The LWF Blog

Fire Safety for Facilities Management Personnel – Sprinkler Installation Design – Part 234

January 8, 2024 12:10 pm

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 233, LWF discussed sprinkler system installations and components. In part 234, we look at sprinkler installation design principles.

When approaching the installation design of a sprinkler system, the occupancies should be divided into three hazard categories, according to the nature of the activities and combustible materials that may be present in the building. They are:

• Light hazard
• Ordinary hazard
• High hazard

The increasing level of hazard is indicative of the anticipated size and rate of development of a fire that might start in that area.

A different density of water discharge will be required depending upon which of the three hazard categories applies. The density of water discharge is expressed in the same way as rain – millimetres per minute.

As a limited number of sprinkler heads would be expected to activate to respond to a fire, each hazard category has a different maximum area of operation (AMAO).

Light hazard sprinkler installations are not commonly seen. Non-industrial occupancies where combustibles are low and the building is sub-divided into spaces of limited size by fire-resisting construction are suitable for light hazard systems. Some examples of buildings that might use a light hazard sprinkler system are areas of hospitals and hotels (which are only rarely sprinklered at all), museums and some office spaces. However, once installed there is very little flexibility for light hazard sprinkler systems and a change like making an area of small offices into one large open plan area could necessitate an upgrade to the sprinkler installation.

In the most hydraulically unfavourable part of the installation, the minimum design density in a light hazard installation should be 2.25 mm/minute with an AMAO of 84 m².

Ordinary and high hazard occupancies are subject to further divisions of classification within BS EN 12845 Fixed firefighting systems. Automatic sprinkler systems. Design, installation and maintenance.

In part 235 of this series, LWF will look at the density of water discharge and assumed maximum area of operation for ordinary and high hazard occupancies, as well as typical occupancy classifications. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 35 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

 

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.