Exploding for Safety


Explosive safety devices for use in poor visibility, emergencies and to protect engineering works. . . . . . .


A Great Western Railway detonator fixed by two lead clips to bull-head rail. Photo: Mike Peart’s collection.

Detonators, or “Signals, Railway Track, Explosive” as we’re supposed to call them now, have been a feature of railway safety for over 180 years. These explosive devices fitted to railheads are still available to protect unsafe lines in cases of accident and other incidents, engineering possessions and temporary block working arrangements.


Detonators have a long history. In 1841, inventor Edward Alfred Cowper devised the explosive railway detonator for clipping to the rail head as a warning signal in fog. By 1844 they had been approved for widespread use. The press at the time promoted them to reassure the new breed of rail traveller. Described as detonating compound packed in a small circular box with flanges to fasten it to the rail, a train passing over one would produce “a tremendous noise” - a warning for an immediate stop. It was fixed to the railhead not less than ½ mile from the obstruction by means of a flexible lead clip. There was also the “fusée”, a flare-type firework which was lit by a sharp blow and placed in the four-foot. They would burn for about 15 minutes to protect any following trains from an obstruction ahead. Fusées were supplied to train guards in a long tin carried in the brake van.


By 1898 detonators were nine shillings (45p) a gross. A major manufacturer was Thomas Jenkins & Co at Sparkbrook, Birmingham. Their works was a building where the metal components were made and series of small wooden sheds well-spaced out about 50 or 60 feet apart across a large area of open field where the explosive materials were handled. If an explosion occurred, only one shed would be involved. Components were stamped out, assembled and lead straps soldered on before being taken to the sheds for the addition of the explosive material. In each shed, two men worked on the most dangerous part of the process by adding explosive powder and closing the cap. There was a partition between each of the two workers with a one-foot square hole through which the detonators could be passed for the next stage. A tray of water on the floor caught any explosive material and made it harmless. Each detonator was waterproofed with several coats of varnish before being labelled and sent to customers. Correct handling and storage of detonators was important. They had not to be roughly handled and had to be kept dry away from damp and steam.


Kynoch & Co of Birmingham Lion Ammunition Works was another manufacturer. Their range had different sizes, usually 1½, 2 or 2¼ inches in diameter, with the smaller sizes for underground lines. Their versions consisted of a base-plate with a strip of six inches of flexible lead to make fixing to the rail effective. Inside the detonator was a piece of iron with nipple projections to set off the black powder (gunpowder) within the tin-plate cap when crushed. A detonator might contain between 80 and 140 grains of black powder. The base-plate was crimped over the edge of the tin-plate cap before the detonator was painted and varnished to keep the contents dry. The date of manufacture was either stamped on or shown by a colour code. Oldest stock was used first, provided it was still in date and not affected by damp or rust. Batches were tested by immersion in water for between 24 and 60 hours before being run over by a light wagon. Another test involved throwing detonators high into the air to ensure they wouldn’t explode when falling to the ground!



An early 20th century lineside mechanical detonator placing machine with fogman in attendance. Photo: National Railway Museum.

Distances at which warning detonators should be placed were set at varying rates by different railway companies. For example, in the case of a blockage, one detonator would be fixed ¼ mile from it, then one at ½ mile and two at ¾ mile. As line speeds increased, so did the distances needed to place detonators. By 1977, protection of obstructions relied both on the track circuit clips carried in all trains and the use of one detonator at ¼ mile, one at ½ mile, three detonators 20 yards apart at one mile or three at 1¼ miles if the line speed was over 100 mph. This, of course, depended on the luxury of firemen, guards and others having enough time to cover the distances to the rear and in front of an obstruction in an emergency.



The business end of a detonator placing machine with two detonators located on the railhead.

As speeds and line occupancy increased, fog and falling snow posed threats to safe running and timekeeping. Platelayers started to be used as fogmen to work at particular locations when needed. This was a way of keeping platelayers usefully employed when they couldn’t do their usual work. Fogmen were allocated to one signal where they stood guard from a sentry box, hut or pit with a coal fire in a brazier or grate. They had a case of detonators, a handlamp with white, red and green aspects, and red and green flags. It could be cold work so they received a heavy overcoat to wear for a shift that could be eight to ten hours or more. The fogman’s task was to place detonators, usually two at a time, on the rail when the signal he was monitoring was at “caution” or “danger” and keep the handlamp aspect ready to change to green for a cleared signal when the detonators would be removed, or red for a “caution”. A driver passing over and exploding detonators at a distant signal would see the red light and proceed at caution to the home signal. In some locations the job became mechanised with detonator placing machines operated by signal box or lineside levers. On no account could fogmen leave their posts unless they were relieved by someone else, and stationmasters had to arrange for them to receive tea, coffee or cocoa along with something to eat at the companies’ expense. Tempting though it might be, intoxicants in any form were absolutely forbidden!


Mike Peart



[Mike Peart is a former railwayman on British Railways (Western Region). He is co-author of Volumes 3 (Freight Marshalling Yards), 4 (Level Crossings) and 5 (Train Detection and Control) of the “History & Development of Railway Signalling in the British Isles” series, and Trains of Hope”, all published by The Friends of the National Railway Museum, York. He’s been an active Friend of the NRM since 1994 and was one of the four “schoolboy” founder members of the Great Western Society (Didcot Railway Centre) in 1961 and its Honorary Secretary for several years.]



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