The LWF Blog
Fire Engineering Design and Risk Assessment – Firefighting & External Water Supplies – Part 29
February 25, 2019 12:44 pmIn LWF’s fire engineering blog series for Architects and others in the building design business, we have been talking about firefighting and those provisions which should be made to support the Fire Service upon their attendance at a building to deal with a fire. In part 28, we looked at how some publications and groups have approached the subject of sufficient water provision for a fire. In part 29, we will continue from that point.
One alternative method of working out the required flow rate of a hydrant is given in Fire Service Manual Volume 1 and assumes an average hose line of four or five lengths, providing the following flows as an estimate:
45 mm diameter hose – 300 litres/minute
70 mm diameter hose – 600 litres/minute
90 mm diameter hose – 1200 litres/minute
The Building Disaster Assessment Group (BDAG) was set up by the office of the Deputy Prime Minister following the terrorist attacks on September 11th in the U.S. It was asked to consider issues related to firefighting in buildings. A report issued by the BDAG in 2004 looked at compartment firefighting in high-rise buildings and one of the conclusions stated:
‘A minimum running pressure of 4 bar and a maximum of 5 bar should be maintained at each landing valve when any number, up to three, are fully opened with a flow rate of 500 litres/minute [i.e. a total of 15000 litres/minute].’
BS 9999:2017 – Fire safety in the design, management and use of buildings. Code of practice. puts forward a general recommendation with regards to hydrants, stating that ‘hydrants should be capable of delivering a sufficient flow of water to enable effective firefighting to be undertaken’. This standard is the one that should be applied to planning water supplies for new buildings. BS 9999 was produced after Approved Document B and so is not referred to in ADB.
While there are various ways to approach the calculation of recommended flow rates, it would seem that the most research was undertaken to support their theory by the BDAG. If their conclusions are accurate and relate to water pressure and flow requirements for a high-level compartment, it seems likely that those figures will be sufficient for all compartment fires. Unfortunately, the majority of the work undertaken by the BDAG does not seem to be currently available online.
As there is no requirement of British water companies to provide a minimum flow rate for firefighting purposes, it may fall to the developer to enhance the flow rate in some cases.
In part 30 of this series, LWF will begin to look at the potential for additional external water supplies other than hydrants. 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.