Assessing the atmospheric dispersion of accidental pollution

The forecast of the propagation of air pollutants released to air intentionally or during accidents may provide great assistance to disaster management authorities. Apart from local measurements, wind tunnel experiments also play an important role in the validation of fast forecast models used for this purpose.

Accidental pollution means if a building or vehicle storing or transporting hazardous substances gets damaged during an accident or disaster, and the stored or transported substance is released to the environment and spread by the wind. Such an event can be dangerous from various points of view, depending on the properties of the spreading material. If the gas is toxic for humans, the effect is clear, and endeavours must be made to reduce the number of people exposed to the toxic cloud as far as possible. In relation to flammable materials, preparations must be made to prevent explosion, furthermore, even in case of liquids, toxic/explosive vapours may be generated by evaporation, which then spread in the atmosphere.

If such an accident occurs, it is important that the intervening authorities (disaster management authority, fire brigade) are able to act appropriately and take the necessary measures (evacuating towns, closing roads etc.). The vapour cloud and the safety thresholds calculated from it can be determined by computer software, where sufficiently accurate models are required that provide fast results at the same time. According to professional literature, the Gaussian model forming the basis of the most popular pieces of software has numerous limitations, so there is a demand for its further development or the development of new models. Measurement results are always necessary for the validation of models, the accuracy of the model cannot be ascertained without them. These measurement results can be obtained by wind tunnel experiments on proportional samples.

During the wind tunnel experiment, trace gas (e.g. ethane or methane) is used instead of a real pollutant, and its concentration is measured on several points of the model environment of the pollution source with high resolution with respect to time. A map of concentration distribution may be made based on the points and the maximum concentration of the pollutant can be determined. The wind tunnel experiment is more appropriate for the validation of fast forecast accidental models than local measurements, because the boundary conditions of the experiment (wind direction, wind speed, atmospheric layers) can be controlled well, can be kept constant and the experiment can be repeated any number of times, thereby providing representative results.

Involved researchers and departments

Gergely Kristóf PhD | BME Faculty of Mechanical Engineering | Department of Fluid Mechanics
Péter Füle MSc | BME Faculty of Mechanical Engineering | Department of Fluid Mechanics
Márton Balczó PhD | BME Faculty of Mechanical Engineering | Department of Fluid Mechanics

Recent publications of BME on the subject

COST ES1006 (2012): Background and Justification Document  COST Action ES1006 “Evaluation, improvement and guidance for the use of local-scale emergency prediction and response tools for airborne hazards in built environments”, May 2012, ISBN 3-00-018312-X  (Edited by: S. Andronopoulos, P. Armand, K. Baumann-Stanzer, S. Herring, B. Leitl, T. Reisin, S. Trini Castelli, contributing authors: M. Balczo, S. Di Sabatino, J. Franke, M. Gerbec, A. Karpinnen, E. Meijer, J. Moussafir, B. Petterson Reif, G. Tinarelli, I. Trijssenaar-Buhre)

(Márton Balczó represented Hungary in this COST Action)