1. Introduction
Since the 1960s there has been social conflict and political confusion in Korea due to rapid industrialization and urbanization. In particular, indiscreet urban development has resulted in an unclear distinction between industrial sites and residential areas, causing continuous social conflicts between local residents and businesses [
1]. The Gumi Hydrogen Fluoride Accident in 2012 is an example of this. Within 36 min of the chemical accident evacuations commenced for residents within a 50 m area, and after 4 h and 46 min evacuations were expanded to include all residents within a radius of 1.3 km. Five workers were killed at the scene of the accident, 18 people were killed in the neighborhood, including residents and workers, and a total of 12,243 were hospitalized. In addition, almost all vegetation within 1 km of the accident was affected, causing significant damage to commercial crops and livestock (compensation amounting to South Korean won (KRW) 38 billion) [
2].
This incident demonstrated that chemical accidents not only affect the industrial workers, but also the surrounding communities and natural environment. Because of this accident, the Chemicals Control Act was born in Korea in 2015 and all workplaces that used chemicals were subject to legal restrictions. In the Chemicals Control Act, chemicals that were classified as toxic and dangerous substances were defined as ‘hazardous chemicals’, and detailed guidelines were presented [
3]. However, there is always the risk of this type of accident reoccurring, as many businesses are already in close proximity to residential areas.
In the US (United States) and EU (European Union) the country-based industrial facilities and citizens’ residential complexes are clearly separated, and regulated through land use plans and laws such as the Seveso directive [
4]. These countries aim to prevent chemical accidents through safety management and by ensuring sufficient distance from residential areas during the initial risk assessment when planning industrial building sites [
5].
The Chemicals Control Act outlines how to assess the risk of any chemical facility by determining the risk of all chemicals in the workplace [
6], and the scope of the worst damage is disclosed to local residents and workers of other companies [
7]. The worst damage scenario is conservative yet is considered excessive legal regulation in Korea. However, the safety of the people is the most important value. The purpose of these Chemical Control Act may also apply to other countries. Residents who are within the scope of the worst damage scenario are informed about evacuation sites, first aid measures, and best evacuation practices (e.g., relocate to the center of a building, or evacuate to a higher ground) in the event of an accident [
8].
In Korea, most of the modeling programs for evaluating the extent of damage use the KORA (Korea Off-site Risk Assessment Supporting Tool), which is provided by government agencies [
9]. However, there are many kinds of modeling programs, and even when modeling with the same conditions, the damage radius results are different with different models [
10].
As the Chemicals Control Act suggests only providing chemical accident information to residents in the worst potential damage area, if the damage radius distance differs from one modeling program to another, it may result in some people not receiving necessary information, which leaves them defenseless for when a chemical accident actually occurs [
11].
In this study, we compare the results of three modeling programs by adding Areal Location of Hazardous Atmospheres (ALOHA) and Process Hazard Analysis Software Tool (PHAST) in addition to KORA, a modeling program used in Korea. In this way, we use various modeling programs to select the alternative risk assessment.
4. Discussion
Sulfuric acid was not modeled in the ALOHA program because while it is dangerous to inhale, it is not likely to spread quickly enough in dangerous concentrations to people in large areas under normal conditions. This is due to the low vapor pressure and low volatility of sulfuric acid when dispersed through the air into the atmosphere. It has a very low level of vapor pressure of only 1 millimeter (mm H
2O) at 146 °C, compared to water under the same conditions having a vapor pressure of 44,000 millimeter (mm H
2O) [
25,
26]. The reason why the ALOHA program has the largest damage distance in the summer conditions is that the temperature is high and the atmospheric diffusion of the chemical is expected to be faster.
The ALOHA program has shown great toxic effects in nitric acid and ammonia. In 1996 the ALOHA program versioning was modified to account for the surface tension among the physical properties related to ammonia. In 2009, ALOHA was updated for the reactivity and carcinogenicity of nitric acid. There were also updates made using results from field tests on the marine transport tank conducted by the US Navy in relation to hydrochloric acid and ammonia [
27]. Due to the history of modeling program-specific updates, different results for different “chemicals requiring preparation for accidents” were expected. This update history would have caused the nitric acid and ammonia damage distance to be large in ALOHA. The technical limitations of the ALOHA program are influenced by area and building-related impacts. If the surrounding area is a highly dense environment, such as with many buildings, actual gas diffusion is prevented. However, there is no method to incorporate this factor into the ALOHA program. Furthermore, ALOHA should not be used when the wind speed is less than 1 m/s. In addition, it is impossible to model the reaction that occurs when a chemical leaks into the air and reacts with the atmosphere [
28]. Comparatively, PHAST is a more realistic physical model, in that topography factors can be selected and the setting of the initial leak rate can be applied [
29]. However, PHAST is also similar to ALOHA with building-related impacts. PHAST does not consider high building density and the environment when modeling. The reason for the largest damage distance in spring from PHAST seems to be a combined factor for wind speed and temperature.
