Abstract
In order to study the emergency rescue communication system of chemical production, starting from the special environment after the accident of chemical plant, theoretical analysis is used to construct the safety production experiment area of chemical plant for simulation experiment and calculation. The results show that after the accident, the long-term reliable and safe operation and good working electrical equipment should be chosen as the communication equipment for rescue, and the wireless Mesh communication network should be chosen as the communication transmission technology. The signal attenuation law of Mesh communication network is obtained through simulation experiments. It is concluded that Mesh network communication is a safe and effective wireless communication technology in the process of accident rescue in chemical plants. With the development of science and technology, chips with higher performance and faster processing speed can also reduce network delay, which provides theoretical guidance for the subsequent development of communication equipment more suitable for rescue use.
Introduction
The situation of safe production in China is very serious. In recent years, the economic losses caused by various accidents in China are as high as 250 billion yuan per year, accounting for about 2.5% of GDP. The frequent occurrence of accidents not only affects the normal production of enterprises, but also hinders the economic development to a certain extent [1]. Since 2006, China has strengthened the emergency management of safety production accidents, which has alleviated the further deterioration of safety production in China to a certain extent. However, due to the lack of emergency communication system for safety production accidents at the enterprise level, the situation of safety production in China is still very serious [2]. Therefore, it is necessary to study the emergency communication system for safety production accidents at the industrial enterprise level.
In recent years, the emergency rescue work of many major accidents in chemical plants tells us that a perfect emergency rescue communication network can provide great psychological comfort to the trapped and injured, increase the confidence of the trapped and distressed personnel, and greatly improve the efficiency of emergency rescue [3]. It can be said that a perfect emergency communication network is the lifeline of disaster reduction and relief. Especially in emergency rescue, timely and accurate grasp of disaster occurrence area, disaster characteristics, extent of damage and possible impact of disasters on chemical plants, environmental parameters of accident occurrence point and changes of toxic and harmful gases are prerequisites for scientific decision-making. After a malignant accident, the communication, monitoring and ventilation systems are often seriously damaged [4, 5]. Poor communication makes it impossible for commanders to obtain timely and accurate disaster information in factories, especially the concentration and distribution area of explosive, toxic and harmful gases cannot be accurately grasped, which brings difficulties to safe and efficient rescue work, and also threatens the personal safety of rescue team members [6]. There is no accurate understanding and grasp of the disaster situation of the accident mine, and the situation of the rescue team members killed by blind rescue has also occurred, so the rescue team members must carry rescue media communication equipment when they enter the underground rescue survey.
At the disposal sites of some serious and extraordinarily sudden disasters, especially in the disposal process of some regional disasters, the disaster environment of chemical plants is diffusive and changeable. And some chemical plants have undergone great changes in the space structure after deflagration. Restricted by environmental conditions, rescue work in complex environment is very exhaustive [7]. But in order to protect the lives and safety of the people in distress and rescue workers, rescuers also have to bring water, self-help devices, positive pressure respirators, searchlights, stretchers, picks and other equipment into the affected areas, which has very heavy pressure. Therefore, in the process of rescue and disaster relief, it is particularly important for rescue personnel to lighten the burden and have high reliability, comprehensive information collection and communication equipment. Portable and compact wireless communication equipment can undoubtedly enable the rescue team members to quickly put into rescue, simplify the communication link, and enhance their own security. With rescue communication equipment, the rescue team members entering the disaster area can communicate with the rescue base and rescue command center personnel at all levels in real time. The command center at all levels can also accurately grasp the situation of the disaster area, and provide reliable first-hand information for the correct and rapid formulation of rescue plans.
