As a firefighter I saw too many fires involving cellulose insulation. The stuff is supposedly treated to make it fire retardant. Back in the 70's we had a facility in an industrial park in the city I served that ground up newspaper, treated it and packaged it. A couple of times we responded to smoldering fires in the trailers where the finished product was packed and ready for shipping. That was the fresh stuff. The city I worked in had thousands of three story, balloon wood frame dwellings. Most were built in the late 1800s and early 1900s. Gas lighting was replaced with knob & tube and then metal sheathed "bx" wiring. The lack of an adequate ground wire can heat up the metal sheathing red hot like toaster wires. Cellulose insulation blown into the walls and ceilings around the bx cables became the first item ignited in too many fires. I tried to get the stuff banned, but it's too big an industry.
