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ACS Omega
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ACS Omega
2470-1343
American Chemical Society

10.1021/acsomega.4c05050
Article
Quantitative Risk Assessment of an Oil-Gas-Hydrogen-Electricity Integrated Energy Station in China
Zhao Jianbo
https://orcid.org/0000-0003-4215-2507
Wu Mingkun
Lu Hongpeng
Li Guidong
Xu Yuzhi
https://orcid.org/0000-0001-5376-8353
Tian Mengkui *
College of Chemistry and Chemical Engineering, Guizhou University, Guiyang 550025, Guizhou, China
* Email: tianmk78@126.com.
07 09 2024
17 09 2024
9 37 3888738896
29 05 2024
19 08 2024
25 07 2024
© 2024 The Authors. Published by American Chemical Society
2024
The Authors
https://creativecommons.org/licenses/by-nc-nd/4.0/ Permits non-commercial access and re-use, provided that author attribution and integrity are maintained; but does not permit creation of adaptations or other derivative works (https://creativecommons.org/licenses/by-nc-nd/4.0/).

This paper presents a quantitative risk assessment (QRA) study of an oil-gas-hydrogen-electricity integrated energy station in China. A comprehensive assessment of the station was made in terms of consequences and risks, respectively. Consequence analysis shows that the severity of hazardous chemical leakage accidents in the station is in the order of natural gas, hydrogen, gasoline, and diesel fuel, especially in the liquefied natural gas (LNG) and compressed natural gas (CNG) storage tank areas, which may cause major accidents in the event of leakage. The results of the risk assessment showed that the individual and societal risks of the integrated oil-gas-hydrogen-electricity energy station exceeded the risk acceptance criteria. Moreover, the catastrophic rupture of LNG and CNG storage tanks is the main cause of the unacceptable risk. Additional mitigation measures for them, mainly including the installation of emergency manual shut-off valves, the installation of combustible gas detection and alarm devices, and pressure relief protection devices, can effectively reduce the risk to an acceptable level.

National Natural Science Foundation of China 10.13039/501100001809 22162007 Wengfu Group Co. NA WH-220787(YF) Guizhou Institute of Innovation and development of dual-carbon and new energy technologies NA DCRE-2023-05 Science and Technology Program of Guizhou Province 10.13039/501100018555 [2023]379 Science and Technology Program of Guizhou Province 10.13039/501100018555 [2021]480 document-id-old-9ao4c05050
document-id-new-14ao4c05050
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pmc1 Introduction

Mendeleev, who created the Periodic Table of Elements, probably did not think that hydrogen, the number one element in the periodic table, would become popular in today’s world. In today’s world, the increasing demand and consumption of energy have led to a serious fossil energy crisis and environmental pollution.1 In the face of this, countries around the world have turned their sights on the development and use of clean energy. Hydrogen energy stands out in the global energy transition as a secondary energy source that is diverse, green, low-carbon, and widely used. Many developed countries in the world, such as South Korea, the United States, Japan, and some European countries, have taken hydrogen energy as the center of their future energy strategy and have successively planned development routes for it, clarified policy guidance, gradually refined and improved the content of the policy or planning, and formed a relevant hydrogen energy standard system.2 The development and utilization of hydrogen energy is also an important means to help China achieve its “dual-carbon” goal as soon as possible.3 As of June 20, 2024, 56 cities and regions in China have released strategies and plans for hydrogen energy development. Among hydrogen-related economic industries, hydrogen-fueled vehicles are considered to be one of the most promising ways of utilizing hydrogen commercially.4 A hydrogen refueling station, as an important guarantee for hydrogen energy application, is the key infrastructure for the commercialization of hydrogen fuel cell vehicles.5 The number of hydrogen refueling stations built and their popularity determine the commercial process for hydrogen fuel cell vehicles.6 Along with the development and demonstration of technologies related to hydrogen-fueled vehicles, the infrastructure regarding hydrogen storage and refueling is also developing rapidly across the country. By the end of 2023, China’s hydrogen fuel cell vehicle ownership was about 18,000 vehicles, ranking second in the world. The cumulative completion of 358 hydrogen refueling stations, including 245 in operation, was the world’s first.7 It is expected that by 2030, China’s hydrogen fuel cell vehicle ownership will reach one million vehicles and the number of hydrogen refueling stations will reach 1,000.8 It can be seen that hydrogen refueling stations are an indispensable cornerstone to support the development of the hydrogen energy industry chain.9

