Optimization of multi-level safety information cognition (SIC): A new approach to reducing the systematic safety risk

Reliability Engineering and System Safety 190 (2019) 106497

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Reliability Engineering and System Safety journal homepage: www.elsevier.com/locate/ress

Optimization of multi-level safety information cognition (SIC): A new approach to reducing the systematic safety risk ⁎

Lei Yua,b, , Wu Chaoa,b, Feng Yanxia,b, Wang Binga,b, a b

T

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School of Resources and Safety Engineering, Central South University, Changsha Hunan 410083, PR China Safety & Security Theory Innovation and Promotion Center, Central South University, Changsha Hunan 410083, PR China

A R T I C LE I N FO

A B S T R A C T

Keywords: Safety information cognition (SIC) Multi-level safety information Transmission efficiency Optimization model Risk management

All systems can be associated with and expressed by information. For a normal system, the correct and smooth information exchange is the necessary condition of a safe system. Based on this, we can deduce that safety information which flows correctly and smoothly in a system is very important for safety. Therefore, the aims of this paper are to reduce the Safety Information Cognition (SIC) asymmetry and the safety risk in a system. Firstly, the process of multi-level SIC was innovatively analyzed from the perspective of the flow structure according to the Bayesian network. Secondly, some strategies and a model for the SIC optimization were creatively proposed based on the graph theory. Finally, the application of the optimization model was illustrated with an example. The optimization effect can be obtained by quantitatively comparing the safety information amount between before and after optimization, and the practical result proves that the optimization model works. In general, the optimization model can optimize the transmission routes of safety information and reduce safety information distortion. Our work can provide a new and effective method to improve the information transmission efficiency of multi-level SIC. It can be applied to safety management to reduce the systematic risk in a certain sense.

1. Introduction 1.1. Research scope and significance

study the SIC in a system in order to reduce the risk of safety information distortion. The significance of this research lies in the following four areas:

With the advent of the information age, safety information is a new hot spot of safety science study. From a safety point of view, information plays a vital role in the communication among persons and systems. From a sociological point of view, the main exchange form between people is the transmission of information. Furthermore, people who understand the systematic safety status are mainly by the safety information through Safety Information Cognition (SIC). Actually, SIC closely connects people with matter and system. It makes information a vital element in the field of safety research after the material, energy and human factors. Therefore, it is very valuable to investigate the mechanism of SIC and to build optimization model of SIC in a system for the purpose of reducing the safety risk. In building, factory, traffic, livelihood, etc., people often meet the relevant scenes of SIC, especially in the safety management process. However, SIC is often accompanied by the distortion of safety information, which makes the Safety Information Receiver (SIR) misunderstand the Safety Information Source (SIS), leading to wrong safety behaviors and even accidents. Therefore, it is valuable and necessary to

(1) Research on SIC is very helpful for the research and development of safety public opinion. On the one hand, the development process of safety public opinion is clarified through analyzing the transmission structure of safety information. On the other hand, the efficiency of the Safety Information Transmission (SIT) is improved. Real safety information is more easily understood by the public, which can help to stabilize social emotions and control the safety public opinion. The optimized model can adjust the structure of multi-level SIC, can improve the efficiency and reliability of SIC, and can reduce the possibility of similar safety rumors. (2) The improvement to the efficiency of SIT is very helpful for emergency management. In the emergency management process, safety information is an important resource which has great safety value. The amount of safety information directly affects the effects of emergency management and the consequences of accidents. The disclosure mechanism should be rapidly established to provide comprehensive and accurate safety information support for mitigating the negative impact of emergencies.

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Corresponding authors at: School of Resources and Safety Engineering, Central South University, Changsha Hunan 410083, PR China. E-mail addresses: [email protected] (Y. Lei), [email protected] (B. Wang).

https://doi.org/10.1016/j.ress.2019.106497 Received 3 December 2018; Received in revised form 7 May 2019; Accepted 12 May 2019 Available online 28 May 2019 0951-8320/ © 2019 Elsevier Ltd. All rights reserved.

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Risk perception is a stage of risk cognition. Risk cognition also includes decision making and execution in addition to risk perception. (7) Cognitive psychology: Cognitive psychology [16] uses the viewpoint of information processing to study the cognitive process of accepting, storing and using information. Cognitive psychology is information processing psychology in the narrow sense. The research foundation of this paper is the combination of safety science and cognitive psychology. The use of "cognition" is conducive to the stage division of the safety information transmission. The roles of cognition are as follows: 8) Cognition is the driving force for the information transmission, and it is also the way of information transmission. In other words, the flow of safety information is the process of safety information cognition. 9) Cognition is a process of interaction between SIRs and SISs. It is the process of analyzing, acquiring, storing and executing of SISs by SIRs.

(3) Research on SIC is conducive to safety education. In the past, safety education was extensive, untargeted and rarely effective. Through the analysis of the transmission structure, we can know who is urgently in need of safety education, and find human factors in accidents. Thus it can improve the pertinence and effect of safety education. (4) Last but not least, research on SIC is conducive to risk management and control. When safety information is overly distorted, the possibility of wrong safety actions is increased. As a result the possibility of an accident has increased and the risk is increased. On the other hand, the safety information asymmetry can be reduced by optimizing the SIC. More scientific and reasonable safety decisionmaking and management can be made based on a more comprehensive understanding of systemic safety status. So the possibility of wrong safety actions is reduced, the risk is reduced after optimizing the SIC. It should be noted that SIC is only one aspect of safety risk, because SIC is mainly studied from the risk probability point of view, yet risk also includes other aspects such as dangerous consequences.

