Fire protective boards as a system

What the lining does

The danger for a thin-walled section is rapid heating. The job of the lining is to buy time: to hold the heat back so that the steel behind it reaches the temperature at which it fails later.

This protection therefore does not come from the material being non-combustible but from slowing heat transfer. That is why the thickness, density and number of layers matter — and whether the board stays in place during the fire.

Why fixing is the critical point

A fire resisting board protects only while it is up there. During heating the board shrinks, may crack and may tear around the screws. That is why the tested system specifies not only which board is on the wall but also which screws, at what spacing, with what joint detail — and these cannot be departed from.

This is what is breached most often in practice: the board is right, the screw spacing is not, the joint does not fall where it fell in the tested arrangement. In that case the verification obtained for the system does not apply to the wall as built.

What the board’s datasheet says — and what it does not

The board’s declaration of performance certifies the characteristics of the product: reaction to fire class, density, strength. It cannot certify a fire resistance rating on its own, because that is not a product characteristic.

Boards that can be considered fire resisting without a system do exist, but they are very expensive and are rarely the economical solution.

System verification for a load-bearing wall

Here is the key point: there is no off-the-shelf system certificate for a load-bearing light gauge steel wall — it has to be obtained. There are two routes:

• a technical assessment (national or European) in which the tested build-up and detailing are recorded, or
• project-specific, signed fire design or simulation.

In detail: when no system document is required and fire simulation.

The point

A fire resisting board is not a solution but a component of one. What has to be verified is the build-up — board, frame, fixings and junctions together.