Although hydrogen energy has many advantages, the hazardous characteristics of hydrogen gas, which are flammable, difficult to store, prone to leakage, and have a wide range of explosive limits, should not be ignored.10 It is potentially dangerous in the whole hydrogen energy chain including upstream hydrogen production, midstream storage and transport, and downstream application. In recent years, there has been a proliferation of safety accidents due to hydrogen energy in countries around the world, causing not only property damage but also injuries and deaths.11 In 2019, three explosions at hydrogen fueling support facilities occurred in South Korea, the United States, and Norway in less than 20 days. In April 2020, a hydrogen fuel plant exploded in North Carolina. The country faces the same risk. In July 2020, at a hydrogen plant in Dongguan, a hydrogen-filled hose dislodged from its fitting, triggering an explosive deflagration; in 2021, a hydrogen storage cylinder exploded in Zhuzhou City, Hunan Province; and in August 2021, a tube trailer in Shenyang, China, caused a burst accident due to a ruptured hose. Therefore, if we want to commercialize hydrogen energy on a large scale and apply it widely in real life, we must pay attention to the dangerous characteristics of hydrogen. In the future, the number of hydrogen refueling stations will accelerate with the rise of hydrogen-fueled vehicles and, at the same time, will inevitably develop toward more densely populated urban areas.12 But whether the construction of hydrogen refueling stations can provide the public with sufficient safety and a level of risk no higher than that of traditional oil and gas stations has become a bottleneck for their further popularization and development. Therefore, the risk evaluation of hydrogen refueling stations has become a hot research topic for domestic and foreign hydrogen energy-related research institutes.

As an indispensable and important infrastructure in the hydrogen energy industry chain, the safety of hydrogen refueling stations has always attracted much attention, and researchers in various countries have carried out a series of QRA studies of different types of hydrogen refueling stations. Most of the current QRA studies have been conducted on conventional hydrogen refueling stations, mainly gaseous ones. Kikukawa et al. used failure mode and effect analysis (FMEA) and hazard and operability (HAZOP) procedures for hazard identification of a 70 MPa hydrogenation station model, identified and summarized a lot of failure scenarios, and estimated the severity of consequences and probability levels of failure scenarios.13 Zhiyong et al. conducted a QRA study of a gaseous hydrogen refueling station (GHRS) in Shanghai, assessing the risk to customers and employees of the station and third-party members of the public outside the station separately, and concluded that compressor leakage was the main risk-contributing scenario.14 Sun and Kim et al. conducted risk assessments of mobile hydrogen refueling stations in Shanghai and South Korea, respectively, and the results showed that the personal and social risks in both cases were within acceptable limits.15,16 The main sources of risks at hydrogen refueling stations were found to be hydrogen dispenser leaks and ruptures of long pipe trailers by Gye et al. during their QRA study of urban hydrogen refueling stations.17 A jet fire was determined to be the primary risk factor by Suzuki et al. after conducting a QRA on a model of a Japanese hydrogen refueling station.18 To improve the reliability of the QRA results, Kwon et al. used two software packages, Hy-KoRAM and Phast/Safeti, to cross-analyze the hydrogen refueling stations.19 They concluded that the station’s personal risk was unacceptable. A QRA study of hydrogen refueling stations operating in urban areas using PHASTv8.7 and HyRAM by Jeon et al. showed that the risk due to jet fires and overpressure in accidents was lower than the ALARP level.20 In addition, some scholars have conducted quantitative risk assessment studies on another type of traditional hydrogen refueling station, namely, liquid hydrogen refueling stations (LHRS). Kikukawa et al. used a risk matrix to assess the level of risk at liquid hydrogen refueling stations and proposed appropriate safety measures.21 In order to compare the high risk of GHRS and LHRS, Yoo et al. conducted a QRA comparison study and assessed that liquid hydrogen refueling stations are of lower risk.22 Yuan et al. conducted a QRA study of the first liquid hydrogen refueling station in China and found that its individual and social risk exceeded the risk acceptance criteria, with dispenser hose ruptures and compressor leaks being the main causes of unacceptable risk.23