1.3. Related work 1.2. Key concepts In recent years, the theory and application of safety cognition had been developed correspondingly with the increasing emphasis on safety information. The previous application studied on safety cognition mainly focused on the areas of food safety [1,2], medicine [3,4], safety culture [5,6], psychology [7], etc. Research contents of safety cognition should be more universal for further development of safety cognition. If readers are interested in safety cognition and cognitive science, relevant literatures and books on safety cognition and cognitive psychology can be consulted. In addition, some researches mostly focused on risk cognition for driving, operating and related aspects [8–11]. There were also many other areas of literature on risk perception [12–14]. In short, previous application studies laid a solid foundation from risk cognition and risk perception, which provided new ideas for the further development of safety cognition. A preliminary theoretical study had been conducted on SIC. Wang et al. [17] linked safety cognition with safety behavior from the perspective of the event chain. Huang et al. [18] began to use risk perception as a research topic. All the above scholars conducted their studies by taking safety cognition as the breakthrough point. In view of this, most safety researches mostly focused on consumption cognition, medicine safety, risk cognition, etc. Many problems had not been solved in the existing research on safety information: (1) the research had not formed a more widely applicable theory, (2) the multi-level SIC had not been thoroughly studied, (3) and safety information distortion had not obtained a strong solution. In real life, accidents are often caused by the cognition deviation of multi-level safety information. However, there is little research on the flow of multi-level SIC. The research on the transmission structure of safety cognition is almost completely missing, and as a result the laws and strategies of safety have not been well developed. Multi-level SIC is very important for safety work, the analysis of transmission structure can expose many safety defects. Therefore it is high time to study the transmission of multi-level SIC which is an important factor in solving safety information distortion and improve systemic safety.

In order to have a better understanding of SIC, the relevant concepts are sorted out. Specific concepts are defined in the general model of SIC [15]: (1) Safety Information Receiver (SIR): SIR is the cognitive person of the safety information and who is also the main body in a certain system. It can be human, artificial intelligence, etc. SIR mainly plays a part in receiving the safety information. It can also transmit the safety information to the next cognitive person. (2) Safety Information Source (SIS): SIS is the main objective which the cognitive person wants to cognize. SIS generates the information of the safety system in the SIC process, and its main task is to produce safety information. (3) Safety information: Safety information is the safety-related correct information, which is received by the SIR from the SIS. Safety information can characterize and reflect systemic safety status, and it can help safety management and safety decision-making. It is important support and source of information for the system to conduct safety management. Highly valuable safety information generated by SIS is called effective safety information. SIT means the safety information transmission. The efficiency of SIT means the transmission quantity of effective safety information in the unit time. Besides, there are many phenomena of safety signal conversion in the process of SIT, such as the conversion of a heat signal into an acoustic signal, etc. Safety signal conversion is generally regarded as the safety information exchange between different signals. (4) Safety Information Cognition (SIC): SIC refers to a series of activities in which SIRs receive, analyze, store, decide and execute safety information. In the process of safety cognition, safety information is passed from SIS to SIR, and then returned to SIS. It refers to the process by which people receive and process safety information to govern their safety behavior. SIC modes are the forms of communication between SIS and SIR. Safety information chain represents the flow of safety information. It connects multiple SISs and SIRs on the flow path of safety information. SIC is also an important part of safety risk management. Because systemic safety risk management requires safety information as evidence and support. (5) Risk cognition: risk cognition refers to a series of activities such as receiving, analyzing, storing deciding and executing information that represents system risks. Risk cognition is the opposite of SIC from a definitional perspective, but they are all researched for system safety. (6) Risk perception: It refers to a series of activities such as receiving, analyzing, and storing information that represents system risks.

1.4. Research goals and methods From what has been discussed above, the main ideas of this article are as follow: (1) The research objective of this paper is multi-level SIC, the main goal of this article is to improve the transmission efficiency of multi-level SIC and reduce the systematic risk. It is our hope to supplement the missing research of multi-level SIC, to provide a powerful 2

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theoretical guidance for optimizing the distribution of safety information. (2) The research method of this paper is to optimize SIC using graph theory [24,25] from the perspective of the transmission structure. The modes of the safety information transmission process are divided according to Bayesian network. (3) The organizational structure of this article: (1) this paper starts with the network structure of SIT. (2) The optimization strategies are obtained by innovatively rearranging the order of nodes from the perspective of the structure. (3) The optimization effect is obtained by comparing quantitatively the amount of safety information through a concrete example. There is significant improvement in the efficiency of SIT, which is also an important breakthrough. 2. Classification of multi-level SIC modes

Fig. 2. The characteristic of risk in the SIT process.

