ST5 | Solid or slatted shelves, width 1 m or less |
| ST6 | Solid or slatted shelves, width more than 1 m and not more than 6 m |
Clause 6.3.2 also states that, for the sprinkler protection to be effective, the limitation and protection requirements of Table 2 have to be met. Table 2 (EN p.34) gives, for each configuration, the maximum storage block area, the width of the aisles separating the storage rows and the minimum separating clearance around the storage block area; for ST1, for example, the maximum block area is 50 m² with a clearance of 2.4 m for OH, and 150 m² with 2.4 m for HH.
Determining the material category is the subject of the normative Annex B. Clause B.2.1 (EN p.127) states that four material factors are to be used in determining the category, that goods are to be assessed including their packaging and pallet material, and that for the purpose of this assessment rubber is treated in the same way as plastics. Under Clause B.2.2, Material Factor 1 covers non-combustible products in combustible packaging and products of low or medium combustibility in combustible or non-combustible packaging: less than 5 % unexpanded plastics content by mass and less than 5 % expanded plastics content by volume, including the pallet.
6. Annex A: the lists of occupancies
Annex A is normative and its introduction (EN p.124) states:
Tables A.1, A.2 and A.3 contain lists of minimum hazard classification. They shall also be used as guidance for occupancies not specifically mentioned. They shall be read in conjunction with 6.2.
The word "minimum" is critical: the list gives a lower bound, not a ceiling.
Selected rows from Table A.2 (EN p.124-125)
| Occupancy group | OH1 | OH2 | OH3 | OH4 |
|---|---|---|---|---|
| Glass and ceramics | - | - | Glass factories | - |
| Chemicals | Cement works | Photographic film factories | Dyers works; soap factories; photographic laboratories; paint application shops with water based paint | - |
| Engineering | Sheet metal product factories | Metal working | Electronics factories; radio equipment factories; washing machine factories; car workshops | - |
| Food and beverages | - | Abattoirs and meat factories; bakeries; biscuit factories; breweries; chocolate factories; confectionery; dairies; factories | Animal fodder factories; corn mills; dehydrated vegetable and soup factories; sugar factories | Alcohol distilleries |
| Miscellaneous | Hospitals; hotels; libraries (excluding book stores); restaurants; schools (see 6.2.2); offices (see 6.2.2) | Laboratories (physical); laundries; car parks; museums | Broadcasting studios (small); railway stations; plant (technical) room; farm building | Cinemas and theatres; concert halls; tobacco factories; film and TV production studio |
| Paper | - | - | Book binding factories; cardboard factories; paper factories | Waste paper processing |
| Shops and offices | Data processing (computer room, excluding tape storage); offices see 6.2.2 | - | Department stores; shopping centre | Exhibition halls (a) |
| Textiles and clothing | - | Leather goods factories | Carpet factories (excluding rubber and foam plastics); cloth and clothing factories; fibre board factories; footwear factories (excluding plastics and rubber); knitting factories; linen factories; mattress factories (excluding foam plastics); sewing factories; weaving mills; woollen and worsted mills | Cotton mills; flax preparation plants; hemp preparation plants |
| Timber and wood | - | - | Woodworking factories; furniture factories (without foam plastics); furniture showrooms; upholstery (without foam plastics) factories | Saw mills; plywood factories |
Source: Table A.2, Annex A, EN p.124-125 (TSE p.127-128). (a) Excessive clearance shall be taken into consideration.
The NOTE to Table A.2: "Where there is painting or other similar high fire load areas in an OH1 or OH2 occupancy, they should be treated as OH3."
Table A.3: High Hazard Process occupancies (EN p.126)
| Column | Occupancies |
|---|---|
| HHP1 | Floor cloth and linoleum manufacture; resin, lamp black and turpentine manufacture; rubber substitute manufacture; wood wool manufacture; match manufacturers; paint application shops with solvent; refrigerator factories; printing works; cable factories for PP/PE/PS or similar burning characteristics other than OH3; injection moulding (plastics) for PP/PE/PS or similar burning characteristics other than OH3; plastics factories and plastic goods (excluding foam plastics) for PP/PE/PS or similar burning characteristics other than OH3; rubber goods factories and synthetic fibre factories (excluding acrylic); rope factories; carpet factories including unexpanded plastics; footwear factories including plastics and rubber |
| HHP2 | Fire lighter manufacture; tar distilling; depots for buses, un-laden lorries and railway carriages; candle wax and paraffin manufacturers; paper machine halls; carpet factories including rubber and foam plastics; saw mill; chipboard manufacturing (see NOTE); paint, colour and varnish manufacture |
| HHP3 | Cellulose nitrate manufacture; rubber tyres for cars and lorries; manufacture of material factor m3 (see Table B.1): foam plastics, foam rubber and foam rubber goods manufacture (excluding m4, see Table B.1) |
| HHP4 | Firework manufacture |
Source: Table A.3, Annex A, EN p.126 (TSE p.129). NOTE: additional object protection might be necessary.
Several details of Table A.3 are frequently confused: match manufacturers are in HHP1 (not in Table A.2); saw mill appears both as OH4 in Table A.2 and in the HHP2 column of Table A.3; depots for buses and un-laden lorries are in HHP2; rubber tyres for cars and lorries are in HHP3; the manufacture of foam plastics and foam rubber (material factor m3) is in HHP3; plastics factories for PP/PE/PS (excluding foam plastics) are in HHP1.
