Dispersion is used here to describe the way in which effluent from stacks or other building exhaust is transported and diluted by the wind as it passes across the proposed development and immediate neighbours. Extreme air pollution occurs when air pollution reaches excessively high levels for several hours or several days and can cause severe discomfort, diseases and even deaths among the most vulnerable people. Extreme pollution has a high probability of occurrence when there are persistent thermal inversions and weak or stagnant winds due to which effluents cannot be dispersed.
Objectives
The main objectives of the analysis were to:
- Evaluate the temperature rise due to dispersion of hot exhaust gases
- Assess the impact of the exhausts on personnel operations and sensitive receptor locations with respect to NOHSC (Australian Standards) exposure limits for toxic gas and NIOSH exposure limits for temperature
- Assess the impact of the exhausts on crane cabins and with respect to the maximum permissible limit of heat exposure
- Propose design modifications, mitigation measures or operational restrictions to reduce the risk to personnel safety, crane, and helicopter operations
Methodology
Modelling is performed with computer programs that solve the mathematical equations and algorithms which simulate the pollutant dispersion.
Mathematical models can be divided into three categories: geometric, analytical, and computational fluid dynamic (CFD) models.
The most common type of computational fluid dynamics models resolves fluid transport problems by solving a subset of traditional Navier-Stokes equations at finite grid locations. CFD models are used successfully to model internal flow paths within areas, such as vivariums and atriums, as well as in external aerodynamics for the aerospace industry. The aerospace CFD turbulence models, however, are ill suited for modelling the atmospheric turbulence in complex full-scale building environments because of the differing geometric scales.