Multi-level SIC modes are complex and diverse in real world. The chains of multi-level safety information are numerous and interlaced, which is similar to the theory of Six Degrees of Separation [19]. In order to analyze the chain of safety information, it has been divided into four types of SIC modes from SIS to SIR. SIC modes are used to reveal the feature and laws of multi-level SIC. From the perspective of safety information chain, the classification of SIC modes is based on the classification of the Bayesian network model [20,21,26]. SIC modes are divided into four types: series mode, parallel mode, polymerization mode, and hybrid mode. The Bayesian network model is used to calculate the probability, while SIC modes are used to describe the flow of safety information. Their purposes are different, and the analysis methods and laws are also different. The next section describes the SIT laws of the four modes.

level, the more loss of the safety information, the more distortion, and the less safety information is received (a low-level node is a node through which safety information flows later). Assume the total amount of safety information is constant, there are two ways of increasing the safety information of the final receiver. One is to reduce the number of transmission nodes, and the other is to increase the efficiency of the SIT. It is believed that safety information is related to the risk. If a rational person has a complete understanding of safety information in the system, his or her behavior is not likely to be wrong. The system with clear safety information is not prone to accidents, and can promote safety or is relatively safe to some extent [15]. In other words safety information distortion is an integral part of the risk. The higher the transparency of safety information, the lower the risk. The degree of distortion of the safety information is proportional to the risk when the positive effect of safety cognition (such as emerging thinking) is not considered. As showed in Fig. 1, it depicts the SIC law of series mode. Effective safety information decreases as the information distortion aggravates, and the risk increases as a result. The phenomenon of risk accumulation is also called “snowball effect”, which is caused by information distortion in the SIT. The “snowball effect” indicates that the risk has the following characteristics: the risk of the former level is accumulated into the next level in the SIT. On one hand, SIR 2 generates the information distortion, which is inherited by SIR 3. On the other hand, SIR 3 has its own internal and external interference which makes safety information lost. Due to these two reasons, effective information received by SIR 3 is less than SIR 2. The reduction of SIR 3 is more than SIR 2, so the distortion of SIR 2 is accumulated into SIR 3 in the SIT. It enlarges the probability of error and increases the risk. Other SIRs are similar to SIR 3. The snowball effect is the result of the accumulating process of safety information distortion, which creates a potential hazard. At some point of time, the distortion of safety information has increased to a critical point, and the prevention and recovery measures have failed, and an accident appears. In order to reduce the accident, it is necessary to control the risk from the generation stage of safety information distortion. The snowball effect model shows that the ultimate risk is increased in the SIT because safety information distortion of each transmission is accumulated. The safety measures should be implemented at the beginning of the distortion accumulation with the goal of reducing accidents. Based on the snowball effect theory, safety information distortion may occur in the process of safety information transmission among people. For example, the risk is formed due to incorrect transmission of an error message. The inaccuracy of the message becomes more and more serious. Now we discuss the degree of risk accumulation in SIT. Assuming the level I of risk is initially generated at the phase of SIR 2, and the risk level is increased by one level when the safety information is

2.1. Series modes of safety cognition Series mode is the most basic SIC mode. It is similar to the game of “Chinese whispers”: safety information flows from SIS 1 to SIR 2, and then flows from SIR 2 to SIR 3, etc. (see Fig. 1). The law of series mode is similar to the phenomenon of the leaky bucket [22]. The amount of safety information is becoming less and less during the process of SIT. This phenomenon is caused by negative factors in the process of SIT, such as SIR's lack of cognition ability, the interference between SIS and environment. In Figs. 1 and 2, the size of the circle represents the amount of safety information. Bigger circle means the corresponding node has more safety information. Safety information is transmitted through multiple levels from SIS 1 to the final level of SIR. Information distortion is gradually aggravated along the transmission process. In summary, the lower efficiency of SIT

Fig. 1. The snowball effect of SIC. 3

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transmitted once. Hence the risk level of the final receiver is IV after the whole process of SIC. Similarly, when the risk is initially generated at SIR 3, the risk level of the final receiver is Ⅲ; when the risk is initially generated at SIR 4, the risk level of the final receiver is Ⅱ. The higher the level of risk is, the more likely the danger occurs. From the end result of the whole process, one can conclude that the risk level of the final stage is related to the stage of risk generation. Therefore, the earlier the risk is generated, the higher the risk accumulation is in the final stage. In series mode, there are some measures to improve the efficiency of SIT: reducing the transmission link; strengthening the strength of safety information, extending the appearance time of safety information; increasing the occurrence frequency of safety information; enhancing the ability of SIRs to receive and transmit safety information, and so on.

safety information, a cognitive person seeks common ground and puts aside the differences; for the opposite or inconsistent safety information, a cognitive person analyzes and contrasts them with each other, the safety information is further selected by personal judgment. In the polymerization mode, the amount of safety information becomes larger in the process from the upper to the lower level, while the risk becomes smaller in the SIT. In effect, polymerization mode is beneficial to increase the amount of safety information and reduce the risk to some extent. In polymerization mode, there are some measures to improve the efficiency of SIT. For example, improving the ability of SIRs to select and judge safety information. 2.4. Hybrid modes of safety cognition Hybrid mode is a combination of series, parallel and polymerization modes in the SIC. Hybrid mode is made up of two or three safety modes. Hybrid mode and polymerization mode are two different modes: polymerization mode is a many-to-one SIT mode; hybrid mode is a combination of multiple SIT modes, it may include polymerization modes or other modes. In the hybrid mode, the transmission law of safety information still conforms to the above three modes. Therefore, the other three modes of measures can be used for reference to improve the efficiency of hybrid mode. In real life, the application range of the hybrid mode is relatively wide. Safety information flow almost always follows a hybrid mode. The hybrid mode is composed of two or other three modes. The relationship between the other three modes and a hybrid mode is similar to the relationship between the series, parallel and parallel-series in a circuit diagram. Therefore, it is necessary to study all four types of SIC modes.

