Assessment of Risk of Accidents on the Bridge during the Operation Period

7.4.1 Subsequences or hazards affecting the water quality of the river in cases of traffic accidents

A dangerous river section refers to the section where if human beings drink the water there might be danger of poison, injury or death. Health monitoring shall be carried out in the monitored section to prevent accidents of poison. Traffic accidents cause toxic substances to dissolve in the river. This is called transient-point source pollution. Use the transient-point source 1-dimension river water quality model to forecast the length of the polluted river section and duration of pollution. The formula is as follows:

Where M is the intensity of the transient-point source and is equal to the quantity of goods dumped in the river. Suppose M=1t (because different vehicles have different loads, so for the purpose of the investigation, assume M=1t); in , Q is the waterflow of the river, A is the area of section water passes, D is the diffusion coefficient in the vertical direction (m²/s), D=0.011u²B² /hu_*, ,x is the distance from the point of forecast to the source of pollution, t is the duration (s) after the source of pollution is put.

With this formula, you can forecast the distribution of toxic and/or hazardous substances in the river after traffic accidents happen on the bridge. On basis of this, you can determine the length and duration of each of the dangerous section, monitored section and index-exceeding section.

Table 7.4-1 Analysis of and Calculation for Pollution of Traffic Accidents

Length of Dangerous River Section(m)	Period of Danger (min)	Monitored Section Length (km)	Period of Monitoring (min)	Index-exceeding Section Length (km)	Period of Index-exceeding (h)
400	47	3	106	42.5	28

It can be seen from Table 7.4-1 that the hazards caused to the water quality of Minjiang River by traffic accidents involving toxic and/or hazardous substances are high. The length of the dangerous section is 400 meters long and its duration is 47 minutes. It is worth noting that each affected section in Table 7.4-1 refers to the accumulated length of the section and the duration is also the accumulated time. It does not mean that the whole section exceeds the index during the period. In the initial period, it is the upstream section that exceeds the index, but the downstream section is not affected yet; however, later, the downstream section exceeds the index and the upstream section might have already been restored to the normal condition. This kind of impact is not frequent, but a potential hazard. The possibility of this kind of impact or hazard shall be assessed by the risk.

7.4.2 Risk calculation

In environtology, the general and strict definition of “Risk” is: R (Risk) is the product of P (the probability of accidents) and C (the environmental or health consequences of the accident), i.e.

Hazard of accident generally refers to personal injury or death. So it is usually expressed by the number of deaths. But sometimes it is expressed by economic indexes or other indexes. According to the characteristics of the water environment, this assessment uses the length of the dangerous river section as the consequences of hazards to calculate the risk. If the number of people along the river banks and the number of people of the unit river length are known, it is very easy to convert this into the general risk that uses the number of injuries and deaths as the indexes.

Probability of pollution accidents is expressed by the frequency of vehicles tippling over on the bridge. On the road, many factors are related to the tippling over of vehicles carrying toxic and hazardous chemicals near the waters. These factors include traffic conditions (personal factors of the driver, load of chemical products, speed, traffic flow, road conditions, etc), the weather conditions of the region where the road is located, the length the road crosses the river, etc. Through analysis, probability of these kinds of traffic accidents can be expressed by the following formula:

P=P₀·C₁·C₂·C₃·C₄·C₅

Whereinto: P₀ is the frequency of traffic accidents within the original road section, times/year;

C₁ is the rate of lowering traffic accidents after the new road is constructed;

C₂ is the ratio of trucks among all the vehicle types;

C₃ is the ratio of chemical product transportation among the whole quantity of cargo transportation;

C₄ the ratio of the river section passed by among the whole section;

C₅ is the ratio of vehicles tippling over among general accidents (15%).

7.4.2.2 Analysis and determination of parameters

(1) P₀ reflects the frequency of traffic accidents caused by traffic conditions, road conditions and transportation condition of this road section, the local weather conditions, local driver’s personal factors, etc.

Because the bridge is a new bridge, now take the data collected from an expressway in the southern part of China. This expressway is 153 kilometers long. The average annual traffic accidents per year from 1985 to July 1991 is 950 times/year.

The formula is as follows:

Whereinto, 1.11 km is the length of this project.

(2) C₁ reflects the lowered frequency of traffic accidents on the road due to improvements in road conditions, traffic conditions and safety management conditions. This parameter can be determined via long-term survey, statistics, comparison and analysis of accidents on expressways and common roads. Data shows that, compared with common roads, the rate of traffic accidents on expressways is 0.25 lower. This project is an urban expressway, so C₁ is 0.25.

(3) C₂ is the ratio of trucks among all vehicle types. It is predicted in the feasibility study report of this project that in 2010 the ratio of trucks is 45% and in 2020 the ratio is 43%.

(4) C₃ represents the ratio of vehicles carrying chemical products among all trucks. For this project, it is 5.13%.

(5) C₄ is the length of the river crossed by the road. For this project, it is 360 meters.

The probability of pollution-causing traffic accidents is shown in Table 7.4-2.

