Wood, although itself a combustible material, provides considerable resistance to fire when used in proper sizes. Wood also has self-insulating and slow-burning properties. When a fire starts, wood burns first. This charring provides a protective coating to the interior of the wood and prevents it from burning, even at temperatures up to 500°C. At still higher temperatures, under continued exposure, it gives rise to flammable volatile gases from dehydration, which readily catch fire. Additional fire resistance is obtained by treating wood with large amounts of fire retardant chemicals, such as ammonium phosphate and sulfate, borax and boric acid, and zinc chloride, as these chemicals inhibit the rate of temperature rise during a fire. . The following points should be given due consideration to make wooden structures more fire resistant.
Instead of using many small sections for joists and floor beams, thick sections should be used at wide intervals.
The number of corners and exposed surface area should be minimized. All sharp edges should be rounded.
Wood should not be treated with oil paint or varnish, which are liable to catch fire. Instead, wooden ceilings and partitions should be treated with asbestos or ferrous oxide paint if needed.
In multi-storey timber structures, there should be a minimum number of floor openings and multi-storey levels should not be provided with openings. Through the opening A spreads the fire in a vertical direction and behaves like a chimney and induces a draft.
Adequate fire steps or barriers should be provided in floors and walls.
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