Cellulose Insulation - Part 2

The critical radiant flux test for cellulose insulation “measures the critical radiant flux at the point at which the flame advances the farthest. It provides a basis for estimating one aspect of fire exposure behavior for exposed attic floor insulation.” The smoldering combustion test “determines the resistance of the insulation to smolder under specific laboratory conditions.” This test is conducted utilizing a lit natural tobacco cigarette with a typical heat output of 4 to 6 watts, lit end upward, in an open, snug fitting cavity within a sample of cellulose insulation. Combined, these tests provide a measure of cellulose insulation’s resistance to flaming combustion at specific levels of radiant heat flux and ignition by a cigarette in specific laboratory environments. To meet these ASTM specifications, manufacturers of cellulose insulation commonly apply borax and boric acid in a dry powder form. The borax works to retard flaming ignition and flame spread while the boric acid lessens the smoldering potential. However, studies have shown that, regardless of amounts present, the boric acid will only reduce the speed of smoldering and not prevent smoldering from initiating. The insulation may well be compliant to all applicable standards and still be ignited and smolder.