2.2. Parallel modes of safety cognition Parallel mode of safety cognition refers to the one-to-many transmission process, which means safety information flows through one SIS to multiple SIRs of the same level. In parallel mode, the same level of multiple SIRs has different cognition ability, profound or superficial, for the same SIS they received (the same-level nodes are the low-level nodes that are passed). Therefore, these SIRs have different quantity of safety information, which roughly obeys the law of normal distribution [23]. For example, the examination score of safety training obeys the law of the normal distribution. In the parallel mode, the law of risk between the upper and lower level is similar to the series mode. Its risk is a gradual increase in the SIT. The amount of safety information obeys the normal distribution at the same level, and the distribution of safety information presents a peak shape. The risk is inversely proportional to the amount of safety information, so the distribution of the corresponding risk presents a valley shape at the same level of SIR. Suppose it is 1 to the ratio coefficient between risk and the amount of safety information. The risk curve is exactly the reverse shape of the safety information curve, as shown in Fig. 3. In parallel mode, there are some measures to improve the efficiency of SIT: training the weak SIRs who receive less safety information at the same level, or replacing the weak SIRs with a strong person who can receive more safety information, etc. Figs. 4. and 5.

2.5. A comparative study of four modes Characteristics of four SIC modes are compared according to their definition, structures, and knowledge of graph theory [24,25]. In summary, SIC modes are divided into the series mode, parallel mode, polymerization mode, and hybrid mode. Four modes are based on the classification form of the Bayesian network [26]. Besides, there are some different characteristics among the four modes (see Table 1), including the meaning, the number of SISs and SIRs, the processes of transmission, the laws of SIT, etc. In the actual situation, SIC is often multi-level. Safety information is transmitted from one level to the next level. And then it continues to be transmitted to more SIRs. So the process of multi-level SIC was formed. Multi-level SIC is the transmission process between multiple SISs and multiple SIRs. It is also a complex hybrid of series, parallel, and polymerization structures. A safety information chain is formed by the combination of 4 modes, multiple safety information chains interweave to form the network structure of multi-level SIC. And then, the network structure will be studied in the following.

2.3. Polymerization modes of safety cognition Polymerization mode of safety cognition is opposite to parallel mode. It is a many-to-one transmission process. In other words, multiple SISs transmit safety information to one SIR. The safety information of different SISs can affect each other. Polymerization mode is more complicated, multiple SISs pass safety information to the same cognitive person. In polymerization mode, safety information has a strongly subjective selectivity. For the similar

Fig. 3. Risk laws of SIC in parallel mode. 4

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Fig. 4. Structures and characteristics of SIC modes.

and n are integers and greater than 1. There are some ways of obtaining the transmission coefficient, including experimental measurement, cognitive state evaluation, etc. It is unrealistic to use the measurement method to obtain it at every time because there are some difficulties in quantifying the safety information. But the transmission coefficient can be determined by the rating scale. The rating scale is set up the corresponding transmission coefficient based on cognitive persons, systems and transmission conditions in the actual application. The rating scale can evaluate to obtain the transmission coefficient. 3.2. Transmission relationships of effective safety information Through the above research, transmission relationships of all effective safety information can be determined. Firstly, the relationship between SIS and SIR is defined by the transmission coefficient of every two levels. Secondly, the transmission relationship of safety information can also be clarified in four modes. Finally, the effective safety information relationship of the whole structure can be obtained. This section will analyze the relationship between the effective safety information of four modes.

Fig. 5. The optimization model for multi-level SIC.

3. Transmission coefficient of multi-level SIC

1) Series mode: safety information is transmitted between the SIS and the SIR. In series mode, effective safety information becomes less. It is believed the amount of effective safety information transmitted by the SIS is proportional to the effective safety information received by the SIR. So there are relational expressions below:

3.1. The definition of the transmission coefficient The amount decision mechanism of safety information cognition is related to transmission coefficient. The amount of safety information changes due to the selection and judgment of safety information by SIR. Therefore, there is a proportional coefficient between the information amount of SIS and SIR in the process of SIT. In the transmission of the two levels, the transmission coefficient of SIT is the percentage between receiving and transmissible safety information. It aims to describe the transmission relationship of safety information between the upper and lower levels. Transmission coefficient indicates the cognitive attribute and ability. The greater the transmission coefficient is, the more safety information the next level receives. The transmission coefficient of SIT is related to many factors, such as the receiving capacity of SIR, the attribute of safety information, environmental interference. By defining the transmission coefficient, a calculation method of effective safety information is provided. This paper did not consider the positive effects of SIT, such as emerging thinking. When the safety literacy of SIR is high enough, other effective safety information can still be inferred from the insufficient safety information. This is the emerging thinking of SIT. Combining the analysis of safety information, the following definitions are made: the single SIS node is expressed as v1, its corresponding safety information is expressed as I1; the SIR nodes are described as vi, their corresponding safety information is described as Ii (i = 2, 3,…, n); the transmission coefficient is described as ki (0 < ki < 1). By the way, i

I2 = k2•I1

(1)

Ii = ki•Ii − 1

(2)

