In the 1960s the US Navy developed three undersea habitats, in order to experiment with saturation diving and to explore the possibility of humans living on the ocean floor. Of necessity, any group of people engaged in this pursuit would be separated from life on the surface, in some cases by days or weeks of decompression obligations. SEALAB I, II and II were progressively deeper and more complex habitats. Developing them was a technical challenge that led to many advances that we benefit from today. The experiments also provided an opportunity to study the psychological and physiological effects of isolation, and of long periods of breathing mixed gases under pressure.
The SEALAB experiments took place during the same era as the efforts by NASA to put a person on the moon, and received far less attention. Jacques Cousteau was interested in the project, and himself experimented with underwater habitats called ConShelf I, II and II. These habitats were far better publicised than the US Navy’s efforts, even though their aims were more modest.
Author Ben Hellwarth does not confine his attention to the habitats, but also provides a fairly detailed history of decompression theory and diving history. Like Neutral Buoyancy, SEALAB might provide a relatively painless introduction to dive theory for Divemaster candidates. In fact, this book reads like a thriller at times! Some photographs from the SEALAB projects are available on the US Navy website, and in this slideshow. To our modern eyes, the clunky and primitive appearance of some of the gear is a reminder of how pioneering the now 60 year old work to allow humans to live and work in the sea was.
If you’re interested in the history of saturation diving, I recommend this article, which covers some of the ground that Hellwarth does in SEALAB. If you want to see it in action, check out Pioneer (fictional movie based on actual events) or the series Deep Sea Salvage. You should also check out this article by Hellwarth, entitled The Other Final Frontier, and this podcast/radio show. If you are EXTREMELY interested in this subject but don’t want to read a book, try out this hour-long lecture video by Ben Hellwarth.
Yesterday I told you about a dive on Doodles, a reef in southern Mozambique, during our trip to Ponta do Ouro last month. Doodles has a maximum depth of about 14 metres. After forty five minutes’ dive time, my Suunto D6 began to register extreme depths (89 metres maximum), and to give various instructions about decompression ceilings and times, accompanied by strident warnings about exceeding my PPO2.
Suunto D6 after missed decompression
While annoying and potentially dangerous to lose the services of my dive computer mid-dive, it was also an excellent learning opportunity. Because I usually try quite hard to be safe and not to upset my computer, and dive within the conservative, recreational limits that I am trained for, I never get to see any of this behaviour from the instrument. (Fortunately the dive was shallow and I still had plenty of no-decompression time left so it was far from an emergency situation.)
After the dive, I soaked the computer in warm fresh water, and it gradually came out of dive mode over a period of about ninety minutes. During the course of this simulated ascent, the required decompression times and depths calculated by the algorithm were not adhered to, so the computer entered an error mode, which, according to the manual, indicates that “the risk of DCI has greatly increased.” (In fact, from all the beeping and flashing, I suspect the computer thought I was dead or close to it.) This error mode does two things: it disables the dive planning capabilities of the computer, and it locks you out of dive mode for 48 hours.
The D6 in gauge mode
I had never gotten the computer into this state before, so I was keen to see how it behaved when I took it on a dive in error mode. You can see in the photo above that I am wearing Tony’s Mares Nemo Wide (aka the flatscreen TV) to give me actual information about my no-decompression time, depth and dive time, but I took my D6 along for the ride. It is in gauge mode; this means it gives you only measurements, and is the setting a free diver might use.
The measurements available in gauge mode are: depth (18.4 metres in the photo above), the maximum depth you’ve been to on this dive (19.9 metres), an elapsed dive time (17 minutes), and water temperature (not shown) but it refuses to calculate a no-decompression limit for you. This would usually appear where the Er appears in the picture above.
Depth profile (with warnings)
For your enjoyment, here’s another screen shot of the dive profile from MacDive, with the warnings expanded. Click on the image to see it full size. It is clear that the first warning beeps I heard during the dive were because of elevated PPO2 levels. At 89 metres the device immediately put me in deco, and then as it “ascended” fairly rapidly, it gave a warning about oxygen toxicity (OLF or oxygen limit fraction as used in the Suunto algorithm) and an ascent rate warning. On the right, at about 10 metres, a warning is given that the depth is still below the required level to complete the decompression.
