What is the maximum flame spread index allowed for duct coverings to reduce the spread of fire and smoke?

The maximum flame spread index allowed for duct coverings is significant because it establishes a standard to minimize the risk of fire spreading through the duct system. A flame spread index of 25 or less is typically recognized as a standard that provides an acceptable level of fire safety, making it the threshold for acceptable materials used in these applications.

Materials with a flame spread index of 25 or lower are considered to have limited fire risk, thereby effectively reducing potential hazards associated with fire and smoke in both residential and commercial buildings. Maintaining this standard helps to ensure that, in the event of a fire, the duct system does not contribute significantly to the spread of flames or smoke, enhancing overall safety for occupants and property.

The other indexes suggest higher levels of flame spread, which would increase the potential risk of fire and smoke dissemination, thus not adhering to the safety protocols required by the code.