Compared with the single-mode hydrogen refueling station, the integrated energy station with a hydrogen refueling function is more and more favored and is the ideal transition solution for the development of hydrogen refueling infrastructure in China. Integrated energy station means a new type of energy station with two or more types of fueling, refueling, hydrogen refueling, charging/exchange, photovoltaic power generation, and other facilities. However, multiple types of hazardous chemicals are stored in integrated energy stations, and in the event of an accident, the hazards posed could be far greater than those of a traditional hydrogen refueling or gas station. Based on the available literature, safety studies and analyses of integrated energy stations are still very limited,24−26 and there are almost no quantitative risk assessment studies on integrated oil-gas-hydrogen-electric energy stations. Therefore, in this paper, a QRA study was conducted on an in-service oil-gas-hydrogen-electricity integrated energy station in China. This is of positive significance for the safety design and layout planning of future integrated energy stations as well as the development of relevant safety standards and emergency response measures for accidents.

2 Description of the Oil-Gas-Hydrogen-Electricity Integrated Energy Station

The main energy fuels stored and sold at this integrated oil-gas-hydrogen-electricity station include hydrogen, gasoline, diesel, and natural gas. Figure 1 shows the geographic location information on the integrated oil-gas-hydrogen-electricity energy station and the surrounding area. There are various civilian buildings to the west, north, and south of the integrated energy station, and there is also a national highway underneath.

Figure 1 Geographic location of the integrated energy station.

The plan layout of the oil-gas-hydrogen-electricity integrated energy station is shown in Figure 2. Among them, the left area mainly consists of a comprehensive office, station house, storage tank area, refueling area, and gas filling area; the right area mainly consists of a station house, hydrogen storage area, hydrogen filling area, and charging area. In addition, Figure 2 highlights the entire hydrogen refueling process of the integrated energy station. First, 20 MPa of compressed hydrogen is transported from the off-site hydrogen production plant to the integrated energy station via a tube trailer. The hydrogen is then pressurized by a compressor to 45 MPa and stored in high-pressure tanks. Immediately after that, hydrogen at a pressure of 35 MPa is obtained through a pressure relief valve and a cooler and finally injected into the vehicle through a hydrogen dispenser. Since the process technology for refueling and gassing is mature and reliable, it is not described in detail in this paper.

Figure 2 Layout of the integrated energy station.

The surrounding environmental conditions (weather, population distribution) were analyzed in order to carry out a precise risk assessment. Since surrounding environmental conditions can affect the results of risk calculations, similar environmental conditions should be reflected as much as possible. We chose the average meteorological data of the local meteorological office in a year to reflect the real weather conditions of the oil-gas-hydrogen-electricity integrated energy station, as shown in Table 1.

Table 1 Weather Conditions at the Oil-Gas-Hydrogen-Electricity Integrated Energy Station

weather	temp (°C)	wind (m/s)	Pasquill stability	
average day	14.9	5	D neutral-little sun and high wind or overcast/windy night	

Field visits were conducted to survey the number of operators and members of the public at the integrated energy station and at nearby advertising, pharmaceutical, and car sales companies, and the summarized approximations are shown in Table 2.

