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  • Writer's pictureShaun Lewis


Last night I watched a fascinating TV programme about the building of the Forth railway bridge. The bridge is a remarkable piece of engineering. In the programme the narrator explained how caissons (steel watertight tubes from which water was expelled by compressed air) were used to allow the labourers to dig the bedrock of the river and build the platforms on which the towers are seated. It reminded me of a piece of research I came across whilst writing my book.

Divers have always faced the hazard of contracting ‘the bends’. This potentially fatal condition arises when divers return from deep to the surface too quickly. Atmospheric pressure is much greater deep in the water, causing compression of the body and bloodstream. As the diver returns to the surface, the body is decompressed and gases dissolved in the blood can escape as bubbles in the rest of the body, causing a painful and crippling or fatal embolism.

The condition was discovered in the mid-1800s amongst the workers building the Eads and Brooklyn bridges in the US. The bridge builders were working in caissons deep below the river surfaces. As a result it became known as Caisson Disease.

Fortunately, for Lieutenant Richard Miller and the crew of HMS D2, the condition was well understood in the early 1900s.

Diagram of a caisson of the Forth railway bridge

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