Wood and fire

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Fire resistance

Every year in Italy more and more houses are built in wood due to the excellent performance and living qualities that this material offers. Among the most appreciated features is its fire resistance.

Fire resistant? Wasn’t it a combustible material?

To explain ourselves better, it is good to first define what we mean by fire resistance.

The fire resistance of a structure refers to the ability of that structure to maintain its stability, integrity and thermal insulation during a fire. It is about how long a structure can withstand the action of fire before significant damage or structural collapse occurs.

The fire resistance of a structure depends on several factors, including the materials used in its construction, design and thermal insulation.

A structure’s fire resistance is often evaluated through standardized tests, such as laboratory fire resistance tests, which simulate typical fire conditions. These tests measure the structure’s ability to withstand a fire for a specified period of time, commonly expressed in terms of fire resistance in hours.

The fire resistance of the structures is governed by specific rules and regulations which establish minimum requirements to guarantee the safety of the occupants and the protection of the structures themselves.

It is important to emphasize that the fire resistance of a structure does not imply that the structure is completely immune to fire damage. Rather, fire resistance aims to provide a sufficient period of time for the evacuation of the occupants, the intervention of first responders and the control of the fire.

The fire resistance of wood

When we talk about wood, we are talking about a combustible material, which means that it can burn when exposed to high temperatures. The ignition temperature of wood can vary depending on several factors, such as the species of wood, the humidity of the wood, the size and shape of the piece of wood, as well as the intensity of the heat applied. Usually, wood starts burning around 250-300 degrees Celsius (480-570 degrees Fahrenheit).

However, wood has some characteristics that provide some resistance to fire.

Below we list some characteristics that give it a certain resistance to fire. Here are some of the main reasons:

  1. Thermal insulation: Wood is a relatively dense material and has low thermal conductivity. This means that heat travels more slowly through wood than through other materials such as metal. This slows down the spread of flames and limits the rate of fire spread.
  2. Surface Charring: When wood is exposed to intense heat, a layer of charcoal forms on the outer surface. This charring creates a protective barrier which retards the access of fire to the underlying material. Charcoal acts as a thermal insulator, preventing heat from penetrating further into the wood.
  3. Oxygen depletion: During the combustion of wood, the surrounding oxygen is consumed. This can create an oxygen-free zone around burning wood, limiting the amount of combustion that can occur. As a result, the fire can reduce its intensity or go out if there is not enough oxygen available.
  4. Formation of an ash barrier: When wood burns, an ash barrier forms on the surface. This ash acts as an additional insulating layer, protecting the underlying wood from burning.

Other materials such as steel, unlike wood, although it retains its mechanical strength at high temperatures, undergoes a reduction in strength considerably more rapidly due to thermal deformation. In addition, steel and metal have good thermal conductivity, which means they can heat up rapidly during a fire and lose their mechanical strength faster.

Have you understood why wood has excellent fire resistance? Write to us to find out more!

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