Table 2 Population Data

area	category	population	fraction indoors	
integrated energy station	operator	10	0.1	
public	35	0.5	
highway	public	30	0.1	
advertising company	operator	2	0.5	
public	20	0.9	
pharmaceutical company	operator	40	0.9	
public	10	0.5	
car sales company	operator	5	0.1	
public	20	0.9	

In this paper, the main ignition sources are identified in the context of the environment around the oil-gas-hydrogen-electricity integrated energy station, details of which are given in Table 3.27 Among them, the ignition sources are calculated based on GB/T 3724-2019 (ignition probability within 1 min), and the vehicle speed and traffic density are shown based on the statistical data of the local transportation department.

Table 3 Potential Sources of Ignition

ignition source	type/shape	ignition probability	traffic density (car/h)	average speed (km/h)	
integrated energy station	ignition polygon	0.9	 	 	
main road	transportation polyline	0.2	2000	60	
sub road	transportation polyline	0.2	100	40	

3 Methodology

QRA is a risk evaluation method that uses quantitative probabilistic risk values (e.g., individual risk and societal risk) to characterize the hazards of a system. The methodology not only systematically evaluates the safety of hydrogen energy infrastructures and provides guidance on their risk mitigation measures but also can be directly used in the development of standards related to hydrogen refueling infrastructures (e.g., safety distances). It has become the mainstream method of hydrogen risk evaluation at this stage, and the evaluation process is illustrated in Figure 3.16−19 We used DNV GL’s SAFETI 8.4 software to conduct a QRA study of the oil-gas-hydrogen-electricity integrated energy station.

Figure 3 QRA flowchart.

The first step was to collect relevant data and information about the subject of the assessment through field research. In the second step, possible hazards such as fire or explosion are identified, and typical accident scenarios are defined. The third step, consequence and probability analysis, analyzes the amount of damage, such as overpressure and thermal radiation, generated by the consequences of the accident, while frequency analysis determines the probability of each case. The fourth step, risk assessment, calculates the risk in relation to the consequences of accidents and the frequency with which they occur. Finally, a comparison is made with the risk criteria to judge whether risk mitigation measures are required to keep the risk within the acceptable zone.

3.1 Hazard Identification

The hazardous substances involved in the oil-gas-hydrogen-electricity integrated energy station are mainly hydrogen, natural gas, gasoline, and diesel. Table 4 summarizes the main hazardous characteristics of these hazardous chemicals.28,29 A large amount of high-pressure hydrogen stored in the integrated energy station may lead to serious accidents, such as fire and explosions, if leakage occurs. Natural gas is highly flammable, can form explosive mixtures when mixed with air, and there is a danger of combustion and explosion when exposed to heat and open flames.30,31 Gasoline and diesel are relatively stable in nature, and the main type of accident following a spill is fire.32 Thus, the two main hazards that can result from an accident at an integrated oil-gas-hydrogen-electricity energy station—fire and explosion—are considered.

Table 4 Main Hazardous Chemicals and Their Hazardous Characteristics at This Station

parameter	hydrogen	gasoline	diesel	natural gas (85% CH4)	
energy density (MJ/kg)	143	46.4	45.4	50.07	
explosion limit (%)	4–77	1.3–7.6	0.6–7.5	5–15	
burning velocity (m/s)	2.65–3.25	2–4	 	0.38	
minimum ignition energy (mJ)	0.017	0.2	 	0.31	

3.2 Scenario Definition

The main hazardous chemicals purchased, stored, and sold by the oil-gas-hydrogen-electricity integrated energy station include hydrogen, gasoline, diesel, and natural gas. These hazardous chemicals are all flammable and explosive in nature, and in the event of a leakage, it may lead to major accidents, such as fires and explosions. Therefore, the accident scenarios of equipment leakage and catastrophic rupture shown in Table 5 were considered in the consequence analysis and risk assessment of the integrated energy station. Since both gasoline and diesel fuel at this station are stored in SF double-deck tanks using horizontal buried storage, tank capacity and risk are not considered for the time being.

