Getting started – the human echo-sounder.
I was twelve years old and it was the day before the summer holidays. A year or so earlier, along with most of my mates from juniors, I’d failed my eleven plus so we were at a fairly decent secondary modern and Ron and I were planning what to get up to during the coming weeks.
“You coming swimming with us O?”. I was O’Neill to the teachers but just ‘O’ to my mates.
“Sorry mate, can’t swim”.
“Course you can swim; how can anyone not swim?”. He continued “look, we’re all going to slimy plankton’s; they open up their swimming pool to everyone in the summer holidays; c’mon O, it’s somewhere to mess about, what else are we going to do?”. Ron had a point.
Simon Langton boys school was the local grammar. Why they opened their gates to us oiks remains a mystery. And then we showed our gratitude by calling the place ‘slimy planktons’. Thanks to Ron though, that summer I learnt to swim, joined the water polo team and nearly drowned.
Sea Hunt and The Undersea World of Jacques Cousteau were TV programmes that fired up my early imagination, so at the age of fifteen, I joined the Canterbury Branch of the British Sub-Aqua Club. And so it was, armed with triangulation marks from a local dive shop, at 09:00hrs on Friday 7th July 1978, we were searching for the wreck of the Kantoeng. The Kantoeng was a dredger sunk in fifty feet (we were both imperious and imperial in those days) of water about half a mile out of Fowey harbour.
Our diving kit was fairly rudimentary; air capacity was restricted and decompression calculations – the stuff that prevented us from getting ‘the bends’, were worked out manually from tables based around maximum bottom time with no allowance for pratting-about getting to the bottom in the first place, which is why the assembled brethren decided that I should hold onto the anchor and with just a lungful, jump over the side and check if we were on the marks. One of the rules of freediving is that you don’t mix freediving with scuba; some years later, breaking that rule did indeed lead to me getting bent. But on that sunny day in 1978, before the rules had been invented, all went well and on the 3rd attempt I landed, still clutching the anchor, feet first, straight into an enormous dredger-bucket full of startled fish.
On a slightly serious note
‘take a breath…’ consists of a series of lighthearted anecdotes and observations about the pursuit of freediving. We will explore both the thrill and a smattering of the science associated with breath-hold diving, but this is definitely not a ‘How-To’ guide. Some of the exploits described herein could be viewed as risky bordering on downright stupid, therefore, just in case you are tempted to ‘take a breath’ and indeed, ‘make it a big one’, please read the next bit – it is important.
Pay attention
Snorkelling around a shallow reef and enjoying the view from the surface is fine. Just make certain that someone is keeping an eye on you. If you are unfamiliar with your surroundings, on holiday for instance, be vigilant; that fish or coral head may look beautiful, but touch it and it may sting you badly enough to ruin your holiday. And, if the reef you are studying starts to whiz by a bit quick you are being carried along by the current, so make certain that it isn’t carrying you out to sea.
Get a buddy
If you decide to take a breath and venture below, YOU NEED TO BE WITH A BUDDY. There are some very real dangers associated with breath-hold diving and if something goes wrong, you need to have a buddy on hand to keep you alive.
Get trained, or at least read a good ‘How-To’ guide.
If you intend to venture into the deep, then get properly trained. The sport of freediving is gaining in popularity and there are a number of organisations that will impart the knowledge needed to experience the abyss in relative safety.
Respect the locals and stay out of the food chain
One of the benefits of freediving is that the indigenous will view you as just another big fish; treat them with respect and they will probably treat you the same way. There are however, some very big fish out there and while scuba divers can observe potentially dangerous sharks from the relative safety of reef and seabed, a snorkeller’s legs dangling from the surface can present a tasty morsel that is just too irresistible… time for a couple of anecdotes…
I met Dave in 1995. We were on Anze Lazio beach in the Seychellois island of Praslin. Dave was a non-swimmer so he wore a life jacket and bobbed about close to the shore. There was plenty to see in the shallows; indeed, my wife Glenys quite enjoyed snorkelling about in this zone until she accidently disturbed a stingray – strewth, you’d have thought she was being pursued by a great white; there was an ear-piercing scream, followed by frantic finning as she hit the beach like a torpedo! Anyway, back to Dave. Dave had observed me snorkelling out from the beach, ducking under the safety rope and finning well out from the shoreline. I was on my own out there, but the location seemed safe enough; there was little current, the depth was a comfortable seven metres or so and there was a lot to see among the tall rocky outcrops, including hawksbill turtles. Back on the beach, Dave came over to ask what it was like; his disappointment at not being able to join me was palpable, so I offered to tow him out and let him observe from the surface. This was one of those occasions where witnessing someone else’s enjoyment and excitement dramatically enhances your own experience. The deal was that the instant Dave felt uneasy or he’d just had enough, I would drag him in. In the end I had to override his desire to stay out there as I was starting to resemble a wrinkled prune.
