What is the maximum flame spread index for plenum enclosure construction materials exposed to airflow?

The maximum flame spread index for plenum enclosure construction materials exposed to airflow is set at 25. This standard is crucial for ensuring safety in buildings, particularly in spaces like air ducts and plenums where materials can be exposed to high airflow. A flame spread index of 25 means that the material will not spread flame significantly in a way that compromises safety.

Materials that are rated within this index have been tested and categorized based on their surface burning characteristics. A rating of 25 or lower indicates that they have limited flame spread potential, making them appropriate for use in environmental conditions where rapid flame spread could pose a significant risk. Fire codes and building standards emphasize the importance of adhering to these ratings to mitigate fire hazards in enclosed spaces, especially where air circulation may carry flames or smoke quickly.

Other choices represent ratings that exceed the acceptable limit for such applications, highlighting the importance of material selection in maintaining safety standards.