Materials used in plenums shall have a flame rating of ____________.

Materials used in plenums shall have a flame rating of ____________.

• A. 15
• B. 25
• C. 20
• D. 30

Answer: (B)

Materials used in plenums must resist flame spread along surfaces, because plenums are air-handling spaces where a fire can quickly travel through ducts and over ceilings if the materials burn or allow flames to spread. Setting a flame-spread rating limit keeps the fire from propagating rapidly through the entire HVAC system, giving more time for containment and occupant safety. The standard limit used in many codes for materials in plenums is a flame-spread rating of 25 or less, measured by tests that assess how quickly flames travel across a material’s surface. A higher rating, like 30, would permit more rapid flame propagation, while lower ratings like 15 or 20 are more restrictive than the code requires. That’s why 25 is the correct requirement.

Materials used in plenums must resist flame spread along surfaces, because plenums are air-handling spaces where a fire can quickly travel through ducts and over ceilings if the materials burn or allow flames to spread. Setting a flame-spread rating limit keeps the fire from propagating rapidly through the entire HVAC system, giving more time for containment and occupant safety. The standard limit used in many codes for materials in plenums is a flame-spread rating of 25 or less, measured by tests that assess how quickly flames travel across a material’s surface. A higher rating, like 30, would permit more rapid flame propagation, while lower ratings like 15 or 20 are more restrictive than the code requires. That’s why 25 is the correct requirement.