EN 12845 Annex A: Typical Occupancy Hazard Classification

Schools, hospitals, factories, warehouses — reading the occupancy classification tables from a site perspective, and defensibly classifying a facility that is not on the list.

A logistics centre's safety report stated "office block, LH"; the insurer wrote back saying "open plan, no compartmentation, cable trays — that's OH1", and the project stopped for two days. The classification annex was opened, the hazard classification clause read, and the difference understood. The annex is an interpretable list, not something to be recited. This article separates the LH, OH1–OH4 and HHP1–HHP4 tables from a site perspective, clarifies the difference from the commodity annex, and covers how we reach a defensible class when the facility is "not on the list".

Where the classification annex sits

EN 12845:2015+A1:2019 defines hazard classification in its main clause, while the normative annex "Classification of typical hazards" links typical facility types to those classes through three tables. The standard's own wording is clear: the tables are a "minimum hazard classification" list, and also serve as "guidance for occupancies not specifically mentioned". So the list is both binding as a minimum and open to interpretation; matching an unlisted facility to its nearest analogue and adjusting upward is in keeping with the annex's intent.

It must be read alongside the classification clause, which places schools and offices conditionally under both LH and OH1, leaving the decision to fire load and compartmentation. Obtaining the view of the authority and the insurer is recommended — and is the wording of the clause itself.

Light hazard

The LH list is short: schools and educational establishments (certain areas), offices (certain areas) and prisons. In practice their fire load should stay below 800 MJ/m², with limited compartment area and controlled combustible content. The design values are 2.25 mm/min over an 84 m² area of operation.

Facility	Class	Note
Prison (cells, administration)	LH	Directly listed
Primary school classroom block	LH	If the clause conditions are met
Small cellular office (enclosed)	LH	Per the clause; otherwise OH1
Library reading room	OH1	Excluding book stores
Hospital ward block	OH1	Hospitals are on the OH1 list
Museum exhibition hall	OH1	Miscellaneous group

Note that hospitals, hotels, libraries (excluding book stores), restaurants and museums appear in the OH1 column. So hotels and hospitals, popularly assumed to be light hazard, are OH1 under the annex. LH is reserved for schools, offices, prisons and their analogues.

Ordinary hazard — four columns

In site language: OH1 is low combustibility, OH2 moderate, OH3 high (though not a heavy process), and OH4 covers facilities with thick combustible fibres such as textiles and timber. All use 5.0 mm/min density; what changes is the area of operation — 72, 144, 216 and 360 m² for wet systems.

Class	Typical facilities	Wet area of operation
OH1	Cement works, sheet metal product factories, hospitals, hotels, libraries, restaurants, museums, small broadcast studios, railway stations, plant rooms, farm buildings, cinemas and theatres, concert halls, tobacco factories, film and TV studios, data processing (computer room, excluding tape storage), water-based paint booths, offices	72 m²
OH2	Photographic film factories, metalworking, abattoirs and meat factories, bakeries, biscuit factories, breweries, chocolate factories, confectionery, dairies, physics laboratories, laundries, car parks, leather goods factories	144 m²
OH3	Glassworks, dye works, soap factories, photographic laboratories, electronics factories, radio equipment factories, washing machine factories, vehicle servicing, animal feed, corn mills, dried vegetable and soup factories, sugar factories, binderies, carton and paper factories, shopping centres and shops, carpet factories (excluding rubber and foam plastic), cloth, clothing and fibreboard factories, footwear (excluding plastics and rubber), knitwear and linen factories, synthetic mattresses (excluding foam plastic), sewing and weaving, woollen and cambric works, timber processing, furniture (excluding foam plastic), furniture showrooms, upholstery (excluding foam plastic)	216 m²
OH4	Alcohol distilling, waste paper processing, exhibition halls, cotton, flax and hemp preparation, timber mills, plywood factories	360 m²

The note beneath the OH list carries practical weight: where there is painting or another similar high fire load area within an OH1 or OH2 occupancy, it should be treated as OH3. So the spray booth inside a facility designed as OH1 is protected as OH3 — the whole facility need not be upgraded, but that zone moves class. Where the areas are openly connected, the higher value governs.

High hazard process

HHP1–HHP4 covers processes whose fire load and heat release rate exceed ordinary hazard. Design densities are 7.5, 10.0 and 12.5 mm/min respectively, over a common 260 m² area. HHP4 is usually solved with deluge or foam-water systems.