Table 5 Accident Scenarios Given by Facilities

 	Inventory	 	 	
equipment	pre. (bar)	temp. (°C)	mass/volume	scenario	leakage size (mm)	
1. Tube trailer	200	20	416 kg	small leak	1.27	
large leak	4.02	
cat. rupture	 	
2. H2 storage tank	450	–40	324 kg	small leak	1.43	
large leak	4.52	
cat. rupture	 	
3. H2 dispenser	350	–25	3.5 kg/min	cat. rupture	 	
4. Compressor	450	40	500 kg/day	cat. rupture	 	
5. LNG storage tank	7	–162	60 m3	small leak	25	
large leak	100	
cat. rupture	 	
6. LNG dispenser	16	–182	100 L/min	cat. rupture	 	
7. CNG storage tank	200	0	7.98 m3	small leak	25	
large leak	100	
sat. rupture	 	
8. CNG dispenser	250	10	250 L/min	sat. rupture	 	
9. Gasoline dispenser	3	25	50 L/min	sat. rupture	 	
10. Diesel dispenser	3	25	50 L/min	sat. rupture	 	

3.3 Frequency Analysis of Accident Scenarios

In this study, the reference values for the probability of hydrogen leakage were taken from the accident database prepared by Sandia National Laboratories (SNL) for the risk assessment of hydrogen refueling stations.33 In addition, the leakage size of each component was set to small-scale leakage (1% A cutoff area) and large-scale leakage (10% A cutoff area) in accordance with the actual size of the hydrogenation-related equipment. And the values of natural gas, gasoline, and diesel leakage probability and pore size were taken with reference to the national standard of the People’s Republic of China, GB/T 37243-2019.34Table 6 summarizes the failure frequencies for typical accident scenarios.

Table 6 Failure Frequency for Typical Accident Scenarios

equipment	scenario	leakage size (mm)	leak frequency (/year)	
1. Tube trailer	small Leak	1.27	1.79 × 10–4	
large Leak	4.02	1.60 × 10–4	
cat. rupture	 	7.47 × 10–5	
2. H2 storage tank	small Leak	1.43	1.73 × 10–4	
large Leak	4.52	1.84 × 10–4	
cat. rupture	 	1.11 × 10–4	
3. H2 dispenser	cat. rupture	 	7.47 × 10–5	
4. Compressor	cat. rupture	 	3.04 × 10–5	
5. LNG storage tank	small Leak	25	1.00 × 10–4	
large Leak	100	1.00 × 10–5	
cat. rupture	 	6.00 × 10–6	
6. LNG dispenser	cat. rupture	 	6.00 × 10–6	
7. CNG storage tank	small Leak	25	1.00 × 10–4	
large Leak	100	1.00 × 10–5	
cat. rupture	 	6.00 × 10–6	
8. CNG dispenser	cat. rupture	 	6.00 × 10–6	
9. Gasoline dispenser	cat. rupture	 	6.00 × 10–6	
10. Diesel dispenser	cat. rupture	 	6.00 × 10–6	

The consequences of accidents after hydrogen, natural gas, and oil leaks are different because of the uncertainty of the ignition time. Therefore, when the probability of ignition is considered, a distinction is made between direct and delayed ignition. The hydrogen ignition probability reference is shown in Table 7.35 The probability of immediate ignition of gasoline is taken as 0.065, the probability of immediate ignition of diesel fuel is taken as 0.01, and the probability of immediate ignition of natural gas is shown in Table 8, all of which refer to GB/T 37243-2019.34 However, the probability of delayed ignition is not currently consulted in the relevant national standards for a relatively accurate value, so the default data of the software is used.

Table 7 Hydrogen Ignition Probability

hydrogen leakage rate (kg/s)	P (ignite immediately)	P (delayed ignition)	
<0.125	0.008	0.004	
0.125–6.25	0.053	0.027	
>6.25	0.230	0.120	

Table 8 Probability of the Immediate Ignition of Natural Gas

P (ignite immediately)	continuous release	instantaneous release	
0.02	<10 kg/s	<1000 kg	
0.04	10–100 kg/s	1000–10,000 kg	
0.09	>100 kg/s	>10,000 kg	

