A fire rating refers to the length of time that a material can withstand complete combustion during a a standard fire 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 rating of the materials they plan to use on a project before they are put into place.
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 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.