Sprinklerové systémy Shark, a.s. - Fire-Fighting Sprinkler Systems

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EU Sprinkler Systems Legislation (EN 12 845)


BS EN 12845 - Fixed fire fighting systems, Automatic sprinkler systems, Design, installation and maintenance

This European Standard was approved by CEN on 29 November 2002.

Sprinkler systems to EN 12845 are designed to extinguish, or at least control, fires in the early stages of development. In essence a sprinkler system is a network of pipes fed by a water supply via a set of control valves. Sprinkler heads are fitted at specific locations throughout the building and these temperature-operated devices discharge water onto fires in specially designed spray patters. The systems are fitted with alarms, visual and audible, which will be triggered when there is a flow of water in the pipework. For sprinklers to operate successfully the systems need to be designed, installed and maintained to a high standard. EN 12845 provides full details on pipe sizing, sprinkler head placement, water supplies, alarms, valves, pumps, commissioning and maintenance.

The following is a brief run through the content of EN 12845.

Extent of sprinkler protection

Sprinklers should be installed in all areas of the building; although it is permissible to exclude sprinklers in certain locations: e.g. toilets/washrooms of non-combustible materials; enclosed staircases not containing combustible materials.

Hazard classification

Buildings, and their contents, are defined by a number of categories, or hazard classifications.

Light hazard LH

Low fire loads with low combustibility and no single compartment greater than 126m2 with a fire resistance of at least 30mins. Typically: Schools and other educational institutions, offices (certain areas) and prisons. The maximum protected area for LH is 10, 000 m2 per control valve.

Ordinary hazard – which is split into 4 groups

Where combustible materials with a medium fire load and medium combustibility are processed or manufactured. The maximum protected area for OH is 12, 000m2 per control valve.

OH1: Typically: Cement works, sheet metal product factories, abattoirs, dairies, hospitals, hotels, libraries (excluding book stores), restaurants, schools, offices.

OH2: Typically: photographic labs, car workshops, bakeries, breweries, car parks, museums.OH3 and OH4

OH3 and OH4: Typically industrial processes and buildings with a high combustible load.

High hazard

High fire load and high combustibility. High hazard categories are typically storage facilities where racking is used and chemical processes.

Types of sprinkler system

There are a number of different types of sprinkler system: wet, pre-action, dry and alternate. Here we will consider only wet systems, ones in which the pipework is permanently charged with water, which are fully calculated. Wet pipe installations should be considered for buildings where the ambient temp will not allow frost damage and where it will not exceed 95º C. Trace heating of pipework is permissible to provide protection from potential frost damage.

Water supplies

Water supplies need to be capable of providing the required flow rates for the system and should have sufficient capacity to ensure the that the sprinklers can remain in operation for the periods given in the following table.

Hazard classification Operation time
LH30 mins
OH60 mins

Water supplies can be town mains, storage tanks, pressure tanks and inexhaustible sources. For fully calculated systems the minimum water volume required is calculated by multiplying the demand flow by the operation duration.

Hydraulic design

The following table gives water density and areas of coverage for sprinklers required by the Standard.

Hazard Design density, mm/min Area of operation, m 2
Note: The Design density is determined from the water discharged through the sprinklers divided by the area covered by the spray. The Area of operation is the area over which the sprinklers will discharge.

The design for a Light hazard system should be for 2.25mm/min discharge over an area of 84m2. This will be for more than one sprinkler head.

Pipe sizing

Fully calculated systems require all pipe sizing to be done by hydraulic calculation. It is also possible to pipe size using a pre-calculated method, one where some work is done from tabulated information. Pipe friction loses are calculated using the Hazen-Williams formula.

p = (6.05 x 10 5 L Q 1.85 ) / (C 1.85 d 4.87 )

p is the pressure loss, bar
L is the equivalent length of pipes and fittings, m
Q is the flow through the pipe, L/min
d is the internal diameter of the pipe, mm
C is a constant for the pipe material, see table.

Values of C for pipe material:

Pipe material C
cast iron100
mild steel120
stainless steel140

Water velocity shall not exceed 6m/s through valves and 10m/s through any other point in the system. The Standard also gives tables for " equivalent lengths" for fittings and valves.


The Standard requires that all underground pipes should have sufficient corrosion resistance. Above ground pipes, downstream of the control valve, will generally be either steel or copper. All pipework should be easily accessible, not buried in concrete floors. Steel pipework can be screw threaded or welded, welds need to be continuous and the weld should not interfere with the flow of water in the bore of the tube. Copper pipes may be used downstream of any steel piping and shall be joined by either mechanical joints or by hard soldering, using fittings according to EN 1254. The Standard requires that copper tube must be formed into bends off-site. For mixed metal systems precautions need be taken to avoid galvanic corrosion. Copper to steel joints have to be flanged, using stainless steel bolts.

Spacing / location of sprinklers

Sprinkler heads should be install according to suppliers recommendations, these will give an indication as to the area of coverage of a single head. It is important to locate the sprinkler heads away from obstructions and at certain distances from walls and the ceiling level. It is also important to keep a minimum distance between sprinkler heads, generally speaking this will be 2m. For pendant sprinklers, ones which discharge downwards, the maximum area of coverage is 21m2 for LH and 12m2 for OH. For sidewall sprinklers, where the discharge is outward in a half-paraboloid discharge, the maximum area of coverage is 17m2 for LH and 9m2 for OH.


All pipework is to be hydrostatically tested for 2 hours at a pressure of 15bar or 11/2 times max working pressure, whichever is the greater. Faults found in the system must be corrected and the test undertaken again. Regular tests are required weekly and monthly to be carried out by the system user. When the system is completed and tested the installer is required to provide the user with a completion certificate, along with documents detailing the system. This documentation should include notes of any part of the system that does not meet the requirements of the Standard for whatever reason.

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