When we visited the Seychelles there were no recorded shark attacks, or at least none that anyone was owning up to, but in 2011 there were two fatal attacks just twenty metres off of Anze Lazio beach.
Makes you think…
…on the other hand, although barracuda look scary, the huge one that regularly accompanied me during afternoon snorkels off of the Bahamian island of San Salvador probably just saw me as another big predator. It stayed disturbingly close, just a few inches from my fins, no doubt assuming that eventually I’d kill something which it would then share with me. My piscine dive buddy remained disappointed.
My point is that although there is no reason to be afraid of the marine environment, developing an understanding of it and maintaining respect for it will keep you safe and enhance your enjoyment. If you intend to visit somewhere new and go snorkelling, check out the location beforehand via the internet and seek local knowledge when you get there. The marine environment is changing, partly through the adverse impact of humanity. The practice of feeding sharks and stingrays for the benefit of tourism risks changing the balance within the food chain and may well be exposing people to greater risk. On the other hand, swimming with a huge barracuda when you have an understanding of its normal behaviour is a privilege.
Getting into the zone
As this is about a subject that fascinates me, this literary endeavour should write itself, but before we get started there is an obstacle to overcome. I need to both fire up your imagination and ensure that you are completely relaxed, stress free, safe, warm and securely cocooned in a web of tranquillity. To achieve this zen-like state, I need you to sit cross legged on the floor (a half lotus is handy, but not essential), shut your eyes (you’ve spotted the problem here), breathe deeply and try to reduce your heartrate to a level that is just – only just, conducive to staying alive.
To get over the problem of you reading this with your eyes shut, I need you to read down as far as ‘this is your final breath, so you’d better make it a big one…’ and commit the gist of it to memory…
…ok, let’s assume that you’ve read from here down as far as ‘this is your final breath, so you’d better make it a big one…’, so this is me inside your head and you sitting on the floor with your eyes shut, concentrating on your breathing and the blood coursing through your body.
- Just breathe normally and calmly. Adrenalin is not our friend here, so relax; you feel warm; you feel safe; you are completely calm.
- Try to balance your body evenly over your crossed legs and your bum.
- Merge your consciousness into the darkness in front of you; try not to think about anything at all and if you cannot achieve this, then imagine a gently flowing stream, or corn heads wafting in a warm summer breeze.
- Now deepen your breathing; as you breathe out, pull your diaphragm up and empty your lungs as completely as you can; as you breathe in, draw your diaphragm down and fill your lungs to their capacity. As you repeat this, the volume of each exhalation and inhalation will increase as you stretch those intercostals and push your lung capacity to its limit.
- Now you need to concentrate on honing your rhythm. Exhalation should take twice as long as inhalation; this will further aid your relaxation. I really do need you with me on this, so keep going steadily, in for the count of six and out for the count of twelve; in…out… in… out. You’ll be rocking gently backwards and forwards with each breathing cycle, balanced evenly on your crossed legs and bum.
- Then, breathe in, and in, and then breathe in some more; you think that’s it, it’s not, fill those cheeks and force their contents down into your lungs… this is your final breath, so you’d better make it a big one…
Ok, you’re mine now; I have your imagination, let us proceed…
- Hold onto that last breath. This is important. Relax though, everything is completely fine.
- Open your eyes; it’s fairly dark, but you can see a dim circle of light some way in front of you.
- Look to your right and do please hang onto that last breath; about half a metre from your right elbow is a wall of rock. Now look to your left – ditto.
- Look up; there’s a rocky ceiling, also about half a metre above your head. Trust me though, everything is fine, but do please hang onto that final breath.
- Look down and keep holding that last breath; you’re sitting on white coral sand.
and then it gets very dark…
Oh, and by the way, I should probably have mentioned it earlier, but there is fifteen metres of water above your head, so if I were you, I’d carry on holding onto that last breath while we work out how to get you out of this self-inflicted predicament. Firstly though I’d like to explore the benefits of diving on a single breath and consider some of the physiology that’s going on, which I’ll attempt to do through a few more anecdotes and observations.
Sorry, I almost forgot, you are still holding your breath. For the time being, we’ll leave your id – the part of your mind in which innate instinctive impulses and primary processes are manifest, sitting cross legged on the floor holding its breath. Rest assured though, I’ve been through the same preparation that you have just practiced and sat twenty metres inside a coral cave situated fifteen metres below the surface of the Caribbean Sea with only one lungful, so no worries, everything will be fine, but for now…
…breathe, breathe, breathe…
Over the years I’ve struggled to answer the question; what’s best, freediving or scuba? You can get to places with an aqualung that are unreachable on just a lungful, stay there, have a good look around and take some photos. On the other hand, if you’ve got access to a coral reef and you’re not blowing bubbles, the indigenous will treat you the same as any other big fish. And, although I appreciate that this will not be everyone’s ‘cup of tea’, there is something indescribably (although I am going to try and describe it later) satisfying and life affirming about achieving the physical and mental state necessary to calmly drift into the abyss.
