Keywords

1 Introduction

Fire safety assessment, also known as fire risk assessment, refers to determining the size of the fire risk of the assessment object and determining whether the fire risk is acceptable. Fire risk refers to the possibility of fire; fire hazard refers to the possible consequences of fire; and the evaluation process requires analysis and research on the possibility of fire, as well as the social impact after the fire. The consequences should be analyzed as scientifically and objectively as possible, and a comprehensive and sufficient investigation and analysis of adverse effects, especially non-tolerance effects, should be conducted, and a comprehensive evaluation index system should be established [1].

UK fire safety assessment research is mainly applied to how to scientifically deploy urban firefighting forces in order to achieve the purpose of reducing urban fire losses. The United Kingdom divides typical areas of cities into four risk levels, A, B, C, and D, each of which represents an area with certain typical characteristics. Corresponding to different fire risk levels, the fire brigade has different requirements for the first power and arrival time after receiving the alarm. In the 1980s, Japan carried out urban fire risk assessments for all cities, divided cities into tiers, and strengthened administrative management from the perspective of urban disaster prevention. By calculating the burnt area and burnt rate within the city, the burnt rate is used to quantify the city’s fire risk. Different burn loss rates correspond to different city levels. The lower the burn loss rate, the higher the city level and the lower the fire risk; the higher the burn loss rate, the lower the city level and the greater the fire risk, so corresponding administrative management should be adopted. Measures of fire safety assessment could help manager decide to increase or decrease the firefighting investment. The American insurance business firm adopts the urban public fire classification method. Through a unified index system, this method evaluates the community’s fire-extinguishing ability from three aspects: firefighting, firefighting department, and water supply. The urban public fire protection level is divided into ten levels, with level 1 indicating the strongest firefighting ability in the community, and level 10 indicating the worst firefighting ability in the community. This method is widely used by many insurance companies around the world to determine basic insurance rates in various communities. Because the method is relatively stable and easy to operate, it can promote the local government to improve the level of firefighting power [2].

In the process of petrochemical production, physical and chemical explosion often occur simultaneously: explosion produces combustion, combustion produces explosion, or they alternate with each other. Explosions can rupture pipelines, equipment, and devices, cause material to flow, destroy structures, and kill people. When large-scale equipment and pipelines in petrochemical enterprises are damaged, the flow of chemical raw materials will rush out rapidly, likely to cause large-area flowing fire. DNV process hazard analysis software tool (PHAST) is a software developed by DNV Technical Company in Norway for hazard analysis and safety calculation in the field of petroleum, petrochemical, or natural gas. There are different modes calculation for each period of explosion development: leakage, diffusion, combustion, and explosion of toxic gas diffusion. The compilation group of Chinese National Code GB50074 《Specification for Design of Oil Depots》 applied PHAST software to calculate the safe distance of oil tank fire [3].

2 Confined Space Blast Mode

The confined space explosion models include the ME energy source explosion and the BAKER-STREHLOW-TANG (BST) explosion. The ME explosion method was invented [1], which assumes in the early explosion, overpressure and blasting occur only in confined spaces, the DNV PHAST software uses seven confined space sources (depending on the value of the multi-energy options set for the scene) to simulate that the same confined space contains residual cloud mass that is not part of the confined space. BST explosion is based on spherical free space explosion in the air and does not include the effect of explosion on the ground or adjacent ground, which will increase the intensity of explosion. The differences between ME and BST are as given in Table 1; geometric models could be shown in Fig. 1.

Table 1 ME and BST mode explosion
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Fig. 1
A two-part schematic representation represents the multi-energy model at the top and the B S T model at the bottom. In the multi-energy model, the vapor cloud is hemisphere-shaped, and in the B S T model, it is sphere-shaped. The bottom has some information for the B S T model.

Diagram of ME, BST explosion mode [1]

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3 Personnel Injury Standards Approved

3.1 Personnel Injury Overpressure Criteria

The main destructive effect of explosion is produced by shock wave, which is formed in both chemical and physical explosion. The damage of shock wave can be measured by three characteristic parameters: peak overpressure, duration, and impulse. According to the overpressure criterion, as long as the shock wave overpressure reaches a certain value, it will cause certain damage to the target. The higher the intensity, the greater the overpressure on the wave front. The shock wave produced by the explosion is a vertical shock wave, which is centered on the explosion point and propagates outward from the sphere or hemisphere. With the increase of the radius, the surface area of the wave front increases and the overpressure decreases. According to DOD 5154 Ammunition and Explosives Safety Standard, the Australian oil production and Exploration Association Standard, and the The Green Book, GJB5212-2004 National Military Standard Test Procedure for cloud explosive ordnance, and animal test data from the United States, the former Soviet Union and Japan, form Table 2.

