The ease of ignition, speed of flame spread and length of time a material will maintain its structural integrity are all elements that must be considered in choosing a material for constructing a more fire safe home. These same elements are rarely considered when an architect or contractor is planning a home.
Comparative effects of fire on various materials
Fire is the largest single cause of destruction of buildings and the materials from which they are constructed. Some materials gradually lose their cross-section by burning, some soften and lose strength, and others crumble when exposed to high temperatures. Such temperatures occur during all building fires, and frequently exceed 1,000°F within a few minutes after the fire has started.
Let’s compare what happens. At a temperature of 150°F, usually reached within (5)-minutes, structural building materials will not be ignited but beyond this temperature, human evacuation will be impeded. Before this temperature is reached, smoke from burning contents usually makes the building uninhabitable.
At 572°F, most aluminum alloys are reduced to half their strength and melt at about 1,112°F. Steel has a little less than half its breaking strength at 1,022°F, and loses 90% of its structural strength at 1,382°F.
Ordinary untreated wood does not begin to burn until a temperature of 523°F is reached, and fire retardant treated wood will only begin to char. Wood loses its strength in a different way than metals. In the early stages of a fire, it is quite likely that its unit strength is increased because of reduced moisture content. Wood is a good insulator and does not transfer the heat on its surface to its core very quickly. While it may be burning or charring on its surface, its interior will be relatively cool for a long time. All this increases the length of time wood and fire retardant treated wood will retain its integrity – time to get the people out of the building, time to get the firemen to the building and time to extinguish the fire. Fire retardant treated wood has the added advantage of maintaining structural integrity even longer because it chars at a slower rate than untreated wood is consumed. In addition, fire retardant treated wood will not spread the fire from one portion of a building to another, and it will extinguish itself once the ignition source is removed.