A dynamic approach for the impact of a toxic gas dispersion hazard considering human behaviour and dispersion modelling.

The release of toxic gases due to natural/industrial accidents or terrorist attacks in populated areas can have tragic consequences. To prevent and evaluate the effects of these disasters different approaches and modelling tools have been introduced in the literature. These instruments are valuable tools for risk managers doing risk assessment of threatened areas. Despite the significant improvements in hazard assessment in case of toxic gas dispersion, these analyses do not generally include the impact of human behaviour and people movement during emergencies. This work aims at providing an approach which considers both modelling of gas dispersion and evacuation movement in order to improve the accuracy of risk assessment for disasters involving toxic gases. The approach is applied to a hypothetical scenario including a ship releasing Nitrogen dioxide (NO2) on a crowd attending a music festival. The difference between the results obtained with existing static methods (people do not move) and a dynamic approach (people move away from the danger) which considers people movement with different degrees of sophistication (either a simple linear path or more complex behavioural modelling) is discussed.

Wind tunnel study of ammonia transfer from a manure pit fitted with a dairy cattle slatted floor.

In dairy cattle systems, most of the feces and urine go to the pit. At the manure pit level, mass transfer of NH3 ([Formula: see text]) has many factors, but practical difficulties hamper a controlled field evaluation. In this study, we propose a methodology for the determination of an alternative, more practical, pit transfer coefficient of NH3 (PTC), and compare it with [Formula: see text] determined from other scientific studies. The aims of this research study were: (1) to develop a wind tunnel set-up which mimics air flow patterns between the slats and above a clean section of a slatted floor section, featuring an aqueous NH3-emitting solution; and (2) to assess how air velocity, turbulence intensity, NH3 concentration ([NH3]) and PTC are influenced by inlet airflow ventilation rate (VR) forced deflection of the air above the slats into the manure pit through varying the deflection angle (DA) of a deflection panel and varying pit headspace height (HH). Main conclusions were: (1) the calculated PTC values presented a good fit to the power function of the air speed near the slats (u) (p < .001) while the average PTC (0.0039 m s(-1)) was comparable to [Formula: see text] values obtained from other studies, by remaining within the range of average values of 0.0015-0.0043 m s(-1); (2) VR and DA significantly impacted [NH3] profiles and PTC (p < .001) and (3) changing slurry pit from 0.10 to 0.90 m HH did not significantly impact [NH3] or PTC (p = .756 and p = .854, respectively).