What does the term "flame spread rating" refer to?

The term "flame spread rating" refers to the measure of how quickly a flame spreads over the surface of a material during testing. This rating is crucial in assessing the fire performance of building materials, as it helps determine how a material behaves in the event of a fire.

A material with a lower flame spread rating is considered safer because it indicates that the material will not allow flames to travel rapidly across its surface, which can prevent the escalation of a fire and give occupants more time to evacuate. This measure is often obtained from standardized tests, such as the ASTM E84 test, which involves applying a flame to one end of a specimen and measuring how quickly the flame travels across its surface.

The other options refer to aspects of fire dynamics but do not accurately define flame spread rating. For example, the time for a flame to extinguish or the duration of flame presence do not directly relate to the material's ability to resist fire spread. Similarly, the time for a flame to reach maximum height deals more with flame behavior rather than the material's surface characteristics. Therefore, option B accurately encapsulates the definition of flame spread rating.