This standard states Approval requirements for materials which may be used as insulation on the exterior of noncombustible pipes or ducts. If such a material is sufficiently combustible, it may cause a spreading fire along the route of the pipe or duct which it insulates. Mechanical piping systems such as those in heating, ventilating, air conditioning, or refrigeration sometimes need to be insulated for maximum operational efficiency. This standard sets the performance requirements to accurately assess the ability of a material to resist this fire.