Method
Selection of communication equipment for rescue
The selection of rescue electrical equipment should be based on the long-term reliable and safe operation and good electrical performance in damp, high temperature, explosive gas, dust and other harsh environments. Electrical equipment in explosive environment will cause explosive gas explosion under certain conditions due to equipment failure spark or high temperature surface, which will lead to malignant accidents. Therefore, the purpose of selecting explosion-proof technology is to reduce the probability of explosion caused by electrical equipment to the limit of explosion-proof standard. There are three conditions for explosion. One is that explosive gases must exist at the same time. The other is that explosive gases are within the explosion limit. The third is that there are enough ignition sources to ignite explosive gases. Once a chemical plant producing explosive chemicals has disasters, the possibility of explosive substances existing in a certain area and in the explosion limit range is very high because the original ventilation facilities are damaged to varying degrees.
There are many types of explosion-proof equipment used in explosive gas environment. According to the principle of electrical explosion-proof technology, there are mainly three types: one is to isolate the source of explosion by medium; the other is to control the source of ignition; the third is to limit explosion and isolate the source of explosion by shell. Intrinsically-safe device is a kind of explosion-proof device to control ignition source. It can achieve explosion-proof purpose by limiting the ignition energy of circuit. As the wireless multimedia equipment for mine emergency rescue generally requires portable or hand-held, and the intrinsically-safe hand-held communication terminal has high security requirements, it is suitable for explosion-proof environment.
Research and selection of wireless communication transmission technology
Like the transmission standard of wireless local area network, wireless Mesh communication network is an advanced network structure using multi-hop routing and peer-to-peer network technology. Wireless mesh network mainly consists of two kinds of network nodes: Mesh router and Mesh terminal. The network has the characteristics of continuous dynamic expansion, self-management, self-repair, self-balance and mobile broadband. At the same time, it has the transmission rate needed to transmit multimedia information. The transmission rate of 802.11n standard network generally reaches 100 Mb/s, some can reach 450–520 Mb/s, and the point-to-point transmission covers several kilometres. Meanwhile, this multi-hop network can be designed as an automatic adjustment configuration mode, which enables the network to have “learning” and “self-healing”. The disaster emergency communication system based on wireless Mesh technology can have the functions of broadcasting, multicast, meeting, polling, mass emergency notification short message, mass emergency plan and so on, so as to realize timely and effective communication after disasters.
It is necessary and practical to use emergency rescue wireless multimedia communication system after chemical plant accidents. In the process of post-disaster accident rescue, the rescuers bring portable wireless Mesh multimedia acquisition device, wireless Mesh relay remote transmission device and Mesh gateway base station device into the accident area, connect the Mesh gateway base station to the Ethernet ring network, and arrange wireless Mesh relay remote transmission equipment within a certain transmission distance and a specified range in the process of reconnaissance from rescuers to the disaster area, to form a wireless Mesh relay self-organizing chain network system.
Results and discussion
Characteristic analysis of wireless Mesh subject network for accident area rescue
Compared with the existing ground-based wireless Mesh main body network, the accident area rescue wireless Mesh main body network has the following characteristics.
Point-to-point network structure. Mesh nodes in the Mesh network are adjacent to multiple nodes, so the nodes often present a point-to-multipoint network structure, as shown in Fig. 1A and B. In the accident area rescue wireless Mesh network, it can be seen from Fig. 1A and B that the Mesh node only connects with the left and right sides of the node by setting up, which is called the point-to-point (P2P: Point to Point) network structure, as shown in Fig. 1C.
Different Mesh networking modes (A and B: Point-to-multipoint networking mode for mesh wireless Mesh networks; C: Point-to-point networking mode for chain wireless Mesh).
Power limitation of wireless Mesh relay transmission equipment. Most of the wireless mobile communication instruments are designed to be portable. They must be designed to be intrinsically safe. One part of the equipment is integrated design of power supply devices. The other part is separated design of power supply and equipment. When power supply is needed, power supply is connected by lines or sockets. It is found that the energy of electromagnetic wave is also dangerous to explosive gases. Therefore, unlike the ordinary wireless Mesh network, the power supply of the wireless Mesh relay transmission equipment for rescue in accident area is limited to a certain extent, and the power obtained by the wireless Mesh relay remote transmission equipment from the equipment power supply is also limited, thus limiting the transmission power to a certain extent, and the communication transmission distance is far less than the conventional transmission distance.
