John Hopkins

The rebreather controller on his left wrist has imploded under the immense pressure at this depth.

Things have just got a whole lot more complicated.

Don must now manually insert gas into his breathing apparatus using another controller, and it's a tricky task.

At these depths, too much oxygen becomes toxic and can cause severe convulsions, which would likely prove fatal.

Even as he tries to delicately feed oxygen into the system, the levels of the gas in his rebreather grow dangerously high.

Don is forced to switch to his open circuit backup tanks.

But that comes with another problem.

Back to plan A. Don needs to get his rebreather stabilized soon.

If he can't, he may not have enough gas in his backup tanks to reach the nearest emergency cylinders nearly 100 meters above.

Drawing on his years of training, he performs a procedure known as flushing the loop, reducing the oxygen in his rebreather to safe levels so he can switch back to the machine.

Slowly, he gets things under control.

Crisis averted, for now.

But manually inserting gas and monitoring his levels is going to be a full-time job.

All his attention now has to be directed towards his own self-preservation.

And if he is having to focus on himself, it means he cannot focus on Dave.

He cannot go any deeper.

The bleak situation leads to a painful decision.

With one last glance of the unmoving light of his friend, John begins to head back to the surface.

Having gone deeper than he planned, he now needs to work out a new schedule for his ascent to limit his chance of getting the bends.

Also known as decompression sickness, this occurs when a diver resurfaces too quickly, not allowing enough time for nitrogen, another gas absorbed into the body through breathing, to be safely released.