2-1.1 exc. no 3 Vibration isolation connectors in duct system shall be made of an approved flame retardant fabric or shall consist of sleeve joints with packing of approved non-combustible material. Vibration isolation connectors constructed of fabric shall not exceed 10 inches in length. – NFPA No. 90B 1980.
2-1.2-3 Vibration isolation connectors in duct systems shall be made of an approved flame retardant fabric or shall consist of sleeve joints with packing of approved material having a flame spread rating of not over 25 and a smoke development rating of not over 50. Vibration isolation connectors constructed of fabric shall not exceed 10 inches in length. – NFPA No. 90A 1981.
