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Laboratory and numerical modeling of the formation of superfog from wildland fires

Author(s): Christian Bartolome, M. Princevac, David R. Weise, Shankar M. Mahalingam, Masoud Ghasemian, Akula Venkatram, Henry Vu, Guillermo Aguilar
Year Published: 2019

Smoke from human-induced fires such as prescribed fires can occasionally cause significant reduction in visibility on highways in the southern United States. Visibility reduction to less than three meters has been termed 'superfog' and environmental conditions that lead to its formation have been proposed previously. Accurate characterization and prediction of precursor conditions for superfog is needed to prevent dangerous low visibility situations when planning prescribed fires. It is hypothesized that extremely hygroscopic cloud condensation nuclei from the smoldering phase of a fire can produce a large number of droplets smaller in size than in naturally occurring fog. This large number of small droplets can produce superfog conditions with relatively low liquid water content. A thermodynamics-based model for fog formation was developed. Laboratory generated superfog measured by a Phase Doppler Particle Analyzer determined that mean droplet radius was 1.5 μm and the size distribution could be modeled with a lognormal distribution. Experiments in an environmentally-conditioned wind tunnel using longleaf pine (Pinus palustris Mill.) needle fuel beds provided visibility, heat flux, temperature, humidity, and particle data for model validation. Numerical modeling was used to approximate the growth of a superfog boundary-layer with liquid water content values of 2 g m−3 or greater. The model successfully predicted previous superfog events.

Citation: Bartolome, Christian; Princevac, Marko; Weise, David R.; Mahalingam, Shankar M.; Ghasemian, Masoud; Venkatram, Akula; Vu, Henry; Aguilar, Guillermo. 2019. Laboratory and numerical modeling of the formation of superfog from wildland fires. Fire Safety Journal 106:94-104. https://doi.org/10.1016/j.firesaf.2019.04.009
Topic(s): Fire Effects, Smoke & Air Quality, Smoke Emissions
Ecosystem(s): None
Document Type: Book or Chapter or Journal Article
NRFSN number: 19897
FRAMES RCS number: 57724
Record updated: Aug 27, 2019