Abstract
Smouldering fires pose a serious threat in processes that handle organic dusts. They are difficult to detect but can have drastic consequences: besides deteriorating valuable product, they may evolve to open fires and even to dust or gas explosions with potential massive destructive effects. A large number of incidents have occurred in agricultural, food and chemical processing plants, in large storage silo’s, drying equipment and mechanical processing apparatuses, such as mills, cutters or grinders. Smouldering is difficult to detect, because combustion happens at lower temperature, without flames, often in the internal of a porous heap of organic material where the oxygen level is reduced but maintained by diffusion through the porous medium. Detection of smouldering based on carbon monoxide concentration measurement is regularly used in industry. This work presents experimental results of smouldering of several organic products, where the size and temperature of the smouldering nest and the available oxygen is correlated with the emission level of carbon monoxide. This information is essential for the design of reliable smouldering detection systems based on CO gas sensors, especially when process ventilation dilutes combustion gases and low detection levels are required for an early response. Based on new and earlier reported experiments, required detection levels for use in milk spray driers are given.
