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Consulting Engineer

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  • Comment on: News analysis: Five questions about Grenfell Tower that must be answered

    Consulting Engineer's comment 20 June, 2017 8:46 pm

    Fire alarm provision is a subject often discussed incorrectly in the media, if I could provide some clarity as a designer.

    Residential buildings require different fire alarm solutions to commercial buildings. Whilst it may be acceptable to evacuate a commercial building even if the alarm is false, evacuating hundreds of people in the middle of the night every single time someone burns a piece of toast would not be. Particularly within a high rise where upon fire alarm activation the lifts are programmed to be locked out of public use, evacuating hundreds of occupants many of them elderly or infirm down 22 flights of stairs would be extremely hazardous.

    As a result the fire alarms are configured in MOST residential high rise developments to alarm only with the affected apartment and for other residents to remain within their own apartment . The 1hr fire compartment around the affected apartment should provide sufficient time for the alarm to be raised, the fire service to locate the fire and either extinguish it or under extreme circumstances carry out a controlled and phased evacuation of the building.

    There are around 1,000 tower block fires in London alone and in 999 instances the 'Stay Put' policy works perfectly, protecting the occupants and allowing the fire service unrestricted access to locate the fire with damage limited usually to one apartment. This certainly would not be the case if the fire service also had to deal with the chaos of hundreds of residents blocking the corridors and single escape stair delaying them access.

    However for this solution to work, it is imperative that the spread of fire between compartments is controlled. Unfortunately this was not the case at Grenfell Tower and identifying why should be the immediate focus of investigators.

    It is also important to note that sprinklers fitted within a residential development (domestic sprinklers) are very different to those fitted within a commercial building and offer much lower performance and capacity. Simultaneous fires in a large number of apartments such as here caused by spread of fire externally would quickly overwhelm a domestic sprinkler system.

    Domestic sprinkler systems rely on the buildings general cold water pipework, pumps and pressure to deliver some water to a fire. A commercial sprinkler system has dedicated water supply & pipework, massively powerful pumps and backup power supplies and would be incredibly difficult, time consuming and expensive to retrofit into an existing tower.

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