Vol. 8, No. 1, pp. 10-13, June 2009

Web Information Systems for Safety and Health Monitoring in Subway Stations

Gi Heung Choi* Department of Mechanical Systems Engineering, Hansung University, Seoul 136-792, Korea (Received March 4, 2009; Accepted June 12, 2009)

Abstract : In this study, a framework for web-based information system in VDN environment for safety and health monitoring in subway stations is suggested. Since physical variables that describing safety and health need to be closely monitored in multiple locations in subway stations, concept of distributed monitoring network using wireless media needs to be implemented. Connecting remote wireless sensor network and device (LonWorks) net- works to the IP network based on the concept of VDN can provide a powerful, integrated and distributed moni- toring performance, making a web-based information system possible.

Key words: Safety, Health, Subway Station, In-door Air Quality (IAQ), Web-based Information System,

1. Introduction 2. VDN-based Web Information System

In crowded subway stations ensuring the safety, health 2.1 Framework for Web Information System and comfort of passengers and occupants is very impor- By connecting local device network into IP network, tant. A key factor that affects the safety and health of multiple sites/locations can be simply integrated into a passengers and occupants is in-door air quality (IAQ)[1, seamless virtual device network (VDN)[5, 6]. The VDN 2, 3]. IAQ can be defined in a more generic building includes one or more remote sites connected with one environment as the physical, chemical and biological or more monitoring/control applications located on the properties that indoor air in the subway stations must Internet. The general architecture of a VDN is shown in have in order not to cause or aggravate illness of pas- Fig. 1. One example is virtual machine (VM) or smart sengers or occupants, and to secure high level of safety, machine (SM), which utilizes the virtual device network health and comfort to them in the performance of the (VDN). In this configuration, monitoring of IAQ, safety designated activities for which the station has been and health management, and predictive maintenance, for intended and designed[4]. example, can be performed both in the subway stations In subway stations intensive and customized and in remote site through internet. information has to be provided to operators and also to One key concept in Fig. 1 is the peer-to-peer commu- passengers. In this study, a framework for web-based nication. Fire accident in 2003 in a subway station in information system in subway stations is considered. the city of Daegu in Korea which killed nearly 200 pas- Specifically, in view of safety, health and comfort man- sengers indicates that such configuration is particularly agement in “Virtual Device Network” (VDN) environ- effective in ensuring the safety of passengers. Commu- ment, a basic framework for integrating wireless sensor nication and transfer of monitoring data (and control network with LonWorks/IP Gateway/Web server is sug- data if necessary) between two adjacent stations, needs gested to perform monitoring of IAQ. to be assured to secure proper safety management and to save lives of passengers in case of fire, or any other disaster. Ventilation and smoke control is a good exam- *Corresponding author: [email protected] ple in case of fire. Web Information Systems for Safety and Health Monitoring in Subway Stations 11

Fig. 2. Concept of LonWorks/IP smart machine using various communication media for monitoring and control of IAQ Fig. 1. VDN based web information system realized in distrib- uted server-client environment using LonWorks/IP Gateway/ Web server. must be transmitted to other devices in the LonWorks network or other client through LonWorks/IP server in the form of NV. The values of NV can then be moni- 2.2 Wireless Sensor Network tored in real time. Considering the fact that physical properties, pollut- ants such as particulate, VOCs and biological agents are 3. Security Issues in the IP Network closely monitored and controlled in multiple locations in the subway station, concept of distributed monitoring LonWorks/IP data transmission is performed by the and control network such as LonWorks network tech- tunneling technique in Fig. 3 which is the core part of nology needs to be implemented. The suggested frame- EIA/CEA-852 standard established by CISCO and Ech- work was designed to deal with various communication elon. Fig. 4 depicts a security check logic described in media shown in Fig. 2. EIA/ LonWorks/IP tunneling standard. A tunneling tech- Wireless media such as Zigbee was particularly sug- nique encodes the communication packet of LonWorks gested for ease of installation. Zigbee network uses including address information device networks as well 2.4 GHz baseband frequency. Simple tests, however, as the network variable binding information into the showed that the communication length between Zigbee data packet of an IP protocol. Data (LonWorks packet) modules in a complex building structure may be short- ened. In that case, 424 MHz wireless communication media may be used to have stronger diffraction perfor- mance. Electromagnetic interference due to power line of the train especially when the train moves along the plat- form also severely degrades the real-time transmission performance of the wireless media. In that case, twisted pair communication media needs to be used. Power line media was considered for the case where twisted pair communication channel can hardly be installed in addi- tion to the existing facilities in the station. Zigbee to Lonworks converter (ZL converter) transforms wireless communication data into network variable (NV) data, Fig. 3. Packet configuration and data format in EIA/CEA 852 then transmitted through LonWorks network. Any data LonWorks/IP tunneling standard. 12 Gi Heung Choi