Why freedive?
1. The coral reef
Thudufushi is a small coral island located on the edge of the Maldivian South Ari Atoll and although I didn’t know it at the time has one of the best ‘house-reefs’ in the world. Glen and I had chosen this venue for the usual holiday stuff – sitting in the sun with a good book, a few cold beers, someone else to do the cooking and, for me, the chance for some scuba diving. As we stepped from the seaplane onto a wooden jetty and gazed down into coral encrusted fish soup, the beauty of it was stunning. During that holiday I donned scuba clobber just the once and to be honest, it was like eating a sweet with the paper on.
I bumped into Tony ‘One’ (Tony ‘Two’ comes later) on ‘Thud’. Tony was keen to try snorkelling so we spent a fair amount of time together perched on a concrete block at the edge of the drop-off, chatting and relaxing while readying ourselves for excursions to the point where the reef met the sand, some twenty metres below. Standing on the concrete block wearing nothing but ‘budgie-smugglers’ and a t-shirt, the cleaner-wrasse soon discovered that human bum-cheek made a tasty alternative to dead fish skin and parasites, so ‘breathing-up’ exercises were best completed on-the-move. Coral atolls occur in warm seas; the sun shines, so the light is good and most of the best things to see are found above twenty metres. Come with us…
Lying on the surface, we look down into the clear water at a myriad of fish. Duck down to a coral head and the aggressive little damselfish dash from their lairs, popping and clicking, sizing up to us for a fight; wiggle a finger towards them and they beat a hasty retreat, then they turn-about and charge again. Parrotfish are dominant; they graze on the dead coral, crunching away at the algae and squirting remarkable quantities from their back-ends (yep, coral sand is mostly fish-poo).
At just a couple of metres below the surface, the top of the reef, where it meets the drop-off, is a comfortable depth, so we duck under and glide past the edge, following the near vertical wall down. On the way we spot a large grouper resting in a hollow in the reef. We are neutrally buoyant at this point, so we glide in effortlessly behind this hulk, who flashes us an irritable look of displeasure and then moves away just far enough to give us room at the cleaner-station. The cleaner wrasse are onto us in earnest now; we open our mouths and in they come for a pick about our teeth; given the absence of gills, they nip at our ears instead. This is becoming a bit unpleasant, so we carefully close our mouths and move away leaving the clean-up party to resume their work on the grouper, who immediately reclaims his spot.
We are negatively buoyant now, so we glide effortlessly downwards, checking out crevices for moray eels and neatly swerving by an exquisite but highly venomous lionfish…
We keep one eye out into the blue for any patrolling reef sharks, with the other on the lookout for ‘Nemo’ as we continue to accelerate. Nearing the sand at the foot of the reef we spot the distinctive markings of a stingray…
That’s enough of the sightseeing; now for some proper excitement…
Why freedive?
2. Wreck diving without an aqualung
If wreck diving is on the agenda, then an aqualung is usually de rigueur. Not necessarily though.
Wrecks are fascinating places to explore and, depending on how the wreck occurred, they command and deserve the utmost respect. To visit the aftermath of a torpedo attack, see the bent plates and consider the terror and potential for loss of life, is both moving and humbling. Some wrecks though are a bit more prosaic in origin.
Margo and I met on a dive boat out of Cayman Brac; we enjoyed several marine liaisons, including a couple of visits to the wreck of the MV 356, a Russian Koni 11-class frigate. In 1996, the ship was renamed ‘Captain Keith Tibbetts’ in honour of a local dive operator, and then it was scuttled at the edge of the Cayman Trench specifically for the purpose of diving. It is a worthwhile dive, but as I ambled through and around it with Margo, it occurred to me that it would also present a safe and enjoyable snorkel. I put this to the dive master, who readily agreed, as a member of his dive team regularly accompanied visiting dive groups sans diving clobber. Our first visit to 356 was relaxed; the divers chatted, did buddy checks and generally enjoyed the camaraderie that you expect on these expeditions. Not so the second dive…
I had made my mind up to snorkel and so Margo buddied with one of our regular dive leaders. The other divers were in an organised party, accompanied by their own dive master. Some big egos were getting a serious airing. Conversations included “…when I was advising Steven (Spielberg), recently…”. And “…when I’m not diving, I cycle and the other day I was chatting to Lance (Armstrong (he was still popular then!)) about gear ratios…” And then “…of course I usually concentrate on technical mixed gas diving, its more exciting”. And while this was going on, they unpacked and assembled some of the most expensive and comprehensive dive kit I had ever seen; dry suits, redundant air supplies, twinsets (double air cylinders, not outfits that go with pearls!). I helped Margo into her basic but perfectly adequate kit and took up a relaxed position atop the life raft, with mask fins and snorkel at the ready. As Margo and I relaxed quietly with our own thoughts, one of the ‘experts’ ambled over and suggested that I should learn to scuba dive; I smiled and nodded, Margo said nothing.
