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Fire Safety for Facilities Management Personnel – Fire Development – Part 64

September 21, 2020 1:33 pm

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 63, LWF looked at how fire develops inside buildings. In part 64, we consider how the progress of a fire in a building can be divided into phases.

Once a fire starts inside a building, its progress can be divided into three distinct phases: Growth, post-flashover and decay.

The growth period is when the average temperature in the room of fire origin rises relatively slowly.

The post-flashover period, when the temperature is very high and most combustible items in the area are on fire.

The decay period, when most combustible materials have been consumed by the fire and it continues to burn until there is no more fuel for combustion, with the average temperature in the area in decline.

The escape of any persons in the compartment must be made during the growth period and well before flashover. The provision of means of escape to ensure the speedy evacuation of people on the premises is necessary.

When the fire is in post-flashover phase, all elements of the construction are put under stress and it is here that structural fire protection becomes of greater significance. Prior to the structure of the building being under threat, the spread of fire and smoke can be greatly assisted by open doors, poorly-stopped service penetrations and structural features such as service shafts and risers. Effective fire-stopping is essential to avoid the spread of smoke and potentially fire from one floor to another or from one compartment to another by convection.

It should be noted that ventilation and air-conditioning systems can also provide routes for the spread of smoke, combustion products and fire.

Fire-resisting construction is the most fundamental means of protecting escape routes and preventing fire spread. Fire resistance is defined by BS 4422,  as, “The ability of an item to fulfil for a stated period of time the required fire stability and/or integrity and/or thermal insulation and/or other expected duty specified in a standard fire resistance test’.

We can understand from the definition that fire resistance is ascertained in terms of a standard test, that units of fire resistance relate to units of time and that fire resistance may relate to one or all of at least three performance parameters – stability, integrity, insulation or other.

In part 65, LWF will continue to discuss fire resistance. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

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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