Table 2 Guidelines for simulating human injury overpressure
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3.2 Damage Zone

According to Table 1, assuming that the propane–air mixture with a chemical calculation ratio explodes at low altitudes, the damage and destruction regions of the shock wave are estimated as follows [6]:

  1. (1)

    Dead zone radius: The radius R1 refers to the area where a person dies from a 50% head-to-head impact under a shock wave R1 = 1.98 \(m_p^{0.447}\).

\(m_p\)—The propane equivalent of the flammable gas in a vapor cloud.

  1. (2)

    Serious injury zone radius: The radius R2 refers to the area radius of 50% eardrum rupture under the action of shock wave, and the corresponding value of shock wave overpressure is 44 kPa. R2 = 9.187 \(m_p^{1/3}\).

  2. (3)

    Minor injury zone radius: The radius R3 refers to the area radius of 1% eardrum rupture under the action of shock wave, the corresponding value of shock wave overpressure is 17 kPa. R3 = 17.877 \(m_p^{1/3}\)

4 Methodology

The research flowchart in Fig. 2 will describe how the research was conducted including onsite investigation, data collection, risk recognition, and calculation.

Fig. 2
A flow diagram of the research workflow. It starts with data collection from onsite, followed by risk recognition, risk assessment, quantitative risk assessment, and finally ends at conclusion. Quantitative risk assessment also leads to mitigation, which moves to data collection.

Flow of research work

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  1. 1.

    Investigate key industries and fields of fire safety in Yangpu Economic Development Zone;

  2. 2.

    On the basis of fully obtaining basic data, fire safety engineering methods, fire dynamics analysis software, and other tools are used to mainly conduct fire, explosion, toxic chemical leakage, and other accidents that may occur in the Yangpu Economic Development Zone. Quantitative analysis and simulation calculation;

  3. 3.

    Analyze data and put forward corresponding accident handling suggestions and countermeasures.

5 Modeling Result

5.1 Scene Selection

The Yangpu Economic Development Zone is located in the central area of the Beibu Gulf whose area is 12 km in length from north to south and 7 km in width from east to west with a large number of crude oil, storage tanks for dangerous chemicals, oil and natural gas pipelines, production and processing facilities for dangerous chemicals, and other major hazards [6]. Among the functional areas of the Yangpu Economic Development Zone, the most dangerous fire risky area turns to be petrochemical industry. Huizhi Petrochemical 2000 cubic propane tank and 160,000 m3 CNOOC natural gas were selected based on the most disadvantageous point.

5.2 Huizhi Petrochemical 2000 Cubic Propane Tank

Scene Modeling

The operating pressure of 2000 cubic propane tank of Huizhi Petrochemical is 1.77 MPA, operating temperature is 40 ℃, and continuous leakage time is set to 10 min. In the leakage mode of medium hole (25 mm), large hole (100 mm), and integral rupture, fire and explosion accidents will be caused by ignition source (distance from leakage point is 0 m) as Table 3. ME explosion mode is selected in 70%, 30%, and 10% leakage of the accident. The operating pressure of the 2000 m3 propane tank is 1.77 MPA, the number of molecules is 44 (air 29), and the operating temperature is 40 ℃, at which time it is in the gaseous state. Pool fire (Jet Fire) and vapor cloud explosion (ME hemispherical model) are considered.

Table 3 Consequences of Huizhi petrochemical 2000 cubic propane catastrophic rupture explosion accident
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Huizhi Petrochemical 2000 cubic propane tank exploded in vapor cloud explosion (ME hemisphere model, BST mode) and BLEVE mode; Fig. 3 showed the following characteristics: (1) by comparison of calculated results, the explosion range of ME mode was larger than that of BST mode, vapor cloud was larger than BLEVE mode; (2) the radius of death and serious injury increased with the increase of aperture.

Fig. 3
A line graph depicts the values of seriously injured due to the big hole, medium hole, and small hole, with the highest values of 2181, 328, and 120, respectively.

