Fire Resistance

The combustion of wood can be inhibited chemically with the so-called fire retardant. The agents affect properties such as time to ignition, flame spread, and heat and smoke. Fire retardant is mainly important for the early course of the fire, which is the time to flashover of a room. The time to flashover can thus be extended. In some cases, flashover completely prevented. Fire retardants can be added by impregnating or coating with a color. The most common fire coatings swell up to fire and thereby isolate the wood. Impregnating often gives a more lasting and durable protection.

Fire retardants

Traditional fire retardants are inorganic, water-soluble salts, such as phosphates, borates and sulfates. They should not be used outdoors or in damp conditions.

Resistance of fire-resistant wood

It is relatively easy to achieve top class finishes for wood, for example by impregnation with fire retardant. The difficulty is that, while maintaining the other excellent properties of wood. There is a need generally large addition amounts, often 10-20 weight percent, to achieve sufficient fire protection, which contributes to other properties may be affected. The additives are often water soluble and hygroscopic and therefore have a tendency to absorb moisture and to migrate at different humidity. This can cause high moisture content in fire-resistant wood and efflorescence on the surface of the wood. Indoors, this is mainly an aesthetic problem, but outdoors fire effect can disappear by fire retardant leach out.

A Nordic monitoring system for the resistance of fire-resistant wood has therefore been developed. It is based on initial testing of fire and resistance properties with follow-up inspection after certain time intervals.

Fire-retardant wood are classified according to the new system in three utility classes with regard to the intended use. All types shall meet the existing requirements for fire performance.

Fire Protected wood is primarily recommended for indoor use, that is in use class I. Outdoor use is generally required that the fire retardant wood paneling is finished with both basic and top coating.

There are also paints and varnishes that can provide high class finishes. They may be less abrasion resistant than standard colors, and is therefore most suitable for use such as ceilings. These finishes are in the lists of approved products and are intended for indoor use.


 
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