Detonator (railway)

A railway detonator, (torpedo in North America) or fog signal is a coin-sized device that is used as a loud warning signal to train drivers. It is placed on the top of the rail, usually secured with two lead straps, one on each side. When the wheel of the train passes over, it explodes, emitting a loud bang. It was invented in 1841 by English inventor Edward Alfred Cowper.

Uses

Typical uses of detonators include:

A warning, caution or stop signal in dense fog, when signals are difficult to see

A warning of a train stopped on the line ahead by an incident or accident—the train crew are usually responsible for placing the detonators

A warning of ongoing engineering works ahead

When a signaller or other railway employee requires to stop approaching trains in an emergency

On a high-speed line, detonators may need to be placed on both rails.

Like all explosives, detonators can become unstable over time and must, therefore, be replaced regularly.

They are triggered by pressure, rather than impact. This makes them safe during transport, as they normally cannot detonate in a bag or storage container.

In Australia

Today known as audible track warning signals, or audible track warning devices, detonators are used to attract the attention of train crews when track repairs or an obstruction are ahead, or when a hand signaller is acting for a signal.

In Germany

Detonators were used where hazards had to be secured and there was no time for other signaling or if there was a danger that another signal might not be recognizable in time, for example due to fog or snow.