An intumescent material in the safe-off area is intended to expand during a fire and fill this gap. The Safing Insulation is cut larger than the opening and compressed into place in addition to mechanical attachment with safing clips. In a fire, the insulation not only remains in place, but it is smokeless and will not burn. Intumescent materials have several hortcomings. First, for an intumescent material to expand it must char.
Intumescent materials generate large amounts of smoke during the charring and expanding process.
Finally, the performance of the intumescents is based on one test and two computer simulations.