Fire Patterns on Upholstered Furniture: Smoldering versus Flaming Combustion

In most fire investigations, fire damage patterns provide important clues regarding the origin and cause of the fire. Historically, many fire investigations have relied on intuition to interpret fire patterns, the results of which have often been inconsistent with scientific principles. NFPA 921, Guide for Fire and Explosion Investigations, which advocates the scientific method for forensic investigations, includes a summary of many fire patterns and interprets them based on scientific disciplines such as fire dynamics, heat transfer, and materials science. But NFPA 921 does not address the fire pattern that appears on upholstered furniture when it is first item ignited.In this study, a test program was conducted to determine the nature and extent of fire patterns on upholstered furniture caused by smoldering versus flaming ignition sources. Smoldering fire patterns tended to consist of char zones with a thickness equal to that of the fuel element. Conversely, flaming fire patterns had thin char zones with thicknesses much smaller than the thickness of the fuel element. After a smolder-to-flame transition, the fire patterns created by smoldering were rapidly destroyed by the flames and replaced by flaming fire patterns.In nine tests out of ten, the origin of the fire was coincident with the location of burnthrough (a penetration caused by the consumption of a fuel element) in the upholstered furniture item. However, asymmetric flame spread caused by unusual construction features could lead to burnthroughs in other locations. A burnthrough was observed in all six tests in which a transition from smoldering to flaming fire behavior occurred.Only in earliest stage of the ignition sequence will the physical evidence of the ignition source—smoldering or flaming—be preserved. Thus, to determine the cause of a fire, the investigator may need to rely on a consideration not only of fire pattern observations but also the human and environmental factors which may have contributed to the ignition event. This is an approach often called system safety.