Study and processing of the signals generated in tunnels

Protection of underground structures and tunnels is among of the problems of interest in many countries. These problems are related to the accidental (methane gas cloud) and intensional (terrorist) explosions and fires in underground structures such as subway and highway tunnels and mines. The consequences of explosions are particularly severe in confined spaces, where air-blast waves are amplified due to reverberations. Consequently, the mitigation of explosion effects in tunnels and other underground facilities is very important. Despite strict regulations for the prevention of accidental or deliberate explosions and fires in tunnels, the statistics of accidents and their consequences are dire. According to statistical data, around 1,000 people die each year because of methane explosions in coal mines [1-6]. Furthermore, the number of explosions in underground ammunition storage warehouses is steadily increasing. Therefore there is a need to reliable threat suppression system including threat identification module, which will also transmit wireless signal to suppression system activation module. This paper presents a first part of the investigation to develop threat suppression system and includes the selection of the operational parameters for fast and reliable signal identification associated with the following threats: hight energy explosions, methane explosions and fires. However, the fast and reliable identification of the potential threat is complicated by the presence of various (including ambient) signals inside the tunnels and underground facilities. This paper presents the results of the series of experimental studies aimed to isolate and identify various signal present in the tunnels with the aim to find the suitable frequency for fast and reliable signal transmission and processing. The data describing the characteristics of various signals in railway and transport tunnels were analysed and experimentally confirmed. The experiments also included the s- udy of the characteristics of signals due to the fire in underground structures. This paper also summarizes the research conducted for selection of the suitable methodologies for blast and fire detection in underground facilities. A comparative analysis of currently existing methodologies for blast identification has been also conducted. Based on reference search, the reliability and the time of response of currently deployed detection systems are failing to meet their requirements and therefore their functions remain limited. It was found that the reliability of the system is largely based on the selection of working frequency to transmit uncorrupted data. The selected working frequency will be used for creation of the emergency signal detection module, which will be one of the components of the proposed threat suppression equipment.