Explosion casualty curve of Huizhi Petrochemical 2000 cubic propane ME model

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5.3 LNG Storage Tank

Scene Simulation

When the LNG tank bursts and leaks, the liquefied natural gas will vaporize rapidly, forming a cloud of steam with the surrounding air in a confined space. The cloud then absorbs heat from the surrounding environment, gradually heating up and gradually reducing the density to below the air density, when the temperature is close to the ambient temperature, the diffusion process tends to be stable. When the steam cloud meets the ignition source, it will cause the steam cloud explosion accident; if the leakage is large, the LNG that cannot be vaporized will flow to the concave surface and form the liquid pool, which will be ignited and cause the pool fire; if the orifice jet is ignited directly, the jet fire will occur [7].

Consequence analysis of liquefied LNG leakage fire and explosion accident was conducted in LNG storage tank TS-T-0201. The operating temperature of LNG storage tank is − 161.484 °C, the operating pressure is 0.02 MPA, and the continuous leakage time is set to 10 min. In the leakage mode of large hole (100 mm) and integral rupture, fire and explosion accidents will be caused by ignition source (distance from leakage point is 0 m). ME system of default disaster mode was selected as explosion mode in 70%, 30%, and 10% leakage of the accident. The operating temperature of 160,000 m3 LNG storage tank is − 161.484 °C, operating pressure is 0.02 MPA, molecular number is 16 (air 29), and at this time, it is liquid. Consider vapor cloud explosions (BST free-air explosion model and ME hemispherical model). Figure 4 shows the vaporization diagram. Table 4 presents the consequence of TS-T-0201 leakage accident explosion.

Fig. 4
A chart depicts a line graph of pool vaporization rate versus time in seconds which plots a line with the highest value between 0 and 1000 seconds. The left side depicts some details about the material, methane, and the scenario, catastrophic rupture. Some texts are in a foreign language.

Vaporization diagram of CNOOC natural gas LNG tank

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Table 4 Consequence of TS-T-0201 leakage accident explosion
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5.4 Consequences of TS-T-0201 Leakage Fire and Explosion Accident of LNG Storage Tank

After the 160,000 m3 leak explosion of CNOOC natural gas, almost all LNG vaporized to form vapor cloud within 1500S, and the explosion occurred in ME and BST mode, Fig. 5 shows radius of death (m)–leakage concentration, and Fig. 6 shows the consequence of casualty radius–leakage concentration.

Fig. 5
A line graph of the radius of death in meters versus leakage concentrations of 100%, 70%, 30%, and 10% plots 2 decreasing lines. The solid and dashed lines depict the highest values of 226 and 507 meters at 100% leakage concentration, respectively.

Radius of death (m)–leakage concentration

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Fig. 6
A line graph of the radius of severe injury in meters versus leakage concentrations of 100%, 70%, 30%, and 10% plots 2 decreasing lines. The solid and dashed lines depict the highest values of 970 and 1359 meters at 100% leakage concentration, respectively.

Casualty radius–leakage concentration

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The results showed the following characteristics:

  1. (1)

    The less dangerous substances leaked, the area of gas diffusion, the intensity of thermal radiation, the impact of shock wave, and the danger area decrease. From the curves of ME and BST models, the radius of death (the radius of serious injury) decreases with the decrease of the leakage concentration, and tends to linear;

  2. (2)

    At the same leakage concentration, the ME explosion (Series 1) has a larger casualty radius than the BST explosion (Series 2). From the most disadvantageous point of view, the ME explosion mode should be the first choice in PHAST simulation.

6 Conclusion

Taking Huizhi Petrochemical 2000 cubic propane tank and 160,000 m3 CNOOC natural gas as the typical cases, which have the highest fire risk in the Yangpu Economic Development Zone Industrial Zone, the results of PHAST simulation shows the following characteristics: (1) the radius of death and serious injury increases with the increase of leak hole diameter; (2) the radius of death and serious injury decreases with the decrease of leak concentration and tends to be linear; (3) at the same leakage concentration, the lethal radius of ME explosion is larger than that of BST explosion, and the vapor cloud explosion mode is larger than that of BLEVE mode.

Starting from the most disadvantageous point, using PHAST software to simulate petrochemical explosion, the ME explosion mode should be the first choice under the condition of whole rupture and maximum leakage, so as to fully consider the safety capacity of petrochemical engineering.