Communication information multi-hop transmission. In the actual rescue process, the environment encountered by the rescue team is usually complex. Only the rescue equipment with comprehensive adaptability can be well applied to the rescue process. In conventional wireless Mesh networks, because of the open space and multi-hop transmission, there are usually only a few hops, but in the accident area rescue wireless Mesh network, because the disaster area is a certain distance from the rescue base, and many obstacle areas are caused by the collapse of the factory, there are more non-line-of-sight areas. Moreover, because of the flammable and explosive gas and dust in the accident area, its emission energy must be limited. Therefore, the transmission distance is also limited. On the other hand, the information transmission mode of rescue wireless Mesh network is linear multi-hop, so it is necessary to increase the number of nodes and make multi-hop transmission.
A large number of studies show that the transmission bandwidth of linear multi-hop backbone links will decrease sharply with the increase of the number of hops in wireless links. A large number of simulation experiments on wireless Mesh network routers are carried out in the simulation experiment area of chemical safety production. The experimental steps are as follows.
Two structural diagrams of wireless relay transmission.
The test computer 1 is connected to the relay device 1 with the network wire, and the test computer 2 is connected to the relay device 2 with the network wire. All the above devices are placed in the simulation experiment area, and the specific structure is shown in Fig. 2. Transfer 392 MB test files from test computer 1 to test computer 2. Then through the special test software test, the test results are: 425 M files, taking 371 seconds, 425
Three wireless Mesh remote relay (Mesh node) experiments.
The test computer 1 is connected with the network relay device 1, the test computer 2 is connected with the network relay device 3, and the relay device 2 is added in the middle. All the above devices are placed in the simulation experiment area, and the specific structure is shown in Fig. 3. Transfer 392 MB test files from test computer 1 to test computer 2. Then through the special test software test, the test results are: 425 M files, using 763 seconds, 425
Four or more wireless Mesh remote relays (Mesh nodes) have been tested. When the relay is added to the 10th time (9 hops), the system can no longer transmit video information, and the bit error rate is very high.
The experimental analysis shows that the bandwidth decline trend of 10 wireless relay (9 hops) chain topology backbone networks can be summarized as Table 1.
The Relation between bandwidth decline and number of nodes in chain backbone network
Three wireless relay transmission architectures.
Through experiments, it is not only found that its bandwidth decreases rapidly with the increase of nodes (hops), but also its network delay increases rapidly. When the number of wireless relays exceeds 8, the delay is as high as 0.4 seconds, which can no longer meet the needs of real-time transmission. The network delay law is shown in Fig. 4.
The Relation between chain network delay and number of relays.
As can be seen from Fig. 4, for linear multi-hop networks, each intermediate node relays and transmits information and processes data by relay and remote transmission. At the same time, the signal interference between links makes the concurrent data processing of links impossible to proceed at the same time, which eventually leads to a rapid decline in throughput and a rapid increase in delay.
In the application of Mesh network, the network delay is not only related to the number of nodes, but also to the computing power of nodes and the speed of data processing by related hardware devices. Nowadays, with the rapid development of electronic information technology, chips with higher performance and faster integrated processing speed greatly enhance the speed of data integrated processing and reduce network latency.
Starting from the special environment after the accident in the chemical plant, according to the explosion environment in the process of emergency rescue, safe and effective electrical equipment are selected based on the electrical equipment and the principle of electrical explosion-proof in explosive gas environment. According to the signals in the process of establishing a wireless Mesh network for rescue wireless multimedia communication, the attenuation law of the signals in the Mesh network is studied. It provides research basis for further improving the key technology of wireless multimedia in mine emergency rescue. The research results can further improve the technical level of mine emergency rescue communication in China, and provide theoretical guidance for the development of rescue multimedia communication equipment suitable for the use of mine rescue team members.