KORA is a recently developed program compared to the other two modeling programs (ALOHA: 1980s, PHAST: 1990s, KORA: 2015). Hydrogen chloride has a large damage distance, which is predicted to be similar for other chemicals (e.g., hydrogen fluoride or hydrogen peroxide) due to the after effect of the 2012 Gumi Hydrogen Fluoride Accident. In fact, hydrogen chloride is a substance with a high vapor pressure (40.5 times the atmospheric pressure), which means that the surface of the leaking hydrogen chloride liquid evaporates and vaporizes well. If the leakage area is wider than the modeled condition, the damage distance may be much larger. According to the development background and update records of the three modeling programs, damage radius distance is considered to be different for each modeling program.
KORA is the recommended modeling program in the Korea Chemicals Control Act. KORA had no change in the damage distance based on the weather (spring, summer, fall, winter) condition. This could be a weakness in the modeling program. However, because the Korean Chemicals Control Act progresses the modeling through the annual average weather information, an important modeling factor in KORA is the chemical’s physicochemical properties and storage conditions rather than weather information.
However, the weather environment is an important factor in a damage prediction model. Modeling with annual averages in the Chemicals Control Act should be modified. Especially in Korea, it is reasonable to model by season because Korea’s four seasons are distinct. By comparing KORA with other modeling programs, it is possible to predict which of the five types of “chemicals requiring preparation for accidents” may be mismanaged in the event of a chemical accident. In this study, there are potential problems in the case of nitric acid, ammonia, and formaldehyde. In the case of nitric acid, the damage distance of ALOHA was 14 times higher than that of KORA. Also, ammonia’s damage distance was more than two times higher in the ALOHA scenario than that in KORA. Formaldehyde had a PHAST value nearly three times higher than that of KORA. This suggests that using KORA alone as a modeling program to prevent and respond to chemical accidents in Korea is problematic.
In the case of hydrogen chloride, the extent of the KORA damage predictions results in issuing chemical accident summaries to 2,555,183 people in the surrounding area. This means that not only information summaries are transmitted, but also that various social network infrastructures are required from the local governments (e.g., city hall or county offices), fire departments, police stations, and hospitals to support injured people. Conversely, when modeling with ALOHA or PHAST, support for 10,032 and 159,920 people is relatively low. The difference in the number of people is likely to lead to a larger distribution gap for industrial factories in areas with higher population density. Also, by showing different results for different modeling programs, it demonstrates that the modeling program cannot know exactly how many people will actually be affected by a chemical accident. However, in order to take the highest precautions against chemical accidents, many modeling program predictions are required and must be properly managed.
The modeling results may be different from the diffusion results in real-life. This is a limitation of modeling. If possible, it is also necessary to compare the modeling values through field experiments [
30].
5. Conclusions
In this study, risk assessment was performed using three modeling programs for each of the top five “chemicals requiring preparation for accidents”. It was determined that the modeling program best suited for nitric acid and ammonia accidents was ALOHA, while the KORA program was superior for hydrogen chloride and sulfuric acid accidents, and PHAST for formaldehyde accidents.
The KORA program was seen as an exaggerated result for hydrogen chloride. Materials with high vapor pressure such as hydrogen peroxide and hydrogen fluoride can make exaggerated results in KORA because the Gumi Hydrogen Fluoride accident occurred in Korea. Hydrogen fluoride has a high vapor pressure, therefore, other chemicals having similar physicochemical properties can also cause an accident similar to the Gumi Hydrogen Fluoride accident. Currently, KORA is most commonly used in the Chemicals Control Act assessments, wherein the most dangerous substances are reported as nitric acid, ammonia, formaldehyde, and hydrogen chloride; and these are regarded as exaggerated evaluations. However, most workplaces in the Republic of Korea are located close to residential areas. The Chemical Control Act assumes civilians and workers within the damage radius determined by KORA to be potential victims of chemical accidents. These people are provided with a summary of chemical accident information.
In order to prevent chemical accidents, it is necessary to give as many people as possible warning about the possibility of an accident, and provide evacuation tips in the event of an accident. To do so, a chemical accident scenario derived from a modeling program that represents the worst damage distance should be evaluated and compared against other modeling programs.