A performance based approach to defining and calculating adequate firefighting water using s.8.5 of the design guide BS PD 7974:5:2014 (fire service intervention)

Paul Grimwood*, Iain A. Sanderson

*Corresponding author for this work

    Research output: Contribution to journalArticle

    Abstract

    The determination of firefighting water requirements in large, tall and complex buildings in the UK has largely been based on data retrieved from studies into full-scale test fires, combined with some real fire research undertaken by the Fire Research Station (FRS) from 1955–1970. This scientific research effectively formed the basis for the design and configuration of rising fire mains (stand-pipes) in tall buildings, as well as water storage provisions for town centre and infrastructure planning. The resulting guidance is also applied to individually isolated buildings that are distanced from the nearest available water supply. However, it is suggested the UK has since fallen behind many international standards and codes, where firefighting water provisions are more reflective of modern building design as movable fire loads, compartment dimensions and window (ventilation) sizes have increased over the years.

    There have been recent calls in both the UK and USA for the development of a performance based method of calculating firefighting water requirements for design purposes, based on the quantity of water actually being used effectively by firefighters. The recent publication of BS PD 7974:5:2014 (7974) meets this need in calculating ‘adequate’ and effective firefighting water (s.8.5). The research by Glasgow Caledonian University (GCU) provides a framework upon which the ‘7974’ water strategy evolved and is based on an analysis of 5401 building fires that occurred in the UK from 2009 to 2012, where active firefighting was undertaken across a broad range of occupancies. When used in design, any recommended deviations from the prescriptive codes may achieve some cost/benefit advantages, whilst at the same time providing an improved firefighting water flow density (L/min/m2). It is also worth noting that UK prescriptive building codes do not differentiate between the volume of firefighting water storage required for residential or commercial buildings. Furthermore, reductions in compartment size and fire load, or enhancements to passive/active fire protection, may mean even less storage water is required when using the 7974 strategy compared to current code compliance.

    The GCU research clearly established that the severity of building fires is dependent on the size of compartment in which the fire originates; the containment of fire spread through the provisions of adequate passive or active fire protection; the fire load density and the potential for a fire to reach a fuel controlled burning regime at peak heat release for the compartment at Qmax. It is further demonstrated that the quantity of firefighting water that may be deemed as ‘adequate’ can be presented on a gradient ( Fig. 13), ranging from the lesser amount (L/min) required in residential buildings (low-flow), upwards through offices or commercial mixed use buildings (mid-flow), to industrial and storage facilities (high-flow). This finding is not reflected in current codes. In using the ‘7974’ methodology to calculate adequate firefighting water, simple equations are utilised in this paper for both sprinkler protected and non-sprinklered occupancies. The method can be also be used where either dry or wet rising fire mains (standpipes) are required.

    In referring to past fire case histories it is then demonstrated that fires can travel across large floor plates, with great speed. A spread rate of >20 m2/min may see a fire develop with such velocity and power that any fire service intervention can become compromised from the outset, unless adequate firefighting water provisions are available and effective fire protection measures are in place.
    Original languageEnglish
    Pages (from-to)155–167
    Number of pages13
    JournalFire Safety Journal
    Volume78
    Early online date1 Oct 2015
    DOIs
    Publication statusPublished - Nov 2015

    Keywords

    • fire-fighting water
    • fire-fighting flow-rate
    • rising fire mains
    • standpipe
    • building fire damage
    • fire spread
    • fire hazard analysis
    • fire engineering
    • suppressive capacity
    • fire load
    • intervention
    • office fire
    • firefighting tactics
    • BS 7974

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