All the green circular icons appearing around the middle of my dive, where the computer thought I was at 35 metres, indicate that the computer registered that I surfaced, but not for long enough to show on the dive profile. Weird!
My D6 remained angry for 48 hours after the dive at Doodles; by this time, we had finished our diving for the week. I’m not sure whether the problem with the pressure sensor is a permanent one (requiring repairs, a service or a new dive computer), or whether it was just dirty or stuck and will have resolved itself next time I dive with the instrument. I’ll be wearing a spare dive computer when I do, just in case.
In this TED talk, self proclaimed “fish nerd” Pyle speaks about his work studying coral reef fish that live in the 100-200 metre depth range. This depth is too deep for scuba, and too shallow for submersibles, so Pyle pioneered the use of rebreathers (he was an early adopter, in 1994) to access this part of the ocean. This is a high risk pursuit, but the diversity and numbers of new species to be discovered here is stunning.
I first heard about Richard Pyle through Monty, who encouraged the readers of his Scuba Culture newsletter to check out an article Pyle wrote about an incident of decompression sickness when he was nineteen. The article is called Confessions of a Mortal Diver: Learning the Hard Way, and Monty is right – you should read it. Pyle actually mentions this incident right at the start of his talk. Watch below:
The four episodes of this History Channel series cover waves, tides and currents, predators, and pressure – all powerful features of the ocean that can be sensationalised (some more easily than others) and presented for shock value and as imminent threats to human life. Full advantage is taken of this fact.
This very American offering doesn’t boast the measured, mellifluous tones of Benedict Cumberbatch or Steve Toussaint as narrator, but the line-up of (mostly in-studio) guest narrators is quite impressive. Bruce Parker (The Power of the Sea), Susan Casey (The Devil’s Teeth and The Wave), David Gallo (scientist presenter of the TED Talk I mentioned here), Scott Cassell (student of the Humboldt squid), Richard Ellis (writer of a number of ocean history, art and sciencebooks), and Neil Hammerschlag (shark scientist) were familiar to me, as was big wave surfer Ken Bradshaw, from this article. The strange, uncomfortable way in which the studio narrators were filmed, with silent close ups interspersed with talking, was very annoying and must have been incredibly embarrassing to shoot. Or perhaps the cameraman took the footage when the narrators didn’t realise they were being filmed.
Unlike BBC documentaries, which tend to rely purely on incredible photography and fluent narrative to convey information, the History Channel favours a CGI-heavy approach that we encountered in Treasure Quest,Deep Sea Salvage, and also in the National Geographic SharkMen series.For the subject matter of this series – particularly the sections on waves, tides and currents – it was very appropriate and informative. The first episode, devoted to tsunamis, rogue waves and “monster waves”, made good use of CGI to illustrate the concepts as they were explained. The series was produced shortly before the Japanese tsunami of 2011 (there is a hastily tacked on “thoughts and prayers” disclaimer) and features interviews with a survivor of a tsunami in Samoa. I am fascinated by rogue waves – the whole episode could have been devoted to them but they don’t make for good television – we only have indirect evidence of their existence. Also, I could have done with more footage of giant ships battling storms, but that’s what youtube is for…
The least interesting and most irritating episode was the one devoted to the ocean’s top predators, which suggested that orcas are a serious threat to humans. As evidence, the cases of captive killer whales drowning and injuring their trainers at marine theme parks were cited. No mention was made of the psychosis that these whales suffer from as a result of confinement in a small, barren, completely unnatural environment. An incident in which orcas inexplicably rammed and sank a yacht in the Pacific Ocean is also described and re-enacted. Whether the orcas did what they did because they wanted to kill the people on board is highly debatable. There is also a half-hearted attempt to paint whales as potentially vicious killers, recounting incidents when sperm whales rammed whaling boats in the 19th century. More power to the sperm whales, I say.