3.4 Risk Criteria

This text uses the risk acceptability criteria recommended by the European Hydrogen Integration Program (EIHP2) specifically for hydrogen refueling stations.36 The probability of individual death should not exceed 10–4 per year for employees and customers of the hybrid oil-hydrogen fueling station. For off-station third-party members of the public, the probability of individual death should not exceed 10–6 per year. The acceptable social risk criterion is 10–5 N2– per year, and the unacceptable social risk criterion is 10–3 N2– per year, where N denotes the number of fatalities in the area. Through these two risk demarcation lines, the social risk is divided into three zones, i.e., the unacceptable zone, the ALARP zone, and the acceptable zone.37

4 Results and Discussion

4.1 Thermal Radiation Impact Range

Hydrogen, natural gas, gasoline, and diesel are all flammable substances, and in the event of a leakage, they are likely to cause a fire when they encounter an ignition source. High-intensity thermal radiation energy from fires can cause serious injuries, equipment damage, property loss, etc. Exposure to thermal radiation of 4 kW/m2 will cause first-degree burns to personnel after 20 s; exposure to thermal radiation of 12.5 kW/m2 is sufficient to ignite wood or plastic; exposure to thermal radiation of 37.5 kW/m2 causes 100% damage to equipment within 1 min and 1% lethality within 10 s.38 When a hazardous chemical leak occurs in an integrated energy station, depending on the amount spilled, the moment of ignition, and differences in location, different types of fires may start including fireballs, jet fires, flash fires, and pool fires (early and late). This paper focuses on showing the consequences of accidents with the widest range of effects of thermal radiation from a fire.

The results of the software simulations show that the consequences of accidents with the greatest range of influence from fire heat radiation are fireballs from catastrophic ruptures of hydrogen and CNG equipment and pool fires from catastrophic ruptures of LNG, gasoline, and diesel equipment, respectively. Figure 4 illustrates the worst-case thermal radiation impact distance. From the figure, it can be seen that CNG storage tanks have the furthest distance from thermal radiation injury of all equipment, with the fireball from its catastrophic rupture causing a maximum fatal distance of 86.5 m and a maximum minor injury distance of 262.11 m. In addition, pool fires from catastrophic ruptures of LNG storage tanks resulted in a maximum lethal distance of 81.95 m, and fireballs from catastrophic ruptures of long hydrogen trailers resulted in a maximum lethal distance of 58.67 m. To prevent these types of major fire incidents, crews should focus on the natural gas and hydrogen storage tank areas of integrated energy stations.

Figure 4 Worst-case thermal radiation impact distance.

4.2 Explosive Overpressure Impact Range

The most immediate mode of impact from an explosion is the blast wave, which could lead to fatalities and damage to nearby buildings. When the explosion generates an overpressure of 0.02 bar, it can damage 10% of the windows and roofs of a house; when it generates an overpressure of 0.14 bar, it can slightly damage the walls and roofs of a nearby house; and when it generates an overpressure of 0.2 bar, it is enough to damage the steel structure of a building.39

Since the scale of hazardous chemical spills at the station varies, so does the extent of the damage that results in explosive overpressure. This text focuses on demonstrating the worst-case scenario where a catastrophic rupture of the device occurs, which is illustrated in Figure 5. As can be seen from the diagram, the equipment with the largest overpressure radius range is the LNG storage tank. In the event of an explosion, structural damage and serious injuries would be caused to the steel frame of the building and personnel within 72.17 m, respectively, and minor damage and tympanic membrane rupture would be caused to the walls of the house and personnel within 103.58 m, respectively. In contrast, hydrogen compressors, CNG dispensers, and diesel fuel dispensers did not generate overpressure of more than 0.02 bar after an explosion.

Figure 5 Worst-case explosion overpressure impact distances.