During the dive, apart from Margo and her buddy with the video camera, most of the other people I met in and around the wreckage, seemed surprised to see me. It was not particularly challenging on just a lungful; there were two mooring buoys fixed to the wreck, it was only ten metres down to the conning tower and twenty metres or so to the seabed amidships. The bow of the wreck rests at thirty metres, precariously close to the edge of the Cayman Trench. I enjoyed gliding along the deck, free from the encumbrance of dive kit and even took a quick look inside; serious wreck penetration was out of the question though, especially with a load of over inflated overweight ego’s threatening to block the exits! That evening in the bar the dive crew showed the video; I heard someone say “…did you see that English idiot in the shorts and t-shirt?”.
Hopefully that covers the why, now we’ll consider the how’.
The Mammalian Diving Reflex
I met Tony ‘Two’ on Salt Cay, a small island in the Turks and Caicos. Tony was on his own and I was with Glen. Tony and I teamed up for diving and the three of us went whale watching together; it was a great trip. I did worry about Tony a bit though; the recommended maximum safe depth for compressed air is fifty metres and Tony decided he’d have a go at sixty; on that occasion I kept an eye on him from ten metres away; a couple of years later the pair of us reached sixty-five metres in Bonaire – plonkers!
While we were on Salt Cay I also did some freediving. Freediving is soundless; scuba on the other hand is noisy due to the whooooosh on inhalation and bubblywubbly on exhalation, which is why I heard the beautiful song of the humpbacks and all that the scuba divers could hear was whoooosh and bubblywubbly. Anyway, back on the boat, relating my tale of whale-song piqued Tony’s interest and it was then that I hatched a plan to bring him up to speed on the freediving front.
Before leaving Salt Cay Tony said he’d organise a trip to the Red Sea for us, which left me to sort out a trip to HMS Dolphin, the submarine escape training tank (SETT) at Portsmouth. I’d visited the SETT many years previously with the diving club, but then, to my knowledge, it was not possible for a civilian to have a go in the tank. I did however witness an RN instructor freediving to the bottom. Nowadays however it’s a different story, so I booked the pair of us in for a weekend freediving course.
The SETT is basically a thirty-metre-deep tank with a submarine escape hatch at the bottom. As part of their training, submariners are shoved in at the bottom and blasted up to the surface. On a freediving course, you get in at the top (having carried out the relaxation exercises) and over the course of the weekend aim to extend your depth capability until you can get to the bottom, and hopefully, back up again.
Initially Tony was relaxed about it. And then the literature turned up! The course organisers sent us a pack of information which included various exercises and practice schedules aimed at improving our breath holding capabilities; thus we would be able to maximise the opportunity that the SETT would afford us. I recall getting a phone call from Tony; he’d received his pack and had a go at the breath holding exercises, but the best he could manage was twenty seconds. He was seriously concerned about looking daft.
The point is of course that most of us never need to hold our breath (notwithstanding anyone sharing a tent with my mate Jeff after a few pints and a curry that is), and Tony was a smoker as well, which didn’t help (and thinking about it, it’s just as well that Jeff doesn’t smoke!). Anyway, I tried to reassure my old mate and he, to his credit, pressed on with the exercises.
We met at our digs in Portsmouth. It was the day before the course started and Tony was still unable to hold his breath for half a minute, so it was with some trepidation that next day we presented ourselves to the course instructor. The weekend consisted of classroom work, breathing and yoga style exercises together with time in the tank. We had completed our first set of exercises and were in pairs hanging onto the side of the tank ready to test out our breath-holding capabilities. When Tony’s turn came he ‘breathed-up’ as taught and then ducked under. The process was that the person checking the attempt (me) would tap the subject on the hand from time to time and the subject would respond by raising a finger; this was so that we knew they hadn’t blacked out. Fifteen seconds elapsed – tap from me and up went Tony’s finger; thirty seconds – tap, finger; forty-five – tap, finger; one minute – tap, finger. Thanks to the mammalian dive reflex, Tony exceeded his personal best by over a minute at his first attempt.
Put simply, life began in the sea and there’s a part of our bodies that has not forgotten this. The diving reflex is an evolutionary remnant which is triggered when our faces dip into water and it’s all about conserving oxygen. Nerve receptors in our face trigger a reduction in heart rate and blood vessels feeding extremities constrict, thus concentrating blood flow to vital organs.
