As Christopher Boodram squinted in the darkness trying to work out where he was, he knew he was in trouble. His eyes were burning with toxic fumes.

The last thing the commercial diver remembered was struggling to repair an oil pipe in the Caribbean sea.

Now, he was lying flat on his back deep in thick black liquid and had to crane up his neck to reach the tiny pocket of air above him to breathe.

Reaching out with his hands and feet he found he was surrounded, encased, by a tube of corroded metal barely wider than his shoulders.

He tried to sit up and scraped his head on the harsh metal. That was when he knew for certain where he was: he was trapped inside the pipeline – somewhere deep beneath the waves.