Is duct seal an approved seal compound to put inside a seal off fitting.? I was told thatt duct seal is an approved compound. I was on saem job where we have some fuel guys today installing gas pumps on a separate project and I happend to notice them shoving duct seal inside the seal off. I stopped and said I didnt know duct seal was an approved compound for a seal off in a class 1 div2 location. Everyone of those guys said yes. I was hoping to find a code reference as to the type of approved method for this application but cant find it. I am prettty surre its not approved but I also am not certain. The last time I installed seal offs we used Chico with fiber mesh and circuits had to be separated. These guys were just shoving them inside conduit. Just for peace of mind I would like to know a code reference or UL listing duct seal as an approved compound.