Table 7.4.-2 Probability of pollution-causing traffic accidents on Kuiqi Bridge Unit: %

	2010	2020
P	1.95	1.87

It can be seen from Table 7.4-2 that the probability of pollution-causing traffic accidents on Kuiqi Bridge is very low.

For the risk, please refer to Table 7.4-3.

Table 7.4-3 Risk of pollution-causing traffic accidents on Kuiqi Bridge

	2010	2020
R	7.81	7.46

The risk in Table 7.4-3 is expressed by the length of dangerous river section. From Table 7.4-3 it can be seen that the accident hazard in a century is 7.81m of river section (2010) and 7.46m of river section respectively. The risk of accidents is small.

7.4.3 Accidental discharge management and emergency plan

7.4.3.1 Management of accidental discharge

a. Permit for transport

To transport dangerous goods, approval shall be obtained from the transportation management authorities and the permit for transportation shall also be obtained. The vehicle shall be in good condition and equipped with fire extinguishing equipment and marks of dangerous goods. Three-wheel automobile vehicles, non-automobile vehicles and motorcycles are forbidden to transport dangerous goods.

b. Permit for transport dangerous goods

To transport explosives or chemical products, the carrier must hold the permit issued by the public security authorities for transporting explosives or chemical products.

c. Emergency measures for accidents

The national law on environmental protection states that, when an accident happens, the agency that is responsible or the agency that might be responsible shall take immediate measures, notify the organizations and residents that are affected or might be affected, and report the accident to the local environmental protection authorities and other related authorities for investigations.

Pursuant to the national laws and regulations regarding water and air pollution prevention and mitigation, and Fuzhou municipal regulations regarding pollution prevention and mitigation, after Kuiqi Bridge is constructed in the future, accidents of leakage of dangerous goods in this section shall be co-handled by the municipal environmental protection bureau, public security bureau and transportation management authorities.

7.4.3.2 Emergency measures for management of pollution incidents

Traffic-lead pollution incident shall be prevented. Especially for emergency oil pollution or other kinds of pollution, only emergency measures can be taken. It is important to thoroughly implement the “prevention primary and safety first” policy, which contains the following aspects:

(1) The guiding policy for pollution-causing accidents is “prevention primary” and enhancing of management;

(2) While investigating into the risk of environmental pollution caused by accidents, establish a corresponding emergency plan to minimize the losses;

The precondition for implementing this is to make assessment on the environmental risk of the project. Only after the risk types, probability of accidents and the environmental impact of accidents have been defined can specific measures be taken to prevent accidents from happening, thus eliminating the hidden dangers of accidents or lowering the probability of accidents.

The making of an emergency response plan basically includes the following aspects:

(1) Establish a system for response to emergency accidents

In order to respond quickly to emergency accidents, corresponding organizations shall be established. These organizations include the command and coordination center, information center, monitoring center and post-accident work team.

① Command center

This center shall be headed by the road constructor and includes the environmental protection authorities, drinking water supplying company, water resources bureau, water product bureau, pollution cleaning company, etc. It shall be equipped with complete communications equipment. When allowed by conditions, start up the 110 alert system to improve the efficiency of response. Its responsibilities include establishing the emergency system, coordinating the emergency response multi-lateral relationships and commanding the elimination of pollution-causing accidents.

② Information center

This center shall be organized by the scientific research and study units. Its main responsibilities include giving proposals for pollution-preventing equipment, types of equipment, quantities and the storage place according to the historical data, data on natural resources and results of research, and, on the basis of the types of possible accidents, such as collisions, explosions, etc, quickly and scientifically making the guidelines for dealing with emergency accidents to facilitate the decision-making process of the command and coordination center. At the same time, this center shall follow up on accidents and assess its own work so as to improve the work procedures or adjust the orientation of research.

③ Monitoring center

Currently this function is mainly performed by the environmental protection or environmental monitoring authorities. A laboratory shall be established for this purpose. The laboratory shall be equipped with corresponding instruments for analysis and testing, such as gas chromatograph, etc. Its main duty is to conduct analysis of the pollution of the whole water environment and submit reports.

④ Post-accident work team

This team will consist of professional environmental protection personnel (when necessary, legal advisors can be invited). Its main responsibility is to conduct legal research and carry out negotiations regarding pollution-cleaning costs and claims for damages caused by pollution.

(2) Establish the supervision and reporting system

An emergency response system mainly establishes an operation plan that is operable and suitable. This plan is very helpful for handling of emergency accidents. It mainly includes issuing notices, assessments, decisions, mobilization and post-accident work, etc. The routine monitoring and information receiving is mainly the responsibility of the constructor that, once an accident happens, receives and information and without delay notifies the command center, etc, and starts up the emergency response system.

(3) Training and practices

After the emergency plan for accidents has been made, the emergency team (including the water resources bureau, environmental protection bureau, etc) shall, in compliance with the requirements of the plan, carry out practices periodically under presumed conditions and organize theoretic studies to test the operability, suitability and completeness of the plan. In addition, the emergency team shall organize the compiling of Manual for Response to Emergency Accidents. Each member of the team shall hold one copy for reference.

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