Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants
Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants


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Lawrence Webster Forrest
Legion House
Lower Road

Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583

Fire Engineering Design and Risk Assessment - Sprinkler Installation Design - Part 33

Posted by LWF: 12/02/2018 13:22

In LWFs Fire Engineering blog series for Architects and others in the building design industry, we have recently been discussing the design and installation of sprinkler systems in new buildings. In part 32, we looked at how sprinklers can work within atriums and where there is a sloping roof or soffit. In part 33, suspended ceilings and pipework systems will be discussed.

A suspended ceiling is used to lower the ceiling height of a given room or floor and causes a void between the suspended ceiling and the floor above. Any space of depth 0.8m or more requires protection from fire. One reason for this is that building insurers consider voids of this depth and greater to be a potential storage space. 

In some cases, a void which is less than 0.8m may still require protection, where combustible construction or contents are indicated. Such situations will be highlighted as a part of the fire risk assessment which should identify the level of risk involved. Some of the elements to be borne in mind are how combustible the construction materials are and what fuel load might be expected in the void – for example, fan coil units, type and use of duct insulation, cables etc.

When considering the pipework used as part of a sprinkler system, it can be broken down into two main types of design – Tree/terminal systems and gridded systems. 

Tree or terminal systems are recognisable as such because the sprinkler heads are fed by dead-end range pipes which are, in turn, linked to water distribution pipes which lead to the main water distribution pipes. When the system operates, only the range pipes which lead to the operational sprinklers and the related distribution pipes will contain flowing water.

In the case of gridded systems, water is fed to the sprinkler heads via tie pipes, which are provided for by more than one distribution main, which can also be referred to as a track. Such systems may or may not be connected to the main water supply. 

A gridded system is more complex than a tree system, as each sprinkler is fed from more than one direction. This means that during a fire, it is likely that water will flow through all the pipes, instead of only the one feeding the sprinklers in use.

Gridded systems can prove more economical to install as the hydraulic load is spread over a greater number of pipes which are smaller in diameter than in a comparable tree system. They are most commonly found in buildings which are high hazard with large bays and flat or sloping roofs.

In part 24, LWF will take a look at fully hydraulically calculated pipe arrays, now used in preference to pre-calculated pipe sizes. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.

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.

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