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Safety and training

Holborn Gas Explosion, Dec 1928

The Holborn gas explosion (1928) : London street reduced to rubble

In the early hours of a December morning, 1928, an explosion blasted through almost half a mile of solid tarmac reducing one of London's main thoroughfares into a twisted river of rubble. It was a powerful demonstration of the dangers posed by the underground network.

Some years before the Post Office had bought a disused tunnel, built to transport parcels from St Martins-le-Grand to Euston Station. The Post Office used it to run cables through the heart of central London.

Gas frequently seeped into the empty passages and it was standard practice for all engineers to release any gas before working underground. On this fateful morning however, an explosion rocketed through the chamber as soon as an engineer had climbed through the manhole cover, before he could switch on the gas dispersion pumps. It was closely followed by another devastating blast.

Half a mile of road collapsed, shops and cars were badly damaged and the engineer sadly died from his wounds.

GPO gas safety poster, 1949

Hazards of the job : keeping out of danger

Facing hazards is an everyday part of the job for telephone engineers working underground, meaning that accidents are occasionally inevitable. But in most cases, following the basic rules will keep staff out of trouble.

Flooding is problem - but normally one that can be seen well in advance. Afterwards, and the rule is don't do anything until the water is cleared.

Asphyxiating gas can creep up unawares, which is why engineers use gas indicators. Explosive gas can ignite from a spark from a blowtorch or soldering iron, but again the right detector will avert any risk of explosion.

Electric shocks are rare. The telephone network uses mainly low voltages, which present few risks. Problems can occur when wire come into accidental contact with power wiring, so staff must always be on their guard.

Varley four-wire lightning protector : no nasty shocks

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Electric current surges caused by lightning were (and are) a major problem for telecommunications operators, posing a serious potential danger to users.

There were many attempts to resolve the issue in the middle of the 19th century, with varying degrees of success. This is one of the more interesting ones. Looking like something out of Dr Frankenstein's laboratory, the device was connected between incoming lines and the apparatus.

If lightning struck near a telegraph line, a spike or surge of electricity could run along the line. When this reached the lightning protector, the device diverted the pulse directly to earth, which neutralised the danger, leaving the apparatus and operator safe in one piece.

fun and games

Can you beat our games? Explode equipment to see what's inside, hear the changing sounds of telecommunications, see how telecommunications designs have changed over time or send an e-postacard.

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The UK's first permanent gallery dedicated to the history of information and communication technologies opens in the new Information Age gallery at London’s Science Museum.

audio history

Take a trip down memory lane with extracts of the interviews which have been recorded as part of the Connected Earth oral history programme.

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