[HDS10-03] Impacts of the risk of chemical release from unregistered plant triggered by a future local earthquake in Osaka
Keywords:Natech(Natural hazard triggering technological disasters), Chemical substance management, Atmospheric dispersion, Earthquake, unregistered plants under PRTR system
Osaka City, the center of Osaka Prefecture, was selected as the research area. Osaka City has an office density of 22.3 cases / km2 and a population of approximately 2.7 million, and can be considered an area with a large release volume of chemicals and exposed population in the event of an accident. As for chemical screening procedure, one of the PRTR chemicals, toluene was selected, which also fulfills Volatile Fire Service Class 4. Given the lack of data on the storage volume of unregistered plants under PRTR for predicting outflow at the time of the accident, the storage volume was estimated using the index of employee number of each geographical mesh (1 km × 1 km). The emission factor (emissions / handling volume) and storage conversion factor (storage volume is equivalent to two weeks of annual handling volume) were used to estimate the amount of storage. In the disaster simulation, a chemical substance was assumed to release from one unregistered plant in the event of the earthquake. Atmospheric chemical concentration was calculated using Atmospheric system exposure analysis software (CAMEO / ALOHA version.5.4.7) (USEPA). Subsequently, the calculated atmospheric concentration was compared to Acute Exposure Guideline Level (AEGL) (NAC/AEGL Committee). AEGL differs for each threshold level, with AEGL-3 set to cause fatal health damage, AEGL-2 to severe health damage, and AEGL-1 to discomfort.
As a result, we found that the area with a large amount of chemical storage, of which the population is also concentrated in the daytime had high risks of health damage in case of the accident. The cumulative exposure amounts of volatilized toluene at 5 m and 10 m from the accident site were 98,007 ppm・min and 25,159 ppm・min, which would cause serious health symptoms, since these values were 7 times and 1.8 times that of AEGL-2, respectively. At 30 m and 50 m points from the site, the values were 1,296 ppm・min and 750 ppm・min, which was 1.9 times and 1.2 times higher than AEGL-1, respectively. Therefore, it is important to stay away from the accident site immediately at least for 5 minutes for minimizing the health damage. This study revealed the risks from a small and unregistered plant and specified the extent of inhalation exposure of chemicals, which would lead the proper evacuation recommendations and alerts under Natech events.