(1) Detonators or fog signals are appliances which are fixed on the rail and when a locomotive or a vehicle passes over them, they explode with a loud report so as to attract the attention of the locomotive crew.
(2) These are used when the line ahead is intended to be protected on account of any unusual incidence or accident and when either a competent railway servant is not in a position to initiate ' railway emergency call' on mobile radio and display amber flasher light or they are not provided.
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(3) These are also used when the visibility of signal is impaired so as to indicate to the loco pilot of an approaching train, the locality of a signal when any other "fog safe device " is not provided;