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Wood burning is a complex process in which several stages can be distinguished, from moist wood to open flame. Under normal conditions, wood has a certain moisture amount, which shifts and is evaporated in the process of burning. The border temperature, at which evaporation occurs, is 100°C. In the process of wood burning and pyrolysis, a layer of coal develops on its surface, which partially protects the wood from burning.

In spite of the complexity of the wood burning process, all timber bearing constructions have one very favorable characteristic – they do not lose their bearing capacity under the effect of fire. In the process of burning, timber bearing constructions lose their bearing capacity by the amount of coal layer developing, and thus it is possible to estimate the timber bearing construction bearing capacity. The basic principle of timber construction designing are described in the fifth Eurocodex LVS EN 1995-1;2. Timber constructions do not bend in case of a fire, as it happens with metal constructions upon reaching critical temperature.

There are several possibilities of ensuring wood fire protection. One of the oldest ways of protection is a mixture of lime and clay, which is used to coat the surface of wooden parts. Due to developments in chemistry, various modern wood fire protection products have been created, e.g., various fireproofs. The activity of these fireproofs can manifest itself variously:

• For instance, under the effect of flames, a fireproof may decompose and create inert gases, which retard the process of burning;
• As a result of the burning reaction, the fireproof consumes a large amount of heat and does not let the wood heat up;
• The fireproof forms a coating on the surface of the wood, which transforms into a layer of dry foam under the influence of flames, and retards flame access to the timber surface.

Such fireproofs are applied to the wooden surface by a brush or sprayer.

At present, timber usage in building is quite limited for several reasons, and one of the weightier is the belief about lack of wood fire safety. To dispel this stereotype, our company, in cooperation with "Kokapstrades tehnologijas centrs" and Ltd. "Meza un koksnes produktu petniecibas un attistibas instituts", is organizing educational seminars about the importance of timber in building, which are targeted at a wide audience – from individual builders to professional architects.

Timber is not a non-burning material; however, it is a material with foreseeable fire-spreading properties, which can be taken into account in designing buildings. Moreover, with appropriate finishing materials, the spreading of fire in timber materials can be retarded.

In practice, full-scale testing methods have long been used, which are, of course, very expensive, but do provide the most realistic idea of fire conditions and material characteristics. One such test was carried out in Norway in 1961, and clearly demonstrated timber construction properties in fire conditions. Two similarly loaded beams (metal and solid wood) are placed side by side. The images speak for themselves:

Fire test (Norway, 1961)	After 8 minutes
After 45 minutes

• Foaming substances which emit a large amount of non-combustible gas (e.g. nitrogen, ammonium hydrate, CO2) in heat;
• Cohesive substances, which melt in heat, creating a thick liquid, thereby trapping the emitted gas in bubbles and producing a thick layer of foam;
• An acid source and carbon compound (upon heating, the acid source emits phosphoric acid, which chars the carbon compound, causing the bubble layer to solidify and creating a fire-resistant coating for it; often, the cohesive substance may also serve as the carbon compound).

In the image below – effect of external temperature upon wood, and temperature in wood.