Class 1 uninsulated flexible duct constructed of polymer material, helical wire, fire resistant barrier material, and flame resistant yarn and method of use

An uninsulated flexible duct comprising:

• a duct wall, the duct wall having an outer surface and an inner surface, the duct wall forming a channel for fluid flow therethrough, the duct wall including a helical wire;
• a fire resistant barrier material forming a part of the duct wall, the fire resistant barrier material including an overlap zone, wherein a first surface of the fire resistant barrier material faces a second surface of the fire resistant barrier material, the first and second surface of the overlap zone bonded together, the overlap zone running along a length of the uninsulated flexible duct;
• and
• a flame resistant yarn adhered to an outer surface of the duct in a path that crosses or at least partially covers the overlap zone or in a path wherein the yarn is centrally positioned between adjacent helical wires so that the yarn would be generally aligned with a weight placed between helical wires in a flame penetration test.