Improvement of voice alarm systems in underground stations

Voice Alarm systems (VA) are an essential part of subsurface underground station emergency and evacuation systems. Their main purpose is to assist in the management of emergency situations and evacuation procedures by providing key verbal instructions to the occupants. However these life-critical systems will be ineffective and even counter-productive if the speech messages broadcast are unintelligible. The 1987 Kings Cross underground station disaster and more recently the July 2005 bombings on London Underground (LU), raised the awareness of the importance an effective VA system for a safe and efficient evacuation procedure1,2. However following recent research3 appears that more can be done to improve VA system performance and therefore contribute to safer underground stations. Currently in many London underground stations and particularly on subsurface platforms, the announcements broadcast by the VA system are still not adequately intelligible and often do not reach the minimum specified performance target. This lack of performance could become a contributor in the development of a major disaster. An increasing demand for improved acoustic performance of VA systems in underground stations should not only seek to provide audible and intelligible vital instructions during an emergency. It should also aim at assisting passenger flows and providing necessary travel/passenger information with a high degree of clarity and acoustic comfort thus conveying an increased sense of well being and expected quality in the service provided. The process of designing and implementing satisfactory VA systems for underground stations is complex and depends on multiple interrelated factors, station design and operational constraints. The system performance directly relates to its electro-acoustic characteristics as well as the space where it is installed. Underground stations often present complex geometrical and architectural features which severely challenge the achievement of the desired performance. Awareness of the design environment and understanding of acoustic concepts, testing and modelling techniques can greatly assist the design to minimise the effect of inevitable external limiting factors and practical constraints. Despite the importance of VA systems in mass transit systems, there is very little research reported in the literature providing relevant knowledge, particularly in the context of real world underground spaces. Experimental data and practical design knowledge is not released by companies responsible for the design, installation and maintenance of VA systems. Moreover it was found that contractual or custom performance specifications are often not suitably set out which can lead to ineffective designs. The research outlined in this paper provides an insight into the practical aspects of electro-acoustic design of VA systems under real conditions found in underground stations. It also presents specific knowledge relevant to improved design and performance, and gives practical design guidance and recommendations. The paper also encourages through critical analysis to reflection the current underrated importance of VA systems in underground stations. It suggests that attitudes should be changed and proposes technical specification changes with the ultimate aim of ensuring improved system performance to contribute to safe emergency procedures.

ISSN 1478-6095; ISBN 978-906913-16-8