4.3 Individual Risk Assessment Results

Individual risk is the probability of the individual death of a person at a fixed location in the area due to various potential fires, explosions, and toxic gas leaks from hazardous chemical production and storage units, i.e., the individual mortality rate per unit of time (usually one year). The individual risk contours for the oil-gas-hydrogen-electricity integrated energy station are shown in Figure 6. The fact that no risk contours of 10–4 per year were generated in the graph indicates that the individual risk is less than 10–4 per year throughout the region, which is an acceptable risk for station employees and customers. For third-party publics, individual risk cannot exceed 10–6 per year. However, three of the areas in the figure are wrapped by the 10–6 per year risk contour (in red), which is an unacceptable individual risk for third-party members of the public in that area.

Figure 6 Individual risk contours for the integrated energy station.

Therefore, we did a further risk contribution analysis for this part of the region, and the results are shown in Table 9. The primary risk contributions that contribute to the unacceptable risk to third-party public individuals in these areas are from LNG storage tanks and CNG storage tanks.

Table 9 Individual Risk Contributions in Selected Regions

scenario	region 1	region 2	region 3	
LNG storage tank (catastrophic rupture)	2.01 × 10–6 (83.50%)	6.42 × 10–7 (23.63%)	1.99 × 10–6 (28.76%)	
LNG storage tank (large leakage)	3.91 × 10–7 (16.24%)	2.07 × 10–6 (76.04%)	1.07 × 10–6 (15.41%)	
CNG storage tank (large leakage)	6.08 × 10–9 (0.25%)	9.01 × 10–9 (0.33%)	1.21 × 10–7 (1.74%)	
LNG storage tank (small Leak)	 	 	3.75 × 10–6 (54.09%)	
total	2.41 × 10–6	2.72 × 10–6	6.93 × 10–6	

4.4 Societal Risk Assessment Results

Social risk is complementary to individual risk and refers to the determination of individual risk, taking into account the population density of the area surrounding the source of the hazard so that the probability of a mass fatality or injury does not exceed what is acceptable to the public. It is usually expressed as a curve of the relationship between the cumulative frequency and the number of deaths (F–N curve).

The results of the assessment are illustrated in Figure 7. The F–N graph shows that most of the social risk curve of the integrated energy station falls in the ALARP region and some falls in the unacceptable risk region. Therefore, the social risk of this integrated energy station is unacceptable.

Figure 7 F–N curves of the integrated energy station.

The risk contribution and ranking for each accident scenario are listed in Table 10. As can be seen from the data in the table, the three accident scenarios of LNG storage tanks: small leakage, catastrophic rupture, and large leakage, respectively, occupy the top three positions in the ranking of social risk, especially the catastrophic rupture accident scenario that causes an average of as many as 20.40 deaths, but the frequency of this event is very low, only 6 × 10–6. In order to prevent major accidents, safety management must be strengthened on a regular basis in high-risk scenarios.

Table 10 Risk Ranking and Contribution of Accident Scenarios

risk ranking	scenario	frequency (/year)	average fatalities	risk contribution (%)	risk integral (/avg year)	
1	LNG storage tank (small leak)	1.00 × 10–4	1.81	41.12	1.81 × 10–4	
2	LNG storage tank (catastrophic rupture)	6.00 × 10–6	20.40	27.81	1.22 × 10–4	
3	LNG storage tank (large leakage)	1.00 × 10–5	9.36	21.27	9.36 × 10–5	
4	H2 dispenser (catastrophic rupture)	7.47 × 10–5	0.15	2.55	1.12 × 10–5	
5	CNG storage tank (small leak)	1.00 × 10–4	0.10	2.31	1.02 × 10–5	
6	Tube trailer (catastrophic rupture)	7.47 × 10–5	0.11	1.85	8.16 × 10–6	
7	CNG storage tank (large leakage)	1.00 × 10–5	0.44	0.99	4.38 × 10–6	
8	Gasoline dispenser (catastrophic rupture)	6.00 × 10–6	0.50	0.68	2.98 × 10–6	
9	H2 storage tank (catastrophic rupture)	1.11 × 10–4	0.03	0.66	2.89 × 10–6	
10	LNG dispenser (catastrophic rupture)	6.00 × 10–6	0.44	0.60	2.63 × 10–6	
11	CNG dispenser (catastrophic rupture)	6.00 × 10–6	0.06	0.08	3.60 × 10–7	
12	H2 storage tank (large leakage)	1.84 × 10–4	<0.01	0.08	3.56 × 10–7	
13	CNG storage tank (catastrophic rupture)	6 × 10–6	<0.01	<0.01	1.06 × 10–8	