2) After the analysis, if the effective safety information of the SIS is I1, I2 = k2•I1, I3 = k3•I2, I4 = k4•I3. Among them, k2, k3, and k4 are the corresponding transmission coefficients of the SIS 2, 3 and 4. In addition, I2, I3, and I4 are the corresponding quantity of safety information received by the SIS 2, 3 and 4. Parallel mode: parallel mode can be considered as the combination of multiple series modes. I1 represents the effective safety information of a single SIS. According to the relational expression of series mode, the expressions of parallel mode can be obtained:

I1 =

I2 I I I = 3 = 4 = ……= n k2 k3 k4 kn

(3)

1) Polymerization mode: there is a subjective choice in the SIT between the SISs and an SIR. The relational expression is defined as follows:

I4 = k 4•(I1 + I2 + I3 + ……+In ) 5

(4)

Reliability Engineering and System Safety 190 (2019) 106497 The effective safety information of n SIRs obeys roughly normal distribution in the same level The safety information from different SISs can reinforce and weaken each other in the process of selecting and judging Its laws of safety information are complex

The efficiency of safety information reduced gradually in the SIT

As known to us all, it is hard to quantify safety information at present. Therefore, this paper bypasses the difficulty of quantifying safety information by subtraction of safety information. The change of safety information is analyzed only from the perspective of theoretical research in formulas 1 to 4. Instead of focusing on the specific quantity of safety information, this paper emphasizes on the increasing amount of safety information after optimization. If the information difference appears to be positive value, the optimization is considered effective. If the amount of safety information is known, the transmission coefficient can be calculated. Through the calculation of effective safety information, it is possible to clarify the effective safety information about each node. The calculation result can clearly show the relationship between the one node and other nodes. The influencing factors of the target node are found. Based on the relationship between safety information, the transmission law of the whole network can be obtained, the transmission law can provide a theoretical basis for optimizing the SIT. In addition, transmission law of safety information is also beneficial for systemic safety and accident prevention.

It depends on the specific situation

4.1. Methods 4.1.1. Basic definitions When safety information flows, the safety information chain generates. The nodes at both ends of the safety information chain are defined as SIS and SIR. SIS is the cognitive objective which transmits safety information, and the SIR is the cognitive person which receives safety information. In the entire safety information chains, the source of all safety information is the central node; the safety information of a node needs to be transmitted to the central node i times, this node is an i level node. There are three relationships between the upper and lower levels of the safety information chain, including series, parallel, and aggregation. Series is a one-to-one transmission of safety information, a parallel is a one-to-many transmission form, and aggregation is a manyto-one transmission. 4.1.2. Boundary conditions Boundary conditions: the application scope of the SIC optimization model is a multi-level SIC process, and the transmission structure of a scene is similar to the flow process of multi-level SIC.

Hybrid mode

Polymerization mode

Parallel mode

Based on the above discussion on the four modes, the SIT efficiency is connected with the three factors, including a cognitive person, safety system and transmission environment. The safety information efficiency can be improved from these three aspects. In addition to these three kinds of methods, we hope to gain a new method to improve the efficiency of safety information when three aspects of conditions remain unchanged. A new strategy which can increase the amount of safety information is obtained by analyzing the transmission process, including the nodes, the network, and the transmission route. This method is called the optimization of SIC, which plays a vital role in improving the efficiency of SIT. The ideal optimization result has several features: the distance is the shortest between the center node and the target node, and the transmission coefficient is larger in this transmission path.

n n+1 n

1

n n+1 1

n

n n+1 n

After an SIR recognized, the safety information is passed one by one The cognitive process is from the one SIS to multiple SIRs Multiple SISs transmit the safety information to one SIR The hybrid mode includes two or three other modes Series mode

1

Number of nodes Number of SISs Meaning SIC modes

Table 1 Comparative analysis of SIC modes.

2) Hybrid mode: the calculation method of effective safety information also accords with the above three modes. By applying the calculation methods of four modes, effective safety information of one node can be predicted in a complex network.

4. Optimization of multi-level SIC model

Number of SIRs

Number of edges

Laws of SIT

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4.1.3. Case selections The scope of application of this paper is applicable to the multi-level safety information transmission of emergency management. 6

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Key nodes should be upgraded

Important nodes should be upgraded Key nodes should be upgraded Important nodes should be upgraded Target nodes should be upgraded

–

Target nodes in the same level should communicate with each other Target nodes should be upgraded

A node with the second large transmission coefficients should become the important nodes at each level Important nodes in the same level should communicate with each other Important nodes should be upgraded

