Deep dive

Plan your dive and dive your plan

Three divers approached me at the dive centre one day, requesting I take them to a dive site where they could dive to 60 metres. They wanted to test some new equipment configurations. Two were certified advanced Nitrox divers, qualified deep technical divers and had made several dives to over a hundred metres… in a lake. The third diver, like myself, was qualified to dive to 40 metres.

So we draw up a plan: they will dive to 60 metres, spend 6 minutes at that depth, ascend to 50 metres and spend 5 minutes there, then ascend to 40 metres 5 minutes thereafter and so on until the reached 6 metres where they would switch to pure oxygen to reduce the deco stop time as the current at this site is strong. The third diver and myself would meet them at 40metres.

Using a software program called V Planner we calculated that including the descent time and ascent times for each stage, at a controlled rate, we would enter the water precisely 16 minutes after they started their dive and we would meet them at 40 metres. We would then all be together for the next 30 minutes, ascending with them to their 6 metre safety stop, ensure they had both switched to pure oxygen and then leave them and return to the boat.

The plan was that we would spend 6 minutes on our descent to 40 metres and all four of us would reach 40 metres together. They were made to clearly understand that should they have a problem at any depth deeper than 40 metres we would not be able to help them as we were diving 12 litre steel cylinders on a Nitrox 32% mix, limiting our depth – and what’s more we did not have the qualifications to go to 60 metres.

We discussed the plan in great detail and everyone was set. A red SMB would be hoisted if they experienced any difficulty and a yellow would be released once we met at 40 metres.

Mistakes happen

We started our descent on time, and watching my dive computer and timer I descended at the agreed rate. My buddy, however, did not. He descended way too fast. Believing that they would be in control of their dive he descended very fast and joined them, ahead of schedule at a depth of 55 metres. They were 3 minutes behind schedule as they had struggled to come to terms with the ocean current. Now we had a problem. I waited at 40 metres, but they arrived late, and this meant I would risk going into deco before we left for the 30 metre stop.

At this point my buddy ran out of air. He was closer to the deep divers as he was reading their slates, so he grabbed the first regulator he could see: the deco tank regulator, filled with pure oxygen. At depth oxygen is toxic and can kill you in a matter of minutes. I grabbed it out of his mouth, so he grabbed my regulator out of my mouth as he was now starting to panic. He was holding onto me so tight I could not reach my octo so I reached for the octo of another diver. So here we were three divers locked together at 40 metres, each with a regulator in our mouths that belonged to someone else. I managed to get him calmed and off my cylinder and onto the octo of the deep diver with the most air. Now back to normal, we started our ascent and did the required safety stops, reached the 6 metre stop for them to switch to oxygen and headed for the surface. I reached the surface with 10 bar in my tank.

Deep dive
Ascending from the almost disastrous deep dive on Atlantis in Ponta do Ouro. Note the hang tank of pure oxygen.

My buddy had been to 55 m on a Nitrox mix of 32%. The maximum safe depth for this blend is 40 metres. He had almost sucked on a cylinder of oxygen at 40 metres, this is a lethal dose at depth. Mistakes happen. Be meticulous with dive planning, rehearse your incident scenarios and make sure you dive your plan.

Published by

Tony

Scuba diver, teacher, gadget man, racing driver, boat skipper, photographer, and collector of stray animals

Leave a Reply