4.5 Risk Mitigation Analysis

The results of the quantitative risk assessment indicate that the individual and societal risks of an integrated energy station are unacceptable; therefore, risk mitigation measures are required to reduce the risks. The mitigation measures in this paper focus on the two devices that contribute the most to the risk: LNG and CNG storage tanks; include installing emergency manual shut-off valves to cut off the gas source in time; installing combustible gas detection and alarm devices as well as overpressure alarms, which can effectively detect natural gas leakage; and installing pressure relief protection devices and emergency release pipes to quickly release natural gas. The probability of equipment failure can be effectively reduced by setting up these safety barrier systems, as shown in Table 11.40

Table 11 Probability of Major Accidents with and without Safety Barrier Systems

 	without safety barrier systems	with safety barrier systems	
LNG and LNG storage tank (small leak)	1.00 × 10–4	1.00 × 10–6	
LNG and LNG storage tank (large leakage)	1.00 × 10–5	1.00 × 10–7	
LNG and LNG storage tank (catastrophic rupture)	6.00 × 10–6	6.00 × 10–8	

The results for personal risk after the implementation of risk mitigation measures are shown in Figure 8, where it can be seen that the entire integrated energy station is wrapped by the risk contour of 10–7 per year (yellow), which indicates that the personal risk in the areas outside of the station is less than 10–7 per year and that the personal risk to the third-party public is acceptable.

Figure 8 Individual risk contours for the integrated energy station (mitigated).

Figure 9 illustrates the F–N curve after the implementation of mitigation measures at the integrated energy station. It can be seen from the graph that the social risk curves no longer fall in the unacceptable area; they all fall at the bottom of the ALARP area, which indicates that the social risk of the station is within the acceptable range.

Figure 9 F–N curves of the integrated energy station (mitigated).

5 Conclusions

In this paper, a quantitative risk assessment study of an active oil-gas-hydrogen-electricity integrated energy station in China is conducted, and risk mitigation measures are proposed and discussed. This has positive implications for the safety design and layout planning of future integrated energy stations as well as the development of relevant safety standards and emergency response to accidents. The main findings of this study are summarized below:1. The severity of accidents caused by the leakage of hazardous chemicals in the station is in the order of natural gas, hydrogen, gasoline, and diesel, especially in the storage tank area of flammable gases, which may cause major accidents in the event of leakage.

2. The most serious fire and explosion accidents are, respectively, fireballs from the catastrophic rupture of CNG storage tanks and explosive overpressure from the catastrophic rupture of LNG storage tanks. The former has a maximum lethal distance of 86.5 m, and the latter is sufficient to damage the steel frame structure of a building within 72.17 m.

3. In the initial situation, the individual and societal risks of the integrated oil-gas-hydrogen-electricity energy station exceeded the risk acceptance criteria, and the LNG and CNG storage tanks were the main contributors to these risks.

4. Risk mitigation measures have been taken for these two components, mainly including the installation of emergency manual shut-off valves, the installation of combustible gas detection and alarm devices and pressure relief protection devices, which can effectively reduce the risk to an acceptable level.

Based on the research in this review, risk scenarios involving domino effects in integrated energy stations can be further considered and analyzed in the future, aiming to provide a theoretical basis for the construction and safety management of integrated energy stations in the future.

The authors declare no competing financial interest.

Acknowledgments

This work was financially supported by the Natural Science Foundation of China (no. 22162007), the Science and Technology Supporting Project of Guizhou Province ([2021]480, [2023]379), the Wengfu (Group) Co., Ltd. Technology Development Project (WH-220787(YF)), and Project from Guizhou Institute of Innovation and development of dual-carbon and new energy technologies (DCRE-2023-05).
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