The LWF Blog
Fire Engineering Design and Risk Assessment – Sprinkler Heads – Part 20
November 9, 2017 3:08 pmIn LWF’s recent Fire Engineering Design and Risk Assessment blogs for Architects and others in the building design industry, we have been looking at sprinkler systems. In Part 19, the potential for issues relating to concealed pattern sprinkler heads was explored and in Part 20, we will talk about the role of sprinklers in buildings for life safety purposes.
The Building Regulations (2010) contain the minimum standards for design, construction and alterations for buildings in England and Wales. Approved Documents are provided which set out the requirements clearly and give practical guidance on how to achieve compliance. Approved Document B relates to fire safety and so includes sprinkler provision. It states that the inclusion of sprinklers which adhere to BS EN 12845 (2015), with the additional requirements for life safety, allows for certain concessions to design criteria.
These may be as follows:
– Compartment sizes may be increased
– Duration of fire resistance may be reduced
– Mechanical extraction may be used in basements, instead of natural ventilation
– The number of firefighting shafts may be reduced
– Space separation between adjacent buildings may be reduced.
The concessions listed will not impact upon means of escape provision and the slower reaction to a fire which is expected of concealed pattern sprinkler heads should not negatively impact means of escape, unless:
– The fire size within a larger than usual compartment could reach an intensity which would threaten the fire-resistant structure prior to actuation of the concealed pattern sprinklers.
– That a fire within the building could grow to a sufficient size to threaten neighbouring buildings prior to the concealed pattern sprinkler becoming active.
– The structural fire-resistance of the building could be threatened before the concealed pattern sprinkler activated.
Where a building is more than 30 metres in height and phased evacuation is in place, sprinklers are a requirement. In the UK, buildings of this height must contain sprinkler provision, but the number of escape stairs, travel distances and the type of protection provided to the stairways cannot be reduced when sprinklers are installed. Means of escape criteria, in this case, are met by achieving the correct stair location and travel distance.
Fire Engineered methods involving sprinklers to achieve fire safety equivalence in building design tend to result in longer travel distances and fewer stairs. Examples of such designs can be seen in various countries around the world, but most commonly in the US. In the UK, design plans must be substantiated with relevant calculations to support the case and increasingly, these calculations refer not to travel distance, but to available safe egress time (ASET) and required safe egress time (RSET), the assessment being a comparative of the two.
To ensure the suitability of the fire engineered method including sprinklers, it must be shown that the reaction time of the sprinklers is determined against fire growth and rate of smoke production expectation, given the combustible materials and load within the space. To achieve this, it may be that a closed room test is undertaken to measure the reaction time of the sprinklers against a known fire size.
In Part 21, we will begin by looking at other devices which might be encountered in a fire engineered design including sprinklers. 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.