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Why is concrete fire resistant?


Framing Your Home: How does Concrete Hold Up?
Most engineers agree that the fire performance of the WTC buildings on September 11th was impressive, because the compartmentalization of heat and flames gave thousands of people a chance to escape before the buildings fell.
Most engineers agree that the fire performance of the WTC buildings on September 11th was impressive, because the compartmentalization of heat and flames gave thousands of people a chance to escape before the buildings fell.
Spencer Platt/Getty Images

If you're fortunate enough to have something to say about the choice of framing material in your home, you might consider concrete over wood. Homebuilders have been turning to concrete as a framing material in recent years for a variety of reasons, not the least of which is its fire resistant properties.

Concrete is generally considered to be a good value in home building when it comes to fire performance, as it holds up much better than wood in intense heat [source: The Concrete Center]. This is partly because concrete allows for compartmentalization (i.e. containment) of fire. For an example of compartmentalization, let's take a look at the burning of the World Trade Center (WTC) Towers on Sept. 11, 2001.

Despite the intense heat of burning jet fuel when the planes hit the WTC buildings on that fateful September morning, the 4-inch (10-centimeter) concrete slabs between each floor of the towers were able to limit the spread of the fire, at least for a while. However, the tower walls were framed in steel and other materials, not concrete. As the heat of the fire topped 800 degrees Fahrenheit (427 degrees Celsius), the tower's supporting steel structures weakened and began to collapse [source: Scientific American]. Still, most engineers agree that the fire performance of the WTC buildings on Sept. 11th was impressive, mainly because the compartmentalization of heat and flames gave thousands of people a chance to escape before the buildings fell.

As a building material, concrete also stands up well in the face of other hazards such as hurricanes, tornadoes, and floods, and provides better soundproofing and energy efficiency than wood [source: International Association of Certified Home Inspectors]. However, despite these qualities, it does have some drawbacks. One is its significant carbon footprint. Generally speaking, for every ton of concrete produced, there is a ton of CO2 released into the atmosphere [source: Chemistry World]. The carbon footprint of other materials (for instance, steel) may be the same or worse, but since there is much more use of concrete in the world, the footprint seems bigger. Concrete factories are becoming more efficient all the time, but there is no denying this material's enormous environmental impact.

Nevertheless, if concrete is so fire-resistant, why is it not used in all homes? We'll explore that in the next section.


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