Early detection of smoldering in silos: Organic material emissions as precursors

Abstract

The possible use of organic particle emissions as indicators of smoldering fires at low temperatures (early stages, <150 °C) is explored in laboratory experiments. Samples consisting of wood pellets were heated under controlled atmosphere. The sample temperature was slowly ramped, mimicking the spontaneous, slow temperature increase during self-heating in organic materials. As the sample temperature reached 90–100 °C, a two-orders-of-magnitude increase in the number concentration of sub-micrometer particulate matter was measured under both air and nitrogen atmosphere. A detailed analysis of their chemical composition indicated that the particles formed through evaporation of low-volatile organic compounds followed by condensation downstream of the heated volume. The increase in aerosol concentration precedes any significant increase in measured CO and CO2 concentration in both time and temperature. Our results suggest that the sub-micron particle concentration could be considered as an indication of the stages that lead to smoldering fires.