The LWF Blog

Passive fire protection for Building Professionals – Part 20

August 5, 2020 2:06 pm

In LWFs blog series on passive fire protection for building professionals and contractors and those with an interest in structural fire protection issues, we aim to give an overview of the important role passive protection plays in the overall fire safety provision of a building. In part 19, LWF began to discuss ducting, an important area in the provision of passive fire protection to a building. In part 20, we will continue looking at fire dampers for ducting and how to choose the correct type of damper for the environment.

Thermally-activated dampers are a type of damper which may be intumescent and fitted to ducting. They simply take the form of a grille filled with a chemical material which expands when heated. These are not commonly used, as they will not prevent the spread of smoke in the early stages of a fire (i.e., before the heat has become sufficient for the chemical material to react).

A smoke-activated damper is designed to prevent the spread of smoke and fire. These are fitted to the ducting and are activated by connection to the smoke detection system. Smoke detectors in other rooms may trigger the alarm and therefore the damper, or they may have in-line detectors fitted inside the ducting itself.

In-line smoke activated dampers are often inaccessible and are therefore poorly maintained and can be prone to false alarms in the event of humidity or dust travelling through the ducting.

Sometimes other methods are used to protect ducting and prevent fire spread. This may include constructing the ducting from fire rated materials or enclosing ducting in specialised construction. Fire-rated ducting provides protection by the ducting itself being constructed from fire-rated materials which will withstand the effects of a fire. The ducting, in effect, becomes its own fire compartment and fire is unable to break into or out of the ducting.

The effective ducting compartment would usually start at the point the ducting originates, in a room, and continue to the point at which the ducting leaves the building and passes into a safe compartment/area. This means that if there is a fire in a room through which the ducting passes, the fire cannot enter the ducting and s[red to neighbouring rooms.

Where such ducting protection is put into place, it is common practice to fit a fire damper at the point of access to the ducting, i.e., in line with a fire-rated ceiling or similar.

In part 21 of this series, LWF will continue looking at the types of fire protection afforded to ducting, before looking at glass and glazing in fire-rated construction. 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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