ABSTRACT
Release of hazardous materials in urban areas is a major concern in industrial risk assessment. The presence of high population density in such areas multiplies the magnitude of the consequences. In urban areas, many buildings with complex geometries are involved leading to 3D flow fields that strongly influence gas dispersion. Representing such complex geometries simply but realistically in detailed simulation models can be cumbersome and often limit their utility. In this work, a methodology for the construction of 3D urban models and their importation into CFD models was developed through the access to spatial geodatabases, leading to a relatively fast and simple domain design technique. Moreover, since the magnitude of consequences depends on the absorbed dose which in turn depends on both concentration and exposure time, a simple methodology for dose evaluation was developed and implemented in a CFD code that enables the estimation of regions with a given death probability. The approach was developed and applied to a case study with different atmospheric stratification conditions. The results were then compared with those obtained using integral models. It was found that integral models can both overestimate and underestimate the magnitude of consequences related to hazardous material releases in urban areas.
Subject(s)
Chemical Hazard Release/statistics & numerical data , Gases/toxicity , Models, Theoretical , Hazardous Substances , Urban Health , Urban PopulationABSTRACT
Nowadays, thanks to the increasing CPU power the use of Computational Fluid Dynamics (CFD) is rapidly imposing also in the industrial risk assessment area, replacing integral models when particular situations, such as those involving complex terrains or large obstacles, are involved. Nevertheless, commercial CFD codes usually do not provide specific turbulence model for simulating atmospheric stratification effects, which are accounted of by the integral models through the well-known stability-class approach. In this work, a new approach able to take account of atmospheric features in CFD simulations has been developed and validated by comparison with available experimental data.
Subject(s)
Environmental Monitoring/instrumentation , Environmental Monitoring/methods , Gases , Air Pollutants , Algorithms , Atmosphere , Computer Simulation , Models, Statistical , Particle Size , Software , Volatilization , WindABSTRACT
Systemic hypertension is frequently observed in patients with subarachnoid haemorrhage (SAH). Continuing systemic hypertension might augment the risk of rebleeding and also increase the blood flow and blood volume, resulting in more marked cerebral edema and intracranial hypertension. However, reduction of blood pressure might also decrease cerebral perfusion pressure in patient with an impaired autoregulation and in this way enhance the risk of cerebral ischemia. Anti-hypertensive therapy is not recommended to prevent rebleeding after SAH. The agents of choice for reduction of arterial blood pressure might be mixed alfa and beta adrenergic antagonists and barbiturates.
