The Effect of Forced Draught on the Externally Venting Flame Parameters of Enclosure Fires

Abstract

Wind-driven fires are commonly known in wildland firefighting as they are usually associated with the most catastrophic events resulting in extended fire spreading. They are also important as a research topic in structural fires as wind can significantly impact fire intensity, development and spreading between buildings as e.g. observed in Lærdal fire in Norway (2014) and Cohoe fire in New York (2017). Research results indicate that when wind speed exceeds 16 km/h wind driven fire conditions prevail in the structure that may lead to uncontrolled fire path or may cause “blow torch effect”. This work focuses on further investigating wind impact on fully developed medium-scale compartment fires. A parametric investigation of the effects of wind on the development of heat release rate, temperature and flame dimensions under different forced draught intensity and opening dimensions in cross ventilation conditions. For purposes of this work, testing equipment was developed on open-source platform for measuring and data analyses including scale with continual measurement, temperature data logging, and flame probability estimation. The research determined the critical conditions during the transition of externally venting flames from bidirectional to one-way flow. Experiments verified the use of Archimedes number and critical velocity estimation to predict the change in flow path under different enclosure ventilation conditions. The measurements also validated a new characteristic length and the application of dimensionless mass loss rate to estimate the effect of forced draught to enclosure fire.