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HI-FOG Water Mist Fire Protection, 2004. Fire Protection Of Metro Systems. AOFST 6
The fire risks in urban underground transport systems or metros are amplified by the problems associated with mass evacuation of people in case of emergency. The primary danger is that posed by smoke, as this is difficult to vent in a controlled way from an underground space. Although most metro systems now operate no-smoking policies, a small minority of people disregard the rules and a casually dropped cigarette butt is the biggest fire danger. There is a particular danger if this occurs on an escalator where there is also the risk of fire from major mechanical failure. Fires can also occur due to overheating of electric cables or equipment in transformer & switchgear rooms, control rooms, garbage rooms, store rooms and retail shops. Fires can also result from accidents involving refurbishment work. They may also be deliberately started by an arsonist. Because of the dangers of smoke underground, the primary objective of fixed fire protection systems must be to rapidly extinguish or suppress a fire so that smoke is minimised and surrounding areas are cooled so that re-ignition cannot occur. Systems must be extremely reliable and ideally capable of frequent testing to ensure operational readiness. They should also not be people harmful or a danger to, equipment or the environment, whether set off in a fire or accidentally discharged.