Case selection: (1) Multi-level SIC processes: such as multi-level safety education, safety rumors, reporting the accident to the superior step by step, promulgation and execution of safety laws and policies. (2) The transmission structure of a scene is similar to the flow of multilevel SIC, such as safety management effectiveness. The application scope of this paper is quite extensive. On the one hand, the optimization method of SIC can be used to optimize the organizational structure before the accident, which can reduce the blockage and distortion of safety information. After the accidents, it can also be used for the accident investigation and analysis. On the other hand, the optimization method can be used for other multi-level structures that are similar to SIT. The example of this paper is only used as a representative, and the scope of application is not limited to this situation. Many areas can use the theory of this article, such as controlling of public opinion, emergency management, improving the management effectiveness, the optimization of organization structure, safety education, risk management, and accident analysis. 4.2. The optimization strategy of multi-level SIC The efficiency evaluation of safety information is divided into two aspects: the effectiveness and timeliness. They are used to describe respectively the accuracy and speed of safety information in the process of transmission. From the macroscopic and microscopic perspective, the transmission efficiency is divided into the transmission efficiency of the overall network and the target node. This article only analyzes the SIT from the structural aspects, and it assumes that the transmission time of safety information is the same in every two levels. This paper assumes that the transmission coefficient of the same nodes is unchanged before and after optimization. Related concepts are defined as shown below. 1) Node: the center node is one SIS; the primary node is the nearest SIR to the center node, and it is only one step away from the central node; the secondary node of safety information needs to be transmitted twice to the center node; by analogy, the safety information of n class nodes only needs to be transmitted n times to the center node. 2) Key nodes: the key node has multiple outgoing information chains, which also has many subordinate nodes in the next level. Their safety information accuracy can affect the safety information accuracy of the subsequent nodes in the information chain. 3) Important node: the important node has multiple incoming and outgoing information chains. Degree refers to the number of connection between i node and other nodes [27,28]. If the degree of a node is the largest in the network, that is an important node. It reflects the close degree of connection between this node and other nodes. The degree is the number sum of the incoming and outgoing chains to a node. For the important node, its sum of the two chains numbers is largest in the overall network. 4) Shortest path [29]: the shortest path is the path between two nodes through the least nodes, and it reflects the speed of the SIT. Safety information of the shortest path is firstly received by the SIR with a minimum of time. 5) Sequential transmission between nodes: it means safety information is passed from a high-level to the lower level, which can pass through one or more layers. Safety information is passed from each level to the next level starting from the central node, the i level node passes to the i + 1 level node (the i level node is any level node). It is considered that the i level node is higher than the i + 1 level node in the hierarchy. Because the i level node is more close to the central node. 6) Node upgrading: node upgrading is to make a node closer to the

Target nodes

Entire network

A node with the maximum transmission coefficient should become the key node at each level Key nodes in the same level should communicate with each other Key nodes should be upgraded

Target nodes Key nodes

Optimization strategies of effectiveness Range

Table 2 Optimization strategies of safety information.

Optimization strategies of timeliness Shortening the shortest path Important nodes

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center node. If the hierarchy gap between two nodes is greater than or equal to 2, and the higher level node transmits directly to the lower level node, the lower level node can be upgraded to the next level of the higher level node. The main method of node upgrading is to shorten the shortest path by improving the hierarchy of nodes. 7) Out-of-order transmission between nodes: It means safety information is transmitted from low-level nodes to high-level nodes. It brings safety information interaction between any nodes.

important nodes, key nodes, and shortest paths. There are 3 optimization strategies: node with the maximum transmission coefficient becomes the key node at each level, and the node with the second large transmission coefficients becomes the important nodes at each level; key nodes and important nodes are upgraded; key nodes and important nodes communicate with other nodes in the same level. 5) Optimization of the target node: the optimization of the target node is similar to the optimization of the network, which is an additional optimization of target nodes on the basis of the network. In addition to the above three parameters of network optimization, the state of the target node should also be optimized. There are different 3 optimization strategies: safety decisions are made based on safety information of key nodes and important nodes; the shortest path of the target node is shortened; the nodes of same level exchange safety information with each other. After the completion of an optimization cycle, it can be determined whether the optimization has achieved the goal effect through the comparative method and whether the SIT needs to optimize again or not. The result of the first round optimization can be evaluated by a comparison before and after the optimization. If the ideal optimization effect is not achieved, the second round optimization can be started again.

Based on the above concepts, the optimization strategy is analyzed (see Table 2). There are four parameters to optimize the multi-level safety information, including the key nodes, important nodes, shortest path, and target nodes. The optimization of multi-level safety information is divided into two aspects. Firstly, the network is optimized, and then the target nodes are optimized. For the target node, there are 3 kinds of way to improve the transmission efficiency from the view of SIT structure: 1) Starting from the center node, the shortest path is shortened to achieve the purpose of reducing the transmission time by upgrading the target node or cognizing directly the safety information of the center node; 2) Starting from the adjacent nodes, the transmission coefficient of the key nodes should be larger at the adjacent level. The safety information should be reliable and accurate. So the safety information of the key node and the shortest path is seen as the main basis of safety decision-making; 3) 3) Starting from the peer nodes, peer nodes should communicate with each other. Because the single channel can be misunderstood, multiple channels can verify each other. So the safety information can exchange safety information more accurately with each other at the same level. Its optimization strategy is similar to the optimization strategy of the whole network.

