A methodology for safe distances calculation as consequence of hazardous substances air diffusion

SANDRA MARIELA GODOY; ALEJANDRO SANTIAGO MIGUEL SANTA CRUZ; SCENNA, NICOLAS JOSE

Rio de Janeiro

Congreso; ENPROMER 2005:the 4th Mercosur Congress on Process Systems Engineering and the 2nd Mercosur Congress on Chemical Engineering; 2005

UFRJ

This work presents a methodology to determine the safe distances (Initial Isolation and Protective Action Distances) when a release of harmful substances as poisonous gases, particulate matter or viruses has occurred, for a local emergency plan with the aim of protecting the general public. We consider the random behavior of wind intensity, wind direction, atmospheric stability and day/night and seasonal conditions, which are uncertain and specific of the region under study. This methodology can be used to compute safe distances for emissions coming from static sources or from transportation accidents. Downwind concentrations that overcome a given critical toxicity index must be calculated in order to determine the impact area. To achieve this purpose, a stochastic simulation based on well-known atmospheric diffusion models is carried out. Data stored in a data base provides distance distributions that correspond to the entire set of incidents considered in the analysis. Then safe distances are determined by selecting the 90th percentile value of the respective distribution. The health criteria used for the analysis are the American Industrial Hygiene Association (AIHA) Emergency Response Planning Guideline Level 2 (ERPG-2) and Level 3 (ERPG-3) for computing the Protective Action and Initial Isolation Distances, respectively. Finally, some hazardous events in the area of Rosario city, Argentine, are presented as study cases.