While Tony was impressing everyone with his new-found static-apnoea skills (holding his breath and sticking his head underwater), I was coping with ‘slack-bladder’ syndrome. The water quality in the SETT was superb and I was far too polite to pee in the pool; thus, the process was – dive, get out, go to loo, pee, get back in, dive, get out, go to loo, pee, get back in, dive etc. After a while people started to notice and ask if I was ok. Although I made a joke of it at the time, I was actually experiencing a recognised side effect of the diving reflex.
With a bit of practice anyone can achieve the level of freediving prowess demonstrated by Tony (static apnoea) and me (slack-bladder syndrome). However, competition freediving is a whole different ballgame and one where the extent of the dive reflex is quite astonishing. This is all about pressure though which leads us onto Boyles Law.
Boyles Law
We need depth now; considerably more depth than we can access in the SETT.
Little Cayman’s Bloody Bay Wall is a vertical drop-off. The top of the reef is comfortably shallow at seven metres, but pop over the edge and there’s nothing to stop you until hit bottom at 300 metres.
In 2004, Glen and I spent a couple of weeks on Little Cayman; mainly soaking up the sun, ambling about on bicycles and sinking a few beers…etc…etc. It was my intention to do some scuba diving while we were there so as usual I presented myself to the local dive-master armed with log book accreditation, anticipating taking part in a few underwater expeditions. No chance! The conversation went something like…
“Hiya, any chance of a dive tomorrow?”.
“Uhgh – that’s really weird, your woman’s the image of (he mentioned some American ball-players name; famous at the time no doubt, but not to me, so for the point of the story we’ll call him ‘Babe Ruth’)’s wife; that’s just ssssoooo uncanny”. He stared long and hard (a bit too long and a bit too hard for my liking) at Glen. He took hold of my battered old blue logbook and shook his head.
“I need to see a ‘C’ card”.
“What’s one of them then?”. This bloke was starting to wind me up.
“Certification card; it’s plastic, looks like a credit card. This qualification’s no use you could have filled it out yourself and got anyone to sign it… are you certain that aint ‘The Babe’s’ wife?”.
At this point one of his assistant dive leaders weighed in on my side. “Gis-a-look (English bloke) … yeah, that’s ok mate, it’s a BSAC blue logbook and from the look of it this bloke’s been diving since God was a lad… let him dive”.
He responded to his assistant “Have you ever seen ‘The Babe’s’ wife? This broad’s the image of her”.
“Oh for xxxx’s sake!” (I’d had enough), “are you going to let me dive or not?”.
“Sorry, no, can’t take the risk, you’ll have to call England and get them to send you a ‘C’ card”.
I shrugged and Glen and I left the pair of them arguing. It was no big deal; the dive operation went to the same site, ‘Bloody Bay Wall’ every bloody day, which was handy as once I’d ingratiated myself with the dive team (luckily the man in charge didn’t bother to get involved in the diving), they kept an eye on me whilst I bobbed up and down among their scuba divers.
So that was the pattern. After breakfast Glen and I would cycle across the island, Glen would sit in the sun with a book and I’d snorkel out to where the dive boat was tied to a buoy (marine park, so anchoring not allowed). I’d stay on the surface, getting in the zone and await the divers big splash followed by a lot of whoooossshhh and bubblywubbly; commotion that was guaranteed to scare away a lot of the larger items of interest. Stationed away from the dive boat waiting on the surface, I could observe the exodus and was generally able to swim with turtles and side step the odd scary looking but harmless reef shark that sped by in a panic.
As the holiday progressed, so did my confidence. For safety, I made a point of staying in the vicinity of the dive boat and if I was intending to try something ambitious I’d do it within eyeshot of someone wearing an aqualung.
There is something truly magical about freediving Bloody Bay Wall; come with me…
Ok, so we’ve snorkelled across the reef and while the dive boat sorts itself out, we’re just resting on the surface looking down into blue merging into indigo. We’re lying with our heads facing to the northwest, with the sun on our backs. We can see the sunbeams like a halo surrounding us, with rippling shafts of light cutting down through the water, pointing out our path into the abyss. We breathe normally; we are relaxed; we are content.
We are aware of divers in the water now. As they complete their buddy checks, we fin back over to the top of the reef. We breathe with slightly more intent, but these breaths are only for preparatory dives. We glide down and swim with a turtle for a while; it seems neither afraid of us, nor that interested in us.
The divers have set off in a procession now. They have reached the edge of the reef and are following the sheer drop obliquely down, studying the reef as they go. Our aim is to track them from the surface, staying in front and waiting until they level out at thirty metres – the depth limit imposed by most holiday dive operations.
