Smoldering Combustion Hazards of Thermal Insulation Materials. Interim Report. October 1, 1979-April 30, 1981.
Smoldering Combustion Hazards of Thermal Insulation
Materials. Interim Report. October 1, 1979-April 30,
Ohlemiller, T. J.
NBSIR 81-2350; 65 p. August 1981.
Sponsor:Department of Energy, Oak Ridge, TN
Available from: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
1-800-553-6847 or 703-605-6000;
Order number: PB82-107046
boric acid; insulation; ignition; propagation;
The smoldering combustion hazards of cellulosic loose
fill insulation materials fall into three categories:
smolder initiation, smolder propagation and transition
from smoldering into flaming. Our previous findings on
the initiation problem are summerized briefly. They
serve as the basis for recommendations on an improved
smolder ignition test method which is designed to give
ignition temperatures comparable to those in practice.
The proposed test method requires checking against
full-scale mock-up results before it can be considered
for implementation. Smolder propagation, driven by
buoyant convection, through a thick (18 cm) layer of
cellulosic insulation has been extensively examined. A
heavy (25% add-on) loading of boric acid cuts the
propagation rate in half (from approx. 0.3 to 0.15
cm/min) but does not come close to stopping this
process. Analysis of experimental profiles for
temperature, oxygen level and remaining organic fraction
strongly indicate that the smolder wave is oxygen-supply
controlled and that it involves both first and second
stages of oxidative heat release from the insulation
material. The balance of involvement of the two stages
varies with depth in the layer. It appears that efforts
to develop improved means of suppressing smolder
propagation must be directed at the entire oxidation
process. However, since boric acid is fairly effective
at slowing the second stage of oxidation, most new
efforts should be aimed at the first stage of oxidation
(which also is responsible for smolder initiation).