The other dangerous predators were (predictably) white sharks, Humboldt squid, saltwater crocodiles and Australian box jellyfish. There was a small environmental message at the end of this episode, mentioning that squid will probably end up the top predators in our oceans if current trends – fishing out large predatory fish and global warming in particular – continue.
The third episode, on the immense pressures that objects in the deep ocean are subjected to, was very interesting to Tony and me as divers. A confusing interview with a diver whose brother got DCS on a wreck dive leaves (I suspect) much out. Were they even qualified divers? Why was he surprised that his brother felt unwell and confused as to the cause after he popped to the surface from 30 metres after a 30 minute dive?
The bulk of the third episode, however, recounts a 1981 experiment called Atlantis III in which three volunteers were taken in a saturation system to a simulated depth of 686 metres while breathing Trimix 10 (70% helium, 20% nitrogen and 10% oxygen). It took 31 days for them to decompress. The chief of the experiment, Peter Bennett, was the founder and former CEO of DAN. There’s a more information about the project here – worth a read (download the pdf slowly), and a briefer account here.
The series concludes with an episode on tides and currents, including rip currents. The massive tidal range of Morecambe Bay in the United Kingdom, is discussed at length. At low tide, up to 300 square kilometres of mudflats is exposed, and flooded again when the tide comes in. The guides who escort people out onto the mudflats when the tide is out seem like charming individuals – it is recommended not to wander around at low tide without local guidance. In 2004, the rising tide trapped and drowned 23 Chinese immigrants who were working the cockle beds – with such a large expanse of land to cover, the rising tide comes in at great speed. There is also a harrowing re-enactment of a father and his two sons getting washed out to sea in a rip current in Kauai that should make you think twice about swimming at beaches with warning signs on them.
You can get the DVDs here if you’re in South Africa. Foreigners, go here or here.
If you’re a Cape Town diver, and serious about enjoying the huge range of wrecks and reefs we have here, there are two Specialties that you should seriously consider.
One is the Deep Specialty, which qualifies you to go to 40 metres. (The depth it qualifies you to go to is actually less important than the skills you will learn on the course.)
The Number One cat helps Tony apply a Nitrox sticker to one of his cylinders
The other is the Enriched Air/Nitrox Specialty. Enriched air is ordinary air that has been enriched with extra oxygen. This reduces the nitrogen concentration, which is a good thing for two reasons.
When we breathe air under pressure, nitrogen is absorbed by our body tissues (particularly quickly by fat). While you’re at depth this isn’t a problem, but it becomes a problem when you ascend too fast and neglect to do the required safety stops or decompression stops. The nitrogen forms bubbles in your blood, brain and joints, and you will get bent. This can be fatal, and it’s a horrible way to go. You can think about what enriched air does for you in two ways: you get extended bottom time within the no-decompression limits, or a margin of safety because if you follow the dive tables for air when breathing nitrox, you will have absorbed less nitrogen into your tissues by the time you ascend. The risk of decompression sickness is thus reduced.
Nitrogen has a narcotic effect when breathed under pressure, and this can impair judgment and lead to all sorts of stupidity on a dive. Less nitrogen in the mix you’re breathing means less narcosis.
It’s not as simple as just putting more oxygen in your cylinder and jumping into the water, however. Oxygen is toxic when breathed under pressure (you just can’t win!) and can cause convulsions. At the bottom of the ocean, a convulsion is bad news. So while you are free to add oxygen to your breathing mix, your maximum depth is restricted by the richness of the mix you choose. Nitrox mixes are referred to according to the percentage of oxygen in the mix. Normal air has 21% oxygen: Nitrox 32 means that the cylinder has 32% oxygen in it.
The Nitrox Specialty is mainly theory – there are some formulas that you need to get to grips with, and you need to understand the two-edged sword that is enriched air. Once you’ve mastered the theory, you’ll learn how to use a Nitrox analyser, and probably do two dives on Nitrox.
