6.2.3.4.

(1) Coverings, linings and associated adhesives and insulation of air ducts, plenums and other parts of air duct systems shall be of noncombustible material when exposed to heated air or radiation from heat sources that would result in the exposed surface exceeding a temperature of 120°C.

(2) When combustible coverings and linings, including associated adhesives and insulation, are used, they shall have a flame-spread rating of not more than 25 on any exposed surface or any surface that would be exposed by cutting through the material in any direction, and a smoke developed classification of not more than 50, except that the outer covering of ducts, plenums and other parts of air duct systems used within an assembly of combustible construction may have an exposed surface flame-spread rating of not more than 75 and may have a smoke developed classification greater than 50.

(3) Combustible coverings and linings in Sentence (2) shall not flame, glow, smoulder or smoke when tested in accordance with the method of test in ASTM C411, “Hot-Surface Performance of High-Temperature Thermal Insulation” at the maximum temperature to which the coverings and linings are to be exposed in service.

(4) Except as provided in Sentence (5), foamed plastic insulation shall not be used as part of an air duct or for insulating an air duct.

(5) Foamed plastic insulation may be used in a ceiling space that acts as a return air plenum provided the foamed plastic insulation is protected from exposure to the plenum in accordance with Article 3.1.5.12.

(6) Combustible coverings and linings of ducts, including associated adhesives and insulation, shall be interrupted at the immediate area of operation of heat sources in a duct system, such as electric resistance heaters or fuel-burning heaters or furnaces, and where the duct penetrates a fire separation.

(7) Linings of ducts shall be installed so that they will not interfere with the operation of volume or balancing dampers, fire dampers, fire stop flaps and other closures.

(1) Coverings, linings and associated adhesives and insulation of air ducts, plenums and other parts of air duct systems shall be of noncombustible material when exposed to heated air or radiation from heat sources that would result in the exposed surface exceeding a temperature of 120°C.

(2) When combustible coverings and linings, including associated adhesives and insulation, are used, they shall have a flame-spread rating of not more than 25 on any exposed surface or any surface that would be exposed by cutting through the material in any direction, and a smoke developed classification of not more than 50, except that the outer covering of ducts, plenums and other parts of air duct systems used within an assembly of combustible construction may have an exposed surface flame-spread rating of not more than 75 and may have a smoke developed classification greater than 50.

(3) Combustible coverings and linings in Sentence (2) shall not flame, glow, smoulder or smoke when tested in accordance with the method of test in ASTM C411, “Hot-Surface Performance of High-Temperature Thermal Insulation” at the maximum temperature to which the coverings and linings are to be exposed in service.

(4) Except as provided in Sentence (5), foamed plastic insulation shall not be used as part of an air duct or for insulating an air duct.

(5) Foamed plastic insulation may be used in a ceiling space that acts as a return air plenum provided the foamed plastic insulation is protected from exposure to the plenum in accordance with Article 3.1.5.12.

(6) Combustible coverings and linings of ducts, including associated adhesives and insulation, shall be interrupted at the immediate area of operation of heat sources in a duct system, such as electric resistance heaters or fuel-burning heaters or furnaces, and where the duct penetrates a fire separation.

(7) Linings of ducts shall be installed so that they will not interfere with the operation of volume or balancing dampers, fire dampers, fire stop flaps and other closures.