Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Smoldering Combustion Hazards of Thermal Insulation Materials. Interim Report. October 1, 1979-April 30, 1981.



Thomas J. Ohlemiller


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).
NIST Interagency/Internal Report (NISTIR) -


boric acid, insulation, ignition, propagation, smoldering combustion


Ohlemiller, T. (1981), Smoldering Combustion Hazards of Thermal Insulation Materials. Interim Report. October 1, 1979-April 30, 1981., NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed June 14, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created August 1, 1981, Updated February 19, 2017