Anna’s story: “I was on my eighth or ninth dive, about five minutes in and at a depth of around 13 metres when I realized that my air was not coming out smoothly. I couldn’t think why this should be. I had checked my pressure gauge on descent and it had shown 190 bar. I switched to my octopus, but there was no difference. Soon the air became very thin.

It’s an adventure. You swim like a champion, trying to be as streamlined as possible and glide effortlessly through the water. Your heart rate is already at its limits and your breathing borders on hyperventilation. Your focus is on the sperm whale and its blow, which you can see just as you slide into the water. You are hoping to get the animal in front of your camera, but it is a bit of gamble.

When exercising the legs to keep them strong for scuba diving, it is important to develop muscle strength, endurance and flexibility. The legs must be versatile for diving activities, which place unique demands on the body.

At the Rebreather Forum 3 conference held in Florida in May 2012, a number of presentations were made which advocated the use of checklists as a means to prevent diving incidents from occurring, or at least reducing the likelihood of occurrence.