Five years after I installed these hoods, I happened to be in the area and stopped in to talk with the supervisors of this plant. It turns out one of the hoods caught fire. An employee was driving in after dark and he was sure that a dragon had landed on the roof and was breathing fire into the stratosphere. They were complaining about the only damage that they immediately needed to fix which was the fabric sock between the duct and blower on the roof. I asked them if the roof caught on fire which is what normally happens. Flat roofs on northern die cast plants have 3 inches of foam insulation under a rubber membrane. I said good. The fiberglass insulation without paper around the duct at the roof penetration worked as planned. I asked if the duct pipe fell down. No but it bent a little when it turned orange hot. I said good, the slip joint just below the roof let the duct grow as it got hot. They admitted that they thought I was crazy when I enforced these protective design measures during installation.