4. Implementation in the Subway Station

Fig. 5 shows a sample web information page for a metro subway station of Line 5 in Seoul. This web page shows multiple sensor readings at different loca- tions in the station. Preliminary test results in a metro subway station showed that data loss occurred as the distance between two adjacent sensor nodes becomes longer[1]. The number of data received for a Zigbee module located 35 meters away from the sensor node on the same floor in Fig. 5, for example, was around 70% of all data transmitted. It is, however, noticed that as the node moves two to three meters away from the Fig. 4. MD 5 authentication as specified by EIA/CEA 852 stairway to the lower floor data reception was impossi- LonWorks/IP tunneling standard. ble. In case of inter-floors communication, the communi- and the 128 bit secrete word are then encoded using cation distance becomes much shorter than planar case MD 5 algorithm to construct an IP packet. This packet and is estimated to be less than 30 meters. The maxi- is transmitted to the receiving L/IP web server where mum transmission power of Zigbee node used was 1 the decoding process is performed. The receiving Lon- mW which requires the ad-hoc use of such nodes to Works/IP web server first encodes the transmitted data guarantee the usefulness of wireless data communication with its own 128 bits secrete word to check if the in metro station environments. Another possible way to packet is from the authorized web server. Once the guarantee the whole reception of sensor reading is to security check is passed, it transmits the LonWorks data use wired network for inter-stairs communication and to the destination device on the lower device network wireless communication for each floor. according to the NV binding information it received. Fig. 6 shows the web page for monitoring the temper- An L/IP web server on virtual device networks becomes ature, the humidity, the level of CO, CO2 and particu- a connection pass, which can transmit and receive the late at a single sensor node in the subway station. data/information of device networks safely in this method.

Fig. 5. A sample web information page for safety and health monitoring in a metro subway station in Seoul. This web page shows multiple sensor readings at different locations in the station. Web Information Systems for Safety and Health Monitoring in Subway Stations 13

ture in the stations.

Acknowledgement

This research was supported by the Hansung Univer- sity in the year 2009.

References

[1] Gi Heung Choi and Gi Sang Choi, “A Framework for Web-based Monitoring and Control of Indoor Air Quality (IAQ) in Metro Subway Station” Proceedings of International Symposium on Safety Science and Technology, pp. 2514-2518, Beijing, China (2008) [2] Gi Heung Choi and Gi Sang Choi, “Design of Service System Framework for Web-based Monitoring and Control of Indoor Air Quality (IAQ) in Subway Sta- Fig. 6. LonWorks/IP web server supplied web page for moni- tions” Proceedings of NISS, Beijing, China (2009) toring physical properties at a single sensor node in the sub- [3] Gi Heung Choi, Gi Sang Choi and Joo Hyoung Jang, way station. “A Framework for Wireless Sensor Network in Web- based Monitoring and Control of Indoor Air Quality (IAQ) in Subway Stations” Proceedings of International 6. Conclusions Conference on Computer Science and Information Technology, Beijing, China (2009) A basic framework for web-base information system [4] Ben Bronsema, et al, “Performance Criteria of Build- in VDN environment that can be applied to safety and ings for Health and Comfort”, Report of ISIAQ-CIB, health monitoring in subway station was suggested. Task Group TG42 (2004) Since the physical variables need to be closely moni- [5] Ki Won Song, Gi Sang Choi, Gi Heung Choi, and Jung tored in multiple locations in the subway stations, the Soo Kim, “LonWorks-based Virtual Device Network concept of distributed monitoring network need to be (VDN) for Predictive Maintenance”, International implemented. The suggested framework was designed to Journal of Applied Electromagnetics and Mechanics, deal with various communication media used in twisted Vol. 18, Nos. 1-3, IOS Press, pp. 67-80 (2003) pair (TP) local network, wide area IP network and Zig- [6] Gi Heung Choi, “Lonworks Based Virtual Device Net- bee wireless network. Wireless network needs to be work (VDN) for Predictive Maintenance”, Proc. carefully selected since its performance may be affected KOSOS Fall Conference, Samchuk, pp. 324-327 (in by the electromagnetic interference due to the power Korean) (2008) line of the train as well as the complexity of the struc-