just looked it up......apparently it's treated heavily to get the fire resistance I was thinking ofI have a very vivid recollection of my dad, a career NPS fire fighter, bringing home a full size truck load of those shingles that had been removed from employe housing, and then using them as fuel for every back yard BBQ and shindig bonfire for the rest of my childhood.
I can tell you from burn scars, cedar trunks will often still exist where most pine and fir trees are just gone