That’s it, they’ve slowed, they’ve reached their maximum depth. We continue to lie in their air-stream, exhaust bubbles bursting all around us. We move ahead of them again and make our final preparations for the dive. We close our eyes now and relax, then we start our ‘breathe-up’. One final concerted exhalation as we draw our knees up under us and force our diaphragms to eject as much air as we can. We pressurise our ears and take our final breath, packing in as much air as we can manage, and then in one smooth motion we flick our legs vertically out of the water so that their weight pushes us downwards. As soon as our fins are below the surface we take several strong fin-strokes, driving ourselves into negative buoyancy. We pass by the edge of the reef and continue into the abyss. We adopt a streamlined posture to ease our passage through the water. We orientate ourselves so that we are facing the reef; watching the teeming life will divert our attention from the urge to breathe.
As the depth increases we continue to pressurise our middle ears and sinuses, we breathe out through our noses just enough to stop our ultra-low-volume dive masks from squeezing onto our faces and damaging our eyes and their surrounding tissue.
We’ve stopped finning now, we are beyond the point of positive buoyancy and have started to accelerate effortlessly into the abyss.
We slow our decent by swinging our feet up and adopting a crossed leg position, holding the blades of our fins to ensure that we remain relaxed.
Our lungs were crushed some while ago and our stomachs have pushed up behind our diaphragms to help fill the void, leaving a pronounced hollowness between our ribs and our pubic bones.
We have drifted away from the reef now. As we look up we can see the divers above us. Time for us to think about the trip back to the surface, but before we do, take a look around and allow your senses to appreciate the majesty and the enormity of this environment. It is a dark grey world down here; most red light was filtered out by the time we reached ten metres and then, as we descended, the blue world turned to grey; look down and feel yourself drawn into empty blackness. For us this is a silent world now; we are too deep to be aware of the elemental interaction between sea and air. As we drift further down, away from the divers, the sound of their breathing fades to a whisper. We are virtually weightless, suspended in a shadowy void, with only the sense of increasing pressure telling us that we are drifting still deeper as a warm glow of intoxication envelops us… hold that thought!
A simplified version of Boyles Law tells us that the volume of an ‘ideal’ gas, in this case air, is inversely proportional to pressure. Basically, if you double the pressure you halve the volume. Air pressure at sea level is (sorry, this is getting boring) one atmosphere or fourteen point seven pounds per square inch. This pressure doubles at ten metres, which means that any air spaces in the body halve in volume, which is why divers need to equalise the pressure in their ears and sinuses as they descend to prevent eardrums from bursting, trickle air from their noses into their diving masks to prevent mask squeeze, and why anyone holding their breath as they descend experiences the air in their lungs seemingly disappearing. And, in my case, why thirty metres or so is about as deep as I can manage. By the time I get to thirty metres there is no air left in my lungs to trickle into anything!
For competition freediving though, it is a very different story, and in my view the stuff of nightmares. So, as we make our way back to the surface, the ‘nutters’ will be just getting into their stride.
Unassisted freedivers (constant weight) have exceeded one hundred metres. ‘No limits’ freedivers plummet into the abyss holding onto a heavy weight and, if still conscious, inflate a lifting device to get them back to the surface. The record for ‘no limits’ is in excess of two hundred metres. These athletes need to utilise different techniques to get air into their middle ears and sinuses and for the really extreme attempts, they flood these air cavities with water. Water is for practical purposes uncompressible, so ear clearing becomes unnecessary. And they swap diving mask for fluid goggles which are optically corrected and filled with water, thus negating the need for equalising the air space within a normal diving mask.
Back to the mammalian dive reflex. We’ve covered the basics due to immersion, viz. reduced heartrate and restricted blood-flow to our extremities. This served us well as we glided effortlessly down thirty metres or so into the Cayman Trench, but our competitive colleagues will need two other physiological aids – the ‘blood shift’ and the ‘spleen effect’.
Some while ago scientists calculated that fifty metres would be the maximum depth ever reached by a freediver. This was based on the assumption that compression of the chest would at depths greater than fifty metres cause it to collapse. As freedivers went deeper, it became clear that something else was going on. At one hundred metres, lung capacity reduces to roughly a tenth of surface capacity. Due to the mammalian diving reflex, as pressure increases, blood-shift occurs, diverting blood to the alveoli in the lungs. This engorgement replaces the space caused by the dramatically reduced volume of air. The spleen contains a lot of blood and as pressure increases still further, this blood is released into the circulatory system providing even more blood to replace the void left as the lungs shrink – uuurrrggghhh…. stuff of nightmares!
Remember my peeing problem? The technical term for this is ‘immersion diuresis’ and is caused in part by the diversion of blood to the chest cavity. This tricks the body into thinking that blood volume has increased overall and so it steps up the synthesis of urine. And there’s me thinking I was developing a slack bladder!
Anyway, we’ve enjoyed the sensation of freediving the Cayman Trench, now it’s time for us to head back to the surface and leave the serious freedivers to get on with it!
