Six detonators were stolen from the railway line near Worsley Road, Level Crossing in Knottingley sometime between 8pm on Saturday, 2 April and 12.30am on Sunday, 3 April.
Rail staff discovered the theft when they began work in the area on Sunday morning.
The detonators, which are safe if handled correctly, are designed to be triggered by impact and emit a loud bang when a train passes over them. In this instance, a number of them had been placed on the track by rail staff in order to warn rail maintenance workmen of approaching trains.
The detonators are described as small discs, approximately 5cm in diameter with two lead strips on either side.
PC Andy Jones said: "These detonators contain mild explosives and emit a loud bang when drivers pass over them, to warn track workers that a train will be coming their way soon.
"They could be very dangerous in untrained hands, particularly young children or teenagers who may see them as a source of fun or entertainment. Last year a teenage sadly lost their sight after a detonator accident so I can’t emphasise the dangers enough.
"We are obviously concerned for the safety of the individuals who have the detonators, regardless of their age, and I would urge anyone who has information that could help us with our enquiries to contact us as soon as possible."

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