What is a Fire Rating?
A fire rating refers to the length of time that a material can withstand complete combustion during a a standard fire rating test. Fire testing of building materials and components of buildings -- such as joists, beams and fire walls -- is required in most places by building codes. Other fire tests for things such as appliances and furniture are voluntary, ordered by manufacturers to use in their advertising. Wall and floor safes are examples of products for which fire resistance is a key selling point.
With the required tests, the results are measured in either units of time, because the emphasis is on holding up under fire (literally) long enough for the occupants of a home or building to escape, or by classification designations. This does not mean, necessarily, that the components of every new structure have to be fire tested. In most cases, the fire rating has been already established by testing the product before it is even put on the market. Moreover, it behooves contractors to be aware of the fire rating of the materials they plan to use on a project before they are put into place.
Nevertheless, the information generated by fire ratings is always changing. The interior and exteriors of the World Trade Center towers were given a high fire rating when tested against traditional fire sources. It was only when an unexpected accelerant -- jet fuel -- was introduced that the steel beams melted and the structure collapsed. From that wreckage emerged yet another footnote to the fire rating scale.
Different governmental entities around the world can hold buildings to greater or lesser standards, although there is generally a consensus on standard materials. Sometimes, a fire rating depends upon circumstances. The fire rating used for vehicular tunnels is unusually high, for instance, because the consequences of a conflagration inside such a tunnel would be especially disastrous.
The National Protection Association promotes the improvement of fire protection and safety through testing, but the tests themselves are generally conducted by private companies not connected to the manufacturers or builders. Should a building receive an unsatisfactory rating, the contractors might be required to thicken a firewall, or perhaps install a sprinkler system in the ceiling. Most building codes require a one or two-hour fire rating for walls in commercial buildings.
Written by Darrell Laurant
