Ever wondered what it would be like to do a DRY DIVE? Dempster Marples North London Scuba dry dive at Whipps Cross Hospital, Hyperbaric Unit Would you be nervous to be enclosed inside a hyperbaric chamber to be pressured up to 5 atmospheres and enjoy the strange effects of such an unusual and vivid experience? I must have been, because during the previous night I had a weird dream about being at a hyperbaric chamber and not being able to find my green prisoner-clothing that I knew we would have to wear to make the trip. An anxiety dream if ever... This dry dive was a good way to learn about the effects of pressure on the body and mind, in the safe environment of a hospital. Without the added strangeness of diving in water we could concentrate solely on the effects of pressure on us, rather than worrying about where our dive buddies were, where our compass was pointing, where our exit point was or how much air and nitrogen time we had left. The physics and other boring important stuff was handled by the guy outside the chamber who was driving the strange ship. The chamber is used to treat divers with the bends, but also to assist treatment of a number of other medical conditions including MS, gangrene, treatment of trauma to the skin... etc. The effect of oxygen in air under pressure speeds up healing and can even increase the effectiveness of antibiotics A bunch of us had turned up, some looking suitably nervous... others playing it cool (but also nervous)... all of us looking forward to whatever the immediate few hours held in store. In my experience us scuba divers are a funny bunch of hedonistic macho types, who snigger in the face of death and never ever... ever... admit to making a mistake, or God forbid fessing-up to it openly afterwards for the ridicule of our peers. Some of us however were nervous about clearing our ears (like when you descend in an aeroplane). My feelings about this were that if I am diving I can regulate my own descent, but on this trip someone else was going to be driving. With this in mind, Wayne and the other staff from the centre kindly relaxed us in the pre-brief with a mixture of physics, biology, medical info and good humoured camaraderie, which took minds away from the serious procedure that we were about to experience. We dressed in our green fatigues, and were allowed to keep our knickers and socks, but the rules were no acrylics (cotton only), no grease (lipstick) or make-up, hairspray or anything else that could prove flammable. Anything that could be taken off should have been, though we were allowed to take our dive computers inside the chamber, to be placed in a bucket to activate them, to record our depth, and also our cameras, though they had to be inside 40 metre rated waterproof housings, to prevent damage and fire risk. At 5 atmospheres (5 atm) pressure, everything becomes flammable, so static electricity, or electrical components are to be avoided at all costs. The air inside the chamber was to be with the usual 21% oxygen. This oxygen level was not to be allowed to stray to even 23% at which point the slightest fire would have been uncontrollable, probably even for the amazingly efficient water spray system designed to dampen any such emergency by filling the chamber with a heavy vapour of mist which would have rendered visibility impossible, even from one side of the chamber to the other. The chamber was quite a big cylinder, and sitting inside was a bit like sitting in a small tube carriage on the underground. I felt no claustrophobia of confinement and the presence of