Henry’s Law and shallow water blackout (back to the Cayman trench)
Returning to our dive on ‘Bloody Bay Wall’. You will recall that we were holding our fins in a cross-legged fashion and enjoying the moment as we sank further into the abyss. The fact that we made it down this far means that we must have got the dive preparation right, therefore apart from the increasing pain in my ears and mask squeeze due to my inability to find any air in my lungs to compensate, we are still remarkably relaxed. Also, as we coasted most of the way down here, with very little finning, thanks to the diving reflex the blood getting to our brains is still well oxygenated. And, we are feeling pretty chipper, although not necessarily for the right reasons (see next section).
The problems begin once we commence the trip back.
We really are at my limit now, so let go of your fins, straighten up and start finning up towards the nearest diver; these are powerful strokes, we need to stop our decent and then get into a steady finning rhythm.
As we pass by the lead diver, we squeeze his arm and signal our ascent; we need him to keep an eye on us in case something goes wrong. Then we continue the trip up. As the pressure reduces the air in our lungs, face-mask, ears and sinuses expands again. We sniff the expanding air out of our masks (every little helps) and avoid looking for the surface as it is still a long way away. Until now, we have not felt much urge to breathe, but we do now and our pace quickens as the air in our lungs expands and increases our buoyancy. Ten metres and our finning slows five…four…three…two…one… breathe – breathe – breathe!
Henry’s Law (very roughly) states that the amount of gas dissolved in a volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. Basically, as depth increases the higher ‘partial’ pressure encourages the oxygen in our lungs to be absorbed into our bloodstreams, but as pressure reduces, the opposite occurs and oxygen is forced out of the bloodstream back into the lungs. Since pressure halves between ten metres and the surface, this is where the blackouts usually occur, and the problem is exacerbated by the fact that the urge to breathe is governed by the presence of carbon dioxide, not the absence of oxygen. Well trained freedivers have a very high carbon dioxide tolerance, therefore blackouts are common. The rules of competition freediving dictate that the diver should, on return to the surface, remain conscious, otherwise the dive doesn’t count. You have to wonder what the long-term effect of oxygen starvation has on mental capacity…
…now, where was I?
Oh yes, the impact of nitrogen on our mental capacity comes next… as if the lack of oxygen wasn’t enough to worry about!
Nitrogen Narcosis… and we’re still in the Cayman Trench
Before we started our ascent, we were glorifying in the unbelievable majesty of our surroundings; well just imagine for one moment that we were in fact on a serious attempt at a ‘constant weight’ freedive record, so we maintain our streamlined position and continue to accelerate past thirty metres with a self-satisfied feeling of wellbeing; as we glide beyond fifty metres, we know with absolute certainty that we are the coolest dudes on the planet; by one hundred metres we are invincible and convinced that nothing can possibly go wrong and if necessary we’ll hold our breath for as long as we like and if we can’t, what the hell, we’ll breathe the bloody water! Life is great, in fact life has never been so great… in fact we’re as pissed as farts! I think I may have over egged this description a bit, but hopefully you get my drift.
‘The narcs’ or ‘raptures of the deep’ as divers affectionately refer to them are yet another product of pressure. This time it’s nitrogen that’s the culprit. The increased partial pressure (Henry’s Law again) of nitrogen in the blood has a detrimental effect on nerve transmission in various areas of the brain, resulting in neurological changes similar to intoxication. Hence, nitrogen narcosis is also known as the ‘martini effect’. Evidently, from thirty metres down, each ten-metre increase in depth has the same effect as drinking one martini; not where I come from though matey, we Brit divers measure our narcs in yards of ale!
As with alcohol, if you ‘train’ hard enough you can increase your tolerance. Nevertheless, a ‘no limits’ freediver at two hundred metres could experience dramatic symptoms, which is no joke when you are trying to remember why you should pull the lever to initiate your return to the surface… uurrrggghhh… stuff of nightmares!
Seventy-nine percent of air is nitrogen, which, given its propensity for wreaking havoc with our brains is unfortunate. And then of course, we have to consider nitrogen’s other unpleasant side effect – decompression sickness, also known as ‘the bends’.
Decompression Sickness
Causes and effects of ‘the bends’ are fully understood by scuba divers. Freedivers are not generally at risk unless they undertake deep repeat dives. However, mix the two disciplines and the risks increase dramatically.
Back in the day, when scuba diving we used Royal Navy dive tables to calculate maximum bottom time, we moderated our ascent rate by watching our exhaust bubbles and making sure that they headed for the surface faster than we did, and, most importantly we stood by the mantra ‘plan the dive and dive the plan’. RN tables erred on the side of caution. Our continental cousins used Italian Navy tables; they spent more time underwater, did repeat dives and often got bent. Nowadays though, you strap a dive computer to your wrist, wear it for the duration of your holiday and allow it to do all your thinking for you – a bit like modern life I guess. Trouble is, you can still cock-it-up big time!
