Fire safety

Fire safety

International fire safety statistics show no difference in losses between countries which use wood extensively in construction and those which do not. In North America and Europe, statistics show that people are just as safe in a code-compliant wood frame house as they are in a code-compliant house built of light frame steel, concrete, or masonry.

The limits for fire safety performance of large structural wood members can be readily determined and incorporated into building design. As wood burns in a predictable and controlled manner, it is possible to estimate how much of the crosssection of a structural member will remain unaffected by fire after a specified period of burning.

Dimensions can then be specified to ensure the unaffected part of the cross section has the ability to bear the required load over the specified period. Steel, on the other hand, loses all its load-bearing capacity at temperatures of a fully developed fire.

The controlled charring rate of wood is clearly demonstrated when fire testing for structural glue laminated timber. The charring rate is 0,7mm/min, and the remaining unaffected wood and its load bearing capacity can be easily calculated as a function of time exposed to fire.

Fire safety depends on building assembly performance

In fact, fire safety performance in conventional wood frame construction has little to do with the combustibility of the structural materials. It relates to the finished building assemblies, like walls and roofs, which are actually assessed in the tests.

Wood framed assemblies are finished on the interior with gypsum wall board panels. These have very low combustibility ratings. Cavities are filled with non-combustible, mineral fibre insulation. Testing requires these assemblies to be burned under controlled conditions in fire research laboratories at very high temperatures until they fail structurally. Wood framed structural wall and roof assemblies are required to survive these high temperatures for a minimum of one hour before structural failure.

Moreover, fire life-safety in low and medium density housing of all types has very little relationship with structural failure, but rather the inhalation of toxic smoke and gas long before structural failure. Less than 0,25 per cent of fire fatalities in these buildings are caused by the collapse of roofs, walls, or floors. Non-flammable surface materials, sprinkler systems, and smoke detectors can be used to ensure safety from toxic gases during the early stages of a fire. Codes require that all buildings, including wood, be designed and constructed to provide residents with a fast and easy exit in the event of fire.



Tianjin Fire Research Institute (TFRI) fire test of structural glulam column (in fire test furnace), 2007
TFRI fire test of wood frame wall assembly; thermo-couples attached to gypsum plaster board cladding;
after the test
Gypsum wall board lining fulfilling fire requirements