What is the flame spread index derived from?

The flame spread index is derived from visual measurements of flame propagation. This index is a critical parameter used to evaluate the flammability of materials, specifically how quickly a flame travels across a surface. The evaluation process typically involves standardized tests, such as the ASTM E84 test (also known as the Steiner tunnel test), where a sample material is exposed to a controlled flame. Observers measure the distance the flame travels in a set time frame, which allows for quantifying the speed of flame spread across the material.

This method directly correlates to the behavior of fire on different surfaces in real-world scenarios, making it a reliable indicator of safety and performance. While other factors like temperature change, material weight, and thickness can influence fire behavior and safety, they do not directly contribute to the flame spread index as defined by the visual observations of flame movement.