John Hopkins

Moving carefully, Don retreats down the line to 46 meters.

Now totally unable to focus properly on his rebreathers controls, his safest option is to stay on his backup open circuit tanks.

But this will burn through his air supply, and with the time consuming ascent still ahead of him, he's going to need more gas.

Don reaches out for a cluster of cylinders, clipped to the line nearby.

As he does so, his stomach does a somersault.

When he is finally able to, he gingerly starts grappling his way up the line towards the next decompression stop.

Above, a figure moves down towards him.

A support diver is coming to check on his progress.

Rapidly, the news reaches the surface team.

Don needs urgent aid.

A tether is made to clip him to the shot line in case he loses consciousness, and a rotor is agreed to ensure at least one diver remains with him at all times.

But despite this, Don's situation remains dire.

It's been a couple of hours since he entered the water, but as he nears the surface, his decompression stops need to become longer and more frequent, meaning he still has more than 10 hours to go.

The climb is grueling.

Don's throat and stomach are raw from retching, and it takes all his strength to maintain his grip on the shot line.

But even as he edges laboriously closer towards the light and air, this strength is fading.

Too weak and dizzy to maintain a diver's usual horizontal position, which allows gas to flow directly into the lungs, Don is forced to breathe vertically.

Soon, every inhale is a painful effort.

Don is forced to press his regulator's purge button with each inhale, which helps to push a stream of gas into his lungs.

It's all that's keeping him alive.