The optimization goal of multi-level SIC is to improve the efficiency of SIT. The way of optimizing SIT is to purposefully adjust the order of nodes and change the flow paths, which is to adjust directly with the way of exchange or upgrade nodes in the whole transmission process. The optimization method can be implemented simply and effectively. The conventional method focuses on the cognitive person, the safety system and the cognitive environment, while the optimization of SIT has changed the conventional method of improving the safety information efficiency. 5. Application of optimization model

4.3. The optimization model of multi-level SIT Referring to the literature [30,31], the proposed method is applied to an emergency management example of the explosion rumor accident in Xiangshui County, Jiangsu Province, China. The specific scene of the explosion rumor accident is as follows: worker Liu found the building of Chenjiagang Industrial Park was smoking in Xiangshui county on the evening of February 10, 2011. And then worker Liu just called to tell Sang, other friends, and relatives that the building of Chenjiagang Industrial Park was smoking and the chlorine gas was leaking, allowing them to escape quickly. He did not carry out an investigation to verify his thinking. At that time, Sang was playing cards. Sang immediately told his two dozen players, and the players told their friends and relatives. As a result of the continuous transmission of electronic communication devices, the rumor became more and more intense. It was heard that there would be an explosion, more than ten thousand people packed up luggage and escaped by a car immediately. In the rush to the county town, massive traffic jams and accidents happened to cause four deaths and many others injured. Subsequently, the relevant government departments came forward to refute the rumor. It was claimed that there did not happen to the explosion and leakage accidents in chemical enterprises of Chenjiagang Industrial Park. In order to reduce the possibility of similar accidents, the accident analysis is based on the theory of multi-level SIC optimization, which is studied from a structural perspective as shown below:

According to the discussion above, the optimization model of multilevel SIC is established by combining with four kinds of SIC modes, the transmission coefficient, the relationship of effective information and optimization strategies. The optimization steps of multilevel SIC are analyzed in detail as follows: 1) Refining the transmission process: some safety information chains form the network structure of multi-level SIC, which is drawn according to the process of specific SIT. The network structure is composed of series, parallel, polymerization and hybrid mode. Then the key nodes and important nodes are found. In the end, nodes and structures are deeply analyzed in the network diagram. 2) Determining the transmission coefficient: there are some ways to determine the transmission coefficient, including experiments and evaluation method. The relationship between every two nodes can be clarified by determining the transmission efficiency. From a structural point of view, there are 3 factors that can affect the effective safety information of the target node, including the effective information of the central node, the transmission coefficient of nodes in the transmission path, and the transmission coefficient of a target node. 3) Clarifying the transmission relation: based on the safety information law of four modes, the quantitative relationship between different nodes is attained by calculating in the network. For the node, the influencing factors of the effective information are specifically obtained. Thus it is extremely high time to improve the efficiency of the safety information. 4) Optimization of the network: the three relevant optimization parameters are analyzed through the network structure, including

1) The network model is abstracted from specific scenes for structural analysis (see Fig. 6): Chenjiagang Industrial Park is the center node, Liu is a primary node, sang is a secondary node, twenty players are 3 level nodes, their relatives and friends are 4 level nodes. The relationship between the central node and the primary node is series. The relationship between primary and secondary nodes is parallel, which is the same as the relationship between secondary and 3 level 8

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Fig. 6. The network model of the explosion rumor accident.

the purpose of optimizing the safety information. 5) Optimization of the target node: the shortest paths of SIT are 1-2-37-13 and 1-2-5-8-13. They have a common feature, the node number of these two paths is the smallest. When the transmission coefficient of all nodes is the same, the distortion degree of safety information is smallest in the shortest path. Shortest paths are the optimization of transmission routes, the SIT speed of shortest paths are fastest in all paths. In addition, the target node is upgraded and communicates with the same level. That is to say, the SIR 13 should go to the scene to confirm the explosion rumor after he heard the news. SIR actively cognizes the central node, rather than waiting for other SIRs to inform. According to the theory of structural importance degree in Fault Tree Analysis Method [32], there are three factors can make the greatest impact on I13: the transmission coefficient of SIR 2, k13 and I1. The accuracy of safety information can be improved from the three aspects.

nodes, 3 level and 4 level nodes. The convergence structure of safety information chains is polymerization, such as v3, v5, and v7. In this accident, the primary nodes believed mistakenly that the leakage of chlorine gas would explode in Chenjiagang Industrial Park. It causes all subsequent nodes to receive the wrong safety information, and then the wrong safety decision and action were made. So the primary node is the source of the accident. 2) The following assumptions are made to determine the transmission coefficient: the effective safety information of SIS 1 and the transmission coefficients of all nodes are known; the target node is v13; the largest transmission coefficient of secondary nodes is v3; the largest transmission coefficient of 3 level nodes is v8; the largest transmission coefficient of 4 level nodes is v11. It is not in accordance with the actual situation to change the key nodes and important nodes of SIR. So this optimization strategy of changing the key nodes and important nodes is not adopted, while other optimization methods are considered. The v2 and v5 are key nodes. The importance of nodes (V) is compared by adding up the number of inflow and outflow chains, then v7 = v5 > v2 > v8 >…. In order to improve the safety information efficiency of the whole network, the priority of safety training should be given to the nodes with a high degree of importance. Card players should be training the safety education because of their high importance in the network. The accuracy of their safety information can affect other SIR in the safety information chain, so it is necessary to conduct safety education for those card players. 3) Clarifying the transmission relationship: the calculation results show that effective safety information of v13 is related to I1, k2, k3, k4, k5, k7, k8, and k13. The influence factor of v13 are sorted according to the magnitude of influence: I1 = k2 = k13 > k5 > k7 > k8 > k4 > k3. 4) Optimization of the whole network: the key nodes and important nodes are upgraded according to the optimization strategies; the upgraded nodes can communicate with each other at the same level. SIR 5 and SIR 7 are upgraded into the primary node. They communicate with SIR 2, which can effectively reduce the cognitive error of the SIR 2. The distance between the SIR and the one SIS is reduced, which is called the node upgrading. So the adjustment of the network structure can usefully avoid accidents, which achieves

