When trains come to rest in a tunnel, considerable quantities of heat can be transferred to the tunnel environment from the train equipment and passengers. This heat, together, with the moisture generated by the respiration of passengers can cause the temperature and relative humidity to rise to unacceptable levels. Further, in extreme cases, the carbon dioxide introduced into the interior of the train by the passengers can lead to uncomfortable or even unsafe conditions within the vehicles. The problem is dependent on the number of passengers and can be critical during the height of summer when air at high ambient temperature enters the tunnel. A computerised prediction method has been developed and is applied to simulate the conditions that develop inside a crowded train immobilised in a tunnel on a hot summers day. The predictions are discussed in relation to comfort and safety criteria for temperature, humidity and carbon dioxide concentration.
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