7. From the class to the design values
| Class | Density (mm/min) | Area of operation, wet (m²) | Maximum area per sprinkler (m²) | Water duration (min) |
|---|---|---|---|---|
| LH | 2.25 | 84 | 21.0 | 30 |
| OH1 | 5.0 | 72 | 12.0 | 60 |
| OH2 | 5.0 | 144 | 12.0 | 60 |
| OH3 | 5.0 | 216 | 12.0 | 60 |
| OH4 | 5.0 | 360 | 12.0 | 60 |
| HHP1 | 7.5 | 260 | 9.0 | 90 |
| HHP2 | 10.0 | 260 | 9.0 | 90 |
| HHP3 | 12.5 | 260 | 9.0 | 90 |
| HHS | from Table 4/5 | from Table 4/5 | 9.0 | 90 |
Sources: Table 3 (Clause 7.1, EN p.36), Table 19 (Clause 12.2, EN p.70), Clause 8.1.1 (EN p.42), Table 4 and Table 5 (Clause 7.2, EN p.38-39).
The installation size also depends on the class (Table 17, Clause 11.1.3, EN p.67): LH 10 000 m², OH (including the LH sprinklers within it) 12 000 m² (except as permitted in Annexes D and F), HH (including the OH and LH sprinklers within it) 9 000 m².
Frequently Asked Questions
How is Light Hazard (LH) defined in EN 12845?
TS EN 12845+A2:2026 Clause 6.2.2 (EN p.31): LH covers occupancies with a low fire load and low combustibility, with no single compartment greater than 126 m² and having a fire resistance of at least 30 minutes. See Annex A for examples.
May goods be stored in areas classified as OH?
Clause 6.2.3 (EN p.31) permits it under three conditions: a) the protection throughout the room shall be designed to at least OH3; 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 a clearance of not less than 2.4 m shall be provided around the block. Where the area is classified as OH4, or where b) or c) cannot be met, the storage within the area is treated as HHS.
What are the maximum storage heights in Table 1?
Table 1 (Clause 6.2.3, EN p.32), for OH3 protection: free standing or block stacking (ST1) - Category I 4.0 m, Category II 3.0 m, Category III 2.1 m, Category IV 1.2 m. Storage configurations ST2 to ST6 - Category I 3.5 m, Category II 2.6 m, Category III 1.7 m, Category IV 1.2 m. Where the values in the table are exceeded, HHS protection is used.
What is the difference between HHP and HHS?
Clause 6.2.4.1 (EN p.32): HHP (High Hazard Process) covers occupancies where the materials involved have a high fire load and high combustibility and can develop a rapidly spreading or intense fire; it is divided into four, HHP1 to HHP4. Clause 6.2.4.2 (EN p.32): HHS (High Hazard Storage) covers the storage of goods whose heights exceed the limits given in 6.2.3 and is divided into four categories, HHS1 to HHS4.
Are the lists in Annex A binding?
Annex A is normative. Its introduction states: 'Tables A.1, A.2 and A.3 contain lists of minimum hazard classification. They shall also be used as guidance for occupancies not specifically mentioned. They shall be read in conjunction with 6.2.' (EN p.124). In other words the lists give the minimum class; where the actual fire load is higher, the class is raised.
What is done where two areas of different classes are in open connection?
At the end of Clause 6.1 (EN p.31): where there are areas of different hazard classification in open communication, the higher design criteria shall be extended into the area of lower classification by at least two rows of sprinklers.
References
- TS EN 12845+A2:2026 Clause 6.1 General and the two row rule (EN p.30-31 / TSE p.33-34)
- TS EN 12845+A2:2026 Clause 6.2.1 General (EN p.31 / TSE p.34)
- TS EN 12845+A2:2026 Clause 6.2.2 Light Hazard - LH (EN p.31 / TSE p.34)
- TS EN 12845+A2:2026 Clause 6.2.3, Table 1 Ordinary Hazard - OH (EN p.31-32 / TSE p.34-35)
- TS EN 12845+A2:2026 Clauses 6.2.4.1, 6.2.4.2 High Hazard (EN p.32 / TSE p.35)
- TS EN 12845+A2:2026 Clauses 6.3.1, 6.3.2, Table 2 Storage (EN p.33-34 / TSE p.36-37)
- TS EN 12845+A2:2026 Clause 7.1, Table 3 (EN p.35-36 / TSE p.38-39)
- TS EN 12845+A2:2026 Clause 7.2, Table 4 and Table 5 (EN p.38-39 / TSE p.41-42)
- TS EN 12845+A2:2026 Clause 8.1.1 Duration (EN p.42 / TSE p.45)
- TS EN 12845+A2:2026 Clause 11.1.3, Table 17 (EN p.67 / TSE p.70)
- TS EN 12845+A2:2026 Clause 12.2, Table 19 (EN p.70 / TSE p.73)
- TS EN 12845+A2:2026 Clause 14.2.1, Table 37a (EN p.104 / TSE p.107)
- TS EN 12845+A2:2026 Annex A introduction and Table A.1 (EN p.124 / TSE p.127)
- TS EN 12845+A2:2026 Annex A, Table A.2 (EN p.124-125 / TSE p.127-128)
- TS EN 12845+A2:2026 Annex A, Table A.3 (EN p.126 / TSE p.129)
- TS EN 12845+A2:2026 Annex B, Clauses B.2.1, B.2.2 (EN p.127 / TSE p.130)
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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.