What is the maximum flame spread index allowed for thermal and sound insulating materials?

The maximum flame spread index allowed for thermal and sound insulating materials is set at 25 to ensure safety in building construction and occupancy. The flame spread index is a measure of how quickly flames will spread across the surface of a material when exposed to a fire. Materials with a flame spread index of 25 or lower are considered to have excellent fire-resistant properties and are more suitable for use in buildings, as they can significantly reduce the risk of fire spread, thereby enhancing occupant safety.

Materials that exceed this index, whether options B, C, or D, indicate a higher level of flame spread and consequently pose a greater risk during a fire situation. The limitation to a maximum index of 25 helps maintain strict fire safety standards, especially in commercial buildings where large numbers of people may occupy the space. This encourages the use of materials that will not contribute excessively to fire growth, allowing for safer evacuation and more time for emergency response.