Michael McFadyen's Scuba Diving - Stupidity, the Cause of Most Dive Incidents
On Wednesday 3 September 1997, five divers went to dive the wreck of the SS Tuggerah off Royal National Park on the southern outskirts of Sydney. The Tuggerah lies at a depth of 47 to 49 metres.
There was a fair current running as the first two divers entered the water. The current was probably 1 to 1.25 knots from the north. There was also a strong wind from the south-west and this was increasing all the time. It was agreed that the divers would do a maximum of 12 to 13 minutes on the bottom to reduce the decompression required (due to the need of the first divers to hang on in the current while the second lot of divers were doing their dive). Agreement was also reached that the second group (of three) would enter the water about 10 minutes after the first divers slipped below the surface. All of the divers in the second group were using 88 cubic foot main tanks with 20 cubic foot pony bottles.
After checking that the first two divers were still on the wreck, the second group entered the water and with a bit of effort made their way to the anchor line. They each submerged as soon as they gained the rope and went down a dozen or so metres before checking on each other. No problems. The lead diver was the most experienced of the group with more than 1100 dives and over 240 dives deeper than 30 metres and more than 140 dives deeper than 40 metres. As he descended, he was working hard and found his Sea Hornet Command Air regulator a bit hard to breath so he adjusted the settings as he went. That was better. He also thought that the air he was using was a little bit off, but nothing to worry about. To assist him along, he used his hands to pull himself down the line.
Just as he saw the wreck, the first two divers passed him on the way up, their bottom time completed. They signalled everything was okay (if they had not been seen, the second group would have ascended almost immediately). As he approached the wreck he started inflating his BCD and noted that it inflated as normal, possibly even a bit quicker than usual. He hit the bottom soon after, just over three minutes after leaving the surface. This was more than twice as long as he normally took to get to the bottom on this wreck.
He looked back up the anchor line (just as he did a number of times on the way down) and saw one buddy. The other could not be seen. He was feeling quite good, suffering little from nitrogen narcosis. He then swam a few metres to the stern and shone his torch on the dozens of Port Jackson sharks that were lying everywhere on the sand. He then swam a few metres to where he had spotted a numb ray which he uncovered by blowing the sand off its back. He looked up again and saw the third buddy coming down (this buddy is always a lot slower descending).
Five minutes had passed since leaving the surface. All of a sudden, he noticed that his regulator was getting harder to breath. He checked his Aladin Air-X dive computer and saw that he still had more than 195 bar of air in his main cylinder. He took another breath and it was harder again. This was a problem, the air was running out. He signalled to the second buddy that he was out of air and began swimming towards him. As he did, he checked the reg by taking it out of his mouth and purging it. Only a dribble of air came out. He then grabbed his alternate air supply (not his octopus) and took a breath. It worked perfectly. He indicated to the buddy that this reg was working okay and that they all needed to ascend. The buddy quickly checked the valves on the two tanks to make sure that they were both fully opened. They were.
He then indicated to the third buddy that there was a problem and that they needed to ascend. He also indicated to the second buddy that he should quickly remove the anchor from the wreck so that they would not be stuck in the current while doing their safety stop. The second diver quickly removed the anchor and dragged it around to the down-current side and dropped it on the sand. As this went on, he and the other buddy started their ascent, keeping close together but also making sure the second diver was okay.
The three divers ascended without problem to the deco line where there was a 63 cubic foot tank as well as a 72 cubic foot tank of oxygen. Arriving at the deco stop, the diver then had time to think more about the problem. He again checked the second stage of his regulator and found only a dribble of air. He then tried the power inflator and found that it still worked normally. This was puzzling. He then reached behind and grabbed his octopus and breathed off it. To his amazement, it worked correctly. Why?
All of a sudden, a light went on above his head. What an idiot!!! He checked his Aladin Air-X and found that the contents of his 88cf tank had dropped from when he checked it on the bottom. No doubt, he was a complete and utter imbecile. He had solved the problem.
Instead of descending on his 88cf tank, he had used his 20cf tank and drained it dry in the seven minutes taken to swim to the anchor, descend and spend the first two minutes on the bottom. He had then grabbed the regulator for the main tank and used this for his swim to the anchor line and ascent. How had this happened?
As the divers had prepared to enter the water, the diver had put his hand down to grab the main reg which should have been hanging by itself at his side. Instead, he had grabbed the regulator connected to the pony bottle. Despite glancing at it, he did not notice the difference as up until a couple of months previously, this regulator had been his main regulator (all three regs were identical except for the colour of the covers). He distinctly remembered that the previous night when he set up his gear, he had put this regulator in a clip attached to the bottom of his BCD as normal. Somehow, the reg had come free and instead of grabbing the expected main reg, he had taken the pony bottle regulator.
What to learn from this?
- First, that no matter how experienced, how much care is taken, accidents can happen due solely to carelessness.
- A method of attaching regulators for second or spare tanks must be so unique that they cannot be mixed up in the heat of the moment.
- This is even more critical when using/carrying nitrox or oxygen for decompression (as you could suffer oxygen toxity at depth due to the high partial pressure of oxygen).
- It is also critical if using mixed gases for bottom mix, especially if the percentage of oxygen in one is far less than normal (as you could become hypoxic on the way down, especially if working hard in a current).
- At depth, thought reasoning is impaired due to nitrogen narcosis, no matter what you may think (notice how the diver could not solve the problem on the bottom but did immediately he got to the five metre mark).
- The importance of being correctly equipped when diving at depth (that is, carrying spare air, although in this case, of course, it did not make any difference and in fact contributed to the incident).
- The importance of buddy pairs when diving, especially at depth.
- The importance of diving with very experienced and correctly equipped divers.
- Do not dive beyond your experience level, because accidents do happen and it is important to be able to respond appropriately.
- Finally, that an experienced diver, when confronted with an emergency, can react calmly and correctly.
To end, who was this idiot? Me of course. I have now attached a cover to the mouth piece of the regulator of the pony bottle which is required to be removed before it can be used.