In summary, the optimized network structure (see Fig. 7) is compared with the previous structure. There are some conclusions as follows [31]: 1) From the aspect of safety information, effective safety information on SIR 13 added a part of I1, I2, I5, and I7 on the basis of the original amount; similarly, the effective safety information of other nodes also increases. 2) From the perspective of risk, as effective safety information increases, the distortion degree decreases. So the risk decreases, the safety of the whole SIC increases. 3) From the time of transmission, the level of the whole network has become 4 layers to 3 layers, which can reduce the transmission time for all nodes; the target node is only one step away from the central node, which greatly reduces the time of safety information transmission. On the basis of Figs. 6 and 7, assume that the transmission coefficient is constant before and after the optimization. The safety information of nodes can be quantitatively contrasted before and after the optimization: 9

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Fig. 7. Optimized schematic of the explosion rumor accident in Xiangshui County.

Change of keynode: I5′ − I5 = I1•k5 > 0

(5)

6. Discussions and conclusions

Change of important node: I7′ − I7 = I1•k 7 > 0

(6)

6.1. Discussions

′ − I13 Change of important node: I13 = I1•k13•(1 + k 7 + k5•k 7 + k 7•k8 + k5•k 7•k8 + k5•k8) > 0

This paper assumes that the transmission time of safety information is the same in different communication processes. The length of the connection is related to the time consumption of safety information between two nodes. Longer connection means longer transmission time. By calculating the time of paths, an optimized network structure can be further designed to reduce transmission time. The result can also be quantitatively compared. Although the method proposed in this paper can compare the amount of safety information, the numerical value of safety information cannot be accurately measured and quantified in a real sense. The purpose of this paper is to improve the flow efficiency of safety information. So our attention is paid to the changed amount of safety information, and it is not necessary to pay attention to the numerical amount of safety information. For this reason, the quantitative study of safety information is not carried out. And the quantification of safety information and the transmission coefficient need further studying, which is pointed out in the discussion section. It is hoped that more experts and scholars will take an interest in this problem and work it out together. In addition, the research objective of this paper is mainly the safety information amount of multi-level SIC. The content distortion of SIC, the distortion of other information and intelligent cognition are further studied in future work [33,34].

(7)

From a quantitative point of view, there are some findings. The safety information of key nodes, important nodes, and target nodes has significantly increased after optimization, especially the target nodes; accordingly, the safety information amount of other nodes at the whole network is increasing as the increasing of these 3 nodes, which can improve the effectiveness and timeliness of the SIT. It proves the rationality and scientificity of the optimization strategy and the model in the process of multi-level SIC. In addition, the selected case is a traffic accident due to unsmooth flow of safety information, one type of safety information distortion event. In order to reduce the adverse consequences caused by safety information distortion, the safety information distortion event of the case is analyzed and optimized. It is worth noting that the safety information distortion event of the case is also within the scope of research in the field of safety, not just traffic accidents. Because the safety information distortion event is a safety incident with safety information as the main line. This article takes the safety information distortion event as a research object, which meets the requirements for the submission of a safety journal. With another serious safety incident taking place in the same place on March 21, 2019, it is indicated that this case and this paper have the value of safety research. This accident is analyzed on the basis of optimization theory. The order of nodes should be adjusted to make a more accurate and effective process of safety information communication. The optimization method is to upgrade the v13, v2, v5, and v7 into a primary node. In addition, four nodes should cognize the SIS 1 at the same time. If the efficiency needs to be further improved, four nodes can communicate more closely with each other. When one of the four nodes has direct cognition with the central node, this one can verify the accuracy of safety information after receiving the safety information; and then this one communicates with other nodes at the same level. After the node is adjusted, more accurate safety information is passed, the possibility of misjudgment is reduced in the SIC. Based on the above examples, the safety information amount of the multi-level SIT increases. The purpose of reducing safety information distortion is achieved, and systemic risk is reduced.

6.2. Conclusions The research ideas of this paper are as follows: (1) In this paper, the whole idea started from the classification of SIC mode. The cognitive mode of safety information can be divided into four kinds: series, parallel, polymerization, and hybrid structure. Each mode has some different features with the number of SISs, the number of SIRs and the law of SIT. The transmission law of safety information is obtained based on four SIC modes. Safety information of series mode decreases gradually in the process of transmission. Parallel structure presents a characteristic of normal distribution at the peer node. The polymerization structure of safety information needs the subjective choice of SIRs. (2) Then the influencing factors of effective safety information are obtained by defining the transmission coefficient. The transmission 10

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coefficient obtained the relationship of the entire network. The flow of multi-level SIC was studied by analyzing the structure and characteristics. (3) Finally, the optimization strategy was proposed. It is proved that the cognitive efficiency of safety information was improved through an example to make a quantitative comparison before and after optimization. Taking the safety rumor as an example, multi-level safety information distortion is reduced through the adjustment of organizational structure. Systemic risk has become smaller, the effect of optimization is very obvious. So the optimization strategy achieves the purpose of the study on the multi-level SIC. The optimization of SIC can do reduce the systematic risk and improve the systematic safety state. The research fruits of this article enriched the safety management knowledge in information aspects.

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