Reaction to fire.
Fire owes its existence to three basic elements, these being combustible material, oxygen and heat. Protective systems that increase the fire resistance-rating act in two different ways.
- By producing a protective foam that insulates the wood from the source of heat/flame, thus eliminating contact with the combustible material (intumescence).
- By employing substances that inhibit the oxygen supply (fire-retardant).
The choice of products to be used depends on the field of application of the wooden element to be treated.
- For wooden flooring, the fire-reaction rating is favourable because flame and heat tend to rise upward. In addition to the specific fire-reaction properties, parameters linked to resistance to abrasion and staining are also required for flooring. These parameters do not influence behaviour in fire but they are clearly essential for a suitable coating for flooring. Amonn offers Amotherm Wood Hydrolac WB, a water-based coating and Amotherm Wood 540 SB, a solvent-based coating.
- If the product is to be used on wooden wall and ceiling coverings, no particular properties other than the specific fire-reaction rating are required. Obviously ease of application is an advantage for structures already in situ. Amonn offers Amotherm Wood WSB, a transparent varnish and Amotherm Wood WB together with the finishing coating Amotherm Wood Top WB, coloured varnishes.
- If the product is to be used on wooden furniture and fittings and in industrial environments, the aesthetic quality required is undoubtedly as important as the fire-reaction certification. Amonn offers Amotherm Wood 450 SB, a transparent polyurethane varnish and Amotherm Wood 451 SB, a coloured polyurethane varnish, both of which are available in different degrees of gloss and with specific catalysers for different fields of industrial application.
Resistance to fire.
The speed at which the wood carbonises is an important factor that has always been used in the design of fire-resistant structures, increasing the section of the wood. The Eurocodes define and set the standards for the carbonisation speed of different types of wood. If we take pine as an example, this is said to have a speed of 0.8 mm/min, while this reduces to 0.7 mm/min for pine laminate. For a wooden roof in pine laminate an hour after exposure to fire the section of a beam will be reduced by 42mm (0.7mm/min x 60min) on each side exposed to fire. If the load-bearing capacity of the residual section is still sufficient to support the structural loads, the structure is certified with a fire-resistance rating of R60. If the section is unable to bear the load, different solutions can be used: mix the panels with expendable wood or use reactive protection systems that do not alter the size and aesthetics of the structure.
Oversizing the structure is undoubtedly the simplest option, also preferable from the architectural point of view, since this does not require the addition of protective systems but it does have some major limitations.
- It is a solution that can only be applied pre-construction, at the planning/design stage.
- For structures in solid wood it is linked to the size of the trees producing the timber.
- Enough space must be available, making it impossible in restricted spaces to increase the size of load-bearing structures.
If oversizing is not possible at the start, or in the event of rebuilding or change of use, fire-retardant /reactive varnishes are the only means of preserving the architectural aesthetics by leaving the wood-graining on view.