Class	Typical facilities	Density
HHP1	Linoleum manufacture, resin, lamp black and turpentine manufacture, rubber substitute manufacture, wood wool manufacture, match factories, solvent paint booths, cold store manufacture, printing works, PP/PE/PS cable, injection moulding (PP/PE/PS), plastics factories (excluding foam plastic), rubber goods, synthetic fibres (excluding acrylic), rope works, carpets (including unexpanded plastic), footwear (including plastics and rubber)	7.5 mm/min
HHP2	Firelighter manufacture, tar distillation, bus and empty lorry or wagon depots, paraffin wax manufacture, paper machine halls, carpets (including rubber and foam plastic), timber mills, particle board manufacture, paint, colour and varnish manufacture	10.0 mm/min
HHP3	Cellulose nitrate manufacture, car and truck tyres, foam plastic and foam rubber manufacture	12.5 mm/min
HHP4	Fireworks manufacture	Project specific — deluge or foam

Why high-hazard storage is absent

The high hazard process table addresses process load only. For storage, EN 12845 builds a different route: the material factor annex (M1–M4) with storage configuration gives Category I–IV, and the commodity annex gives the same category directly from an alphabetical product list. The high-hazard storage tables then produce a density-area combination from that category and rack height. So a warehouse is not classified as a facility type in the classification annex; it goes through a separate procedure.

The practical rule: where a building has both process and storage, the process area is classified from the classification annex and the storage area from the material factor and commodity annexes. Where they share a compartment with an open connection, the higher value governs the whole area.

Classification annex versus commodity annex

Dimension	Classification annex	Commodity annex
What it classifies	Facility type (factory, office, hospital)	Commodity (alcohol, paper, tyres, furniture)
Output	LH / OH1–4 / HHP1–4	Category I–IV
Field of use	Process and general occupancy	Storage calculation
Design input	Density-area tables	High-hazard storage density-height tables
Status	Normative, minimum list	Normative, alphabetical list

Where they overlap — a furniture showroom is OH3 in the classification annex and Category II as a commodity — the rule is that the higher of the two values is used. If the showroom's rack height passes 2 m and the building takes on the character of a store, the commodity route applies. Otherwise the classification annex OH3 is sufficient.

What to do when the facility is not listed

The standard addresses this: the annex also serves as guidance for occupancies not specifically mentioned. Our site sequence:

1. The nearest analogue: "data centre white space" is not listed, but data processing (computer room, excluding tape storage) is listed as OH1. With hot and cold aisle containment, OH1 is a sensible starting point; the backup tape area goes to the commodity annex.
2. Fire load calculation: in MJ/m², moved up or down relative to a comparable facility. EN 12845 gives no limits, but below 800 MJ/m² for LH and 800–2400 MJ/m² for OH has become standard insurer practice.
3. A written opinion from the authority and insurer: the classification clause explicitly asks for it. The decision is recorded in a technical note kept in the project file, and it saves the acceptance test.
4. Round upward: where in doubt, take the higher class. Choosing OH3 over OH2 only enlarges the area of operation; K-factor and pump selection do not change, but the site risk is covered.

Common errors

• Treating hotels and hospitals as light hazard: they are on the OH1 list.
• Leaving a spray booth zone as OH1: the note requires it to be treated as OH3.
• Assuming "library equals LH": the reading room is OH1, but book stores are excluded and must be classified through the storage route.
• Confusing wet and dry areas of operation for OH4: a dry system enlarges the area — from 72 to 90 m² for OH1 and by 25 % for OH2–4. That comes from the design clauses, not the classification annex.
• Assuming the list never repeats a product under different headings: footwear factories appear both as OH3 (without plastics) and HHP1 (with plastics and rubber). Selecting without reading the qualifier produces an error.

Comparison with NFPA

NFPA 13 gives its occupancy list as explanatory material rather than a normative table. The equivalences: LH corresponds to NFPA light hazard; OH1–OH2 to ordinary hazard group 1; OH3–OH4 to ordinary hazard group 2; HHP1–HHP2 to extra hazard group 1; HHP3–HHP4 to extra hazard group 2. NFPA uses a density-area curve, so a line is read rather than a single point; EN 12845 gives a fixed density and fixed area directly, which speeds the calculation.

Turkish context

BYKHY ties sprinkler design to TS EN 12845 or NFPA 13. Because insurers on Turkish projects generally work with EN 12845 and the European approval bodies, the classification tables are the daily language on site. Municipal and fire service approval frequently requires the facility-to-class match to be presented with a written justification; citing the annex entry with its clause and table number speeds the exchange. For unlisted facilities, adding a line noting that the annex serves as guidance, and attaching the fire load calculation and the insurer's opinion, is standard practice.

Frequently asked questions

Is the classification annex binding?

Although normative, its tables are a minimum classification list and also serve as guidance for facilities not named. The list is not closed; it is interpreted in agreement with the authority and the insurer.

Schools and offices appear under both LH and OH1 — which applies?

They match conditionally under the classification clause. With low fire load, small compartments and limited combustible content, LH applies; otherwise OH1. Most modern schools and open-plan offices fall into OH1.

My facility is not on the list — what now?

Take the nearest comparable facility and run a risk assessment covering fire load, process temperature, quantity stored and the presence of flammable liquids. Record the decision in writing with the authority and the insurer.

What is the difference between the classification and commodity annexes?

The classification annex links a facility type to a hazard class; the commodity annex places stored goods in Categories I–IV. Both operate in a shared area, and the higher value governs.

What happens where a spray booth sits within an OH1 area?

The note is explicit: a high fire load area within an OH1 or OH2 occupancy is treated as OH3. The whole facility need not be upgraded, but where the areas are openly connected the higher density governs.

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