San Salvador Island in the Bahamas was our chosen location for ‘the usual’ and by now I had abandoned dive tables in favour of a computer. A dive computer senses depth, records dive duration and uses a paradigm to calculate nitrogen absorption and hence decompression requirements. I was well impressed with this gadget as it took all the brain-work out of scuba diving and allowed me to do repeat dives and multi-level ascents. In short, it was magic!
It was the end of our holiday and as I sat on the dive boat, just out from San Sal harbour, resting between dives, it didn’t occur to me that ‘gassing off’ (the rest period between repeat scuba dives) should be conducted out of the water, so in an effort to cool down, I grabbed mask, fins and snorkel and flopped over the side. Looking down into the water, I decided to fin down and have a look at a rocky outcrop; I had a fin around, flicked a couple of fin strokes and shot to the surface. I felt and heard a slight click in my neck, followed by the sort of pain you get with a seriously cricked neck, only much worse. Although I had an idea what had just happened, getting to a recompression chamber would have been problematic, so I kept it to myself, gave the second dive a miss, suffered agony the next day and then flew home. Although the pain eased, soft tissue in my neck had been irreparably damaged and as I aged, the symptoms recurred and eventually a neurosurgeon removed the damaged disc from my neck and replaced it with carbon fibre and titanium.
The rules are clear; don’t mix scuba and freediving. My mistake was to assume that because I’d dived safely within the parameters dictated by my computer, all was well. However, although the breath-hold dive down would have little impact on my overall dive time, the rapid ascent would have caused micro bubbles of nitrogen stored in the disc material to come out of suspension and froth, just like taking the top off of a fizzy drink. Hence the bend.
So, learn by my mistake… NEVER MIX SCUBA WITH FREE DIVING!
With that salutary warning, I’ll sign off. Hopefully, you have enjoyed the read – if so, I am pleased. If I have fired your imagination sufficiently for you to pack mask, fins and snorkel for your next holiday, then I am delighted. On the other hand, if reading this gives you nightmares, then my work here is done!
Just one more anecdote before I go though…
Footnote
You know when your mum said “don’t put your fingers in there – ITS HOT!” and you just couldn’t help yourself… story of my life!
There is a dive shop on Grand Cayman that is adjacent to the harbour in George Town. My recollection is one of friendly staff who when you ask “can I snorkel off of your back yard?” are very welcoming indeed. The site is noted for coral caves that are readily accessible from the beach and shallow enough (fifteen meters or so), to allow scuba divers plenty of bottom time without worrying about decompression. Glen and I were on our way home and I just fancied one last plunge and maybe a quick shufty at the entrance to one of the caves.
The first thing you notice as your ears submerge is the din from the cruise liners; a constant deep thrumming sound from big engines driving big propellers. Sound travels faster underwater than in air and the proximity of this noise is, to start with, quite unnerving. Nevertheless, once settled, it is a rewarding dive.
I snorkelled across the reef and was fascinated to see bubbles emanating from the coral; aha… divers in a cave maybe? I dived down to the source and sure enough, the bubbles were emerging from a fissure in the rocks. I surfaced and then finned twenty metres or so to the edge of the reef and dived down to the mouth of a cave, just as a couple of divers exited. I surfaced and swam back to the fissure in the rock; I poked my head into the fissure and the voice in my head said “don’t be a twat”, I listened to the voice and surfaced again, I rested, I ‘breathed-up’, and then I dived back to the fissure and decided that my shoulders would probably fit though – just. I listened for the voice again. Nothing.
I slithered through the fissure into a tunnel and sat down on the coral sand (this is where you came in). The dim glow from the cave mouth drew me towards it, but I’d only taken a couple of fin strokes when the cave entrance went dark. I was committed now; the fissure I’d entered through was thin and covered in weed, there was no way I was going back. As I approached the pair of scuba divers, one behind the other, blocking my exit, they looked surprised to see me. I clocked a spare demand valve hanging from the lead diver and relaxed somewhat as in the worst-case scenario I would be able to mug a few breaths. In the event, all three of us flashed the ‘ok’ signal; I flattened myself into the sand and the pair of them finned over the top of me. I popped out into the sunlight and back to the surface. There you go, after all that, no drama at all.
Time to ‘fess-up’ and give credit where credit is due
Sorry about the appalling cartoons. My original plan was to sketch out the cartoons and then get someone who can draw to do them properly. I considered approaching an ex Royal Academy of Arts Professor of Drawing, but after examining the standard of her work I concluded that my own efforts were more than good enough.
Tony Two took the photos of me freediving. Tony was wearing an aqualung at the time. The rest of the photos are my own and I too was wearing an aqualung at the time. Also, although the images were not necessarily taken at the locations described, the species depicted are consistent with those locations.
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