2.1. Offsite Consequence Analysis

The OCA tools used were KORA version 2.0.0.0 [21] from KOR’s NICS, and ALOHA version 5.4.4 [22] from the USEPA. In terms of hazardous chemical substances, the frequency of accidents and the amounts used were ranked in the following order, based on accidents from 2009 to 2015: hydrogen chloride, nitric acid, ammonia, and hydrofluoric acid [23,24]. The concentrations of aqueous solutions were taken into account for the accident cases [25], along with concentration ranges supported by the KORA and ALOHA tools [21,22]. Therefore, the chemicals used were 28% ammonia (NH₃), 35% hydrogen chloride (HCl), 50% hydrofluoric acid (HF), and 69% nitric acid (HNO₃).

The scenarios were based on contents of leakage accident cases provided by the National Institute of Environmental Research [26]. Accident scenarios are defined as those in which 10-mm-diameter holes occur in storage tanks (operating temperature of 25 °C, operating pressure of 1.0 kg/cm²) containing 30 tons of hazardous chemicals in an aqueous solution, with leakage occurring for 10 min. The endpoint concentration for estimating the extent of the impact was applied to emergency response planning guidelines (ERPG)-2 values of the American Industrial Hygiene Association (AIHA) [27]. Table 1 shows input information of the KORA and ALOHA tools for modeling, according to scenarios tested.

Input data provided to the tools.

The common weather variables in the KORA and ALOHA tools are wind speed, air temperature, humidity, and atmospheric stability. Variable conditions for wind speed, air temperature, and humidity were based on Korean weather information provided by the Korean Statistical Information Service (KOSIS) [28]. Air temperature was altered between −5 °C and 35 °C, at a rate of 5 °C. Wind speed was varied from 1 m/s to 16 m/s (maximum daily wind speed), in 1 m/s increments. Humidity was varied from 10% to 90%, at a rate of 10%. Atmospheric stability was altered from unstable (A) to stable (F). Surface roughness was divided into urban and rural [11]. We obtained a total of 640 results using the OCA tools. Table 2 shows a sample of some OCA results.

Offsite consequence analysis (OCA) results for 50% HF and 28% NH₃ by weather variables (N = 640).