One of the most common issues that I find, when doing home inspections in Bellingham and Whatcom County, is the B-vent from the furnace, the water heater or the gas fireplace buried in attic insulation. Even though the B-vent is designed to reduce the spacing required for proper combustible clearance, it requires at least an inch of clearance to flammables and that includes insulation.
The temperature of a B-vent, if it is against wood, can lead to pyrolysis (lowers the combustion point of wood) or a fire. As I said, normally the inspector sees insulation around the B-vent. A metal shield or collar can take care of that. But sometimes the vent is improperly installed and it rests in direct contact with wood. That, too, is a problem and someone needs to get up there and do the job right. A fire hazard is not something you want to have brewing up in the attic.