Why is it important to consider the reaction of fixings in a fire?

Mechanical installations above escape routes and emergency exits

It is not uncommon for mechanical installations to be fitted above escape routes and emergency exits. If there is a fire rated suspended ceiling below the installations, there are certain criteria to be considered for the fixing products used to ensure they do not fail in the event of a fire, potentially blocking the escape route.

Regulations for cable fixing are slightly different and are covered in the 18th Edition IET Wiring Regulations. You can find a summary regarding cable fixing requirements here.

Two factors to consider: deformation and fire resistance

There are two things that are tested with regard to fire rated fixings:

• Deformation – this is how much the pipe support (strut/rail, clamp, rod etc) is going to deform under fire conditions (measured in mm)
• Fire Resistance – this refers to how much load the support can take related to the duration of the fire

Deformation

The impact of deformation can be seen in the images below. The first picture shows how a piece of channel will behave in a fire. Essentially the steel will become elongated downwards in the heat.

The second picture shows how a typical pipe clamp fixed with a threaded rod will also be elongated and deformed, and potentially break through any suspended ceiling underneath it.

Correct design should take into consideration the elongation of both strut channel and pipe clamps in order to determine the minimum distance required from the suspended ceiling.

Fire resistance of fixings

The length and heat of a fire can lead to a reduction in load bearing capacity of pipe fixings. The longer a fire burns, the more the load bearing capacity of the fixings will be reduced. Therefore the safe distance between pipe supports on a fire-rated installation will be much less than on a non-fire rated installation.

The diagram below illustrates how much closer the pipe clamps may need to be placed in order to offer a fire rating (F) of 30, 60 or 90m minutes.

It is important to consider the deformation and fire resistance of all components making up the fixing system in a fire rated installation including anchors, threaded rod, channel, pipe clamps and any other fixing elements being used.

Get in touch with us if you have any questions about fire tested fixings or to discuss a current project and will we do what we can to help you.