Currently, the prediction of the space-time evolution of an airborne pollutant released during an accidental leak remains hard to assess. However, this prediction is essential in hazardous activities, such as chemical processes or nuclear plants. Indeed, it is essential to know the concentration of an airborne pollutant concentration that can be inhaled by an operator or detected by a monitoring system for operators protection. The study presents a model that describes space-time evolution of an airborne pollutant dispersion in the near-field of an emission source, around a workplace. The case that is considered is a gas leak, following a containment rupture: in this situation, the pollutant dispersion is mainly controlled by the initial leak velocity (gas leak from a breach on a pressurized enclosure or a duct, failure of the glove box containment, etc.). Thus, the leak flow is similar to the continuous or transient jet flow from a slot or a round opening.
The whole work is based on experiments of gas tracing into a full-scale ventilated room, and on multidimensional simulations using Computational Fluids Dynamics tools. The final model is written as equations that are function of various parameters, such as leak geometry, initial gas velocity and emission duration. Moreover, the influence of room ventilation (deflected leak into cross-flows), the influence of room walls (impinging leaks) and buoyancy effects (for high-concentrated gaseous pollutant) have also been numerically studied in the case of continuous leaks. In addition, the proposed equations are easy to use, as an user-friendly application tool was developed in order to quickly calculate the pollutant concentration evolution in both cases of continuous and transient leaks.