As you dive more and more, your air consumption gets better and better. When you get to the point where your dives are limited by the no-decompression limits of air rather than the amount of air in your cylinder, the Nitrox specialty becomes extremely attractive. If you’re in the group of divers (such as older, or overweight) who are most at risk of decompression sickness, diving on Nitrox is a huge investment in your own safety. And finally, if you do repetitive dives (several dives in a day), diving on Nitrox will extend your total bottom time tremendously.
Diver Down: Real-World Scuba Accidents and How to Avoid Them – Michael R. Ange
Diver Down
This book should be compulsory reading for all careless, lazy, poorly-trained, slapdash or happy-go-lucky divers out there. In fact, for all divers.
This book is short with lots of sidebars (I don’t like these in books – they make it hard to read smoothly). Each chapter starts with an account of a diving accident (not all of them fatal). An analysis of what went wrong follows, as well as a short checklist of what you can do to avoid a similar fate.
I was at first reluctant to read this book because I thought it might scare me, but Tony devoured it and suggested I read it. It was disturbing, but didn’t give me nightmares. Michael Ange doesn’t write in a prurient or senstational manner – he just presents the facts. He has ample experience reviewing diving accidents.
Most of the time it was really simple things that caught people out, or a cascade of trivial compounding errors or problems. Often it was ego or over-confidence that led to the problems. Controlling partners or well-meaning parents who pressured their loved ones into doing things they shouldn’t also feature strongly.
The emphasis is on training, experience and common sense – every single thing you learn in your dive courses is vital. PADI and friends want to make diving fun and accessible, and they’ve pared down the manuals to be as concise and un-intimidating as possible… So EVERY SINGLE WORD counts. This is both a good thing (no scary huge textbooks) and a bad thing (you NEED to pay attention when you read and watch the DVDs and spend time with your instructor).
Dive briefings are also important. Your local Divemaster isn’t trying to dampen the mood by warning you not to surface without an SMB – he’s ensuring that you don’t end up out at sea without a signalling device, or with an unwanted Yamaha haircut. When the skipper and Divemaster speak they’re doing it out of a wealth of local (and that’s important) experience. Pay heed.
You can get a copy of the book here if you’re in South Africa, and here otherwise. If you want to read it on your Kindle, go here. If you dive, you should read it. And you should do a Rescue Diver course.
A cylinder, scuba tank, or dive cylinder as they are often called is a pressure vessel containing air under extreme pressure and in most recreational diving cylinders that’s all there is in it.
The air we breathe is made up of 79% nitrogen and 21% oxygen. An enriched air (nitrox) cylinder will contain just that: air, enriched with more oxygen, normally somewhere between 32% and 40% depending on the dive plan. This extra oxygen decreases the nitrogen content of the gas in the cylinder.
A recreation dive cylinder is not an “oxygen tank”. Pure oxygen, if breathed below 10 metres, can result in oxygen toxicity: this can kill you.
The most commonly used dive cylinder is a 12 litre and it has a working pressure of 232 bar (you have around two bar in your car tyres). Pumped to 200 bar, a 12 litre cylinder will have 2400 litres of air inside it (12 litres multipled by 200). In this part of the world (South Africa) a scuba cylinder is required by law to be painted yellow with a grey neck. An enriched air or Nitrox cylinder is required to be marked with an additional green band around the top, preferably so labeled.
Nitrox cylinders showing the green banded marking
Reference to an “oxygen tank” in recreational diving is just that, a cylinder filled with pure oxygen, painted black and white These are primarily for medicinal use in oxygen first aid, in treating decompression sickness or other emergencies. Their other use is or for very shallow decompression stops (6 metres or less) usually done by technical or deep divers. Oxygen tanks are also used (as in the picture below) for blending of enriched air mixes for Nitrox diving.
Correctly marked oxygen tanks at False Bay Underwater Club
If you want to talk about the cylinder of air that a scuba diver wears on his back while diving, the correct terminology (or the term that would be understood by most divers) is dive tank, cylinder or tin of sky (OK, that last one is not entirely serious).
