Role of oxygen chemisorption in low-temperature ignition of cellulose

Abstract

Destructive fires involving flaming combustion of cellulosic materials often start with smoldering at lower temperatures. Recent studies show that about 70% of household fires start in this manner. A common scenario is smoldering combustion of upholstery or insulation induced by a lighted cigarette or faulty electrical connection. A similar process occurs during the spontaneous combustion of haystacks and wood piles. In the latter case the process starts with biological oxidation of cellulosic material, and further heat may be generated by oxidation of the breakdown products, eventually leading to pyrolysis and charring. An early eyewitness report by Ranke refers to sudden observation of sparks on exposure of the dark inner part of the haystack to the atmosphere. At the suggestion of Buchner, Ranke attributed this phenomenon to the adsorption of oxygen by pyrophoric carbon char. However, his conclusion has been strongly contested in subsequent publications. Compared to flaming combustion of cellulosic materials that proceeds rapidly at higher temperatures, very little is known about the mechanism and kinetics of smoldering and spontaneous combustion that proceed at lower temperatures. It is believed that this type of information will be helpful for the intervention and control of hazardous fires. In this note we reportmore » some of our recent results that indicate that oxygen chemisorption by char could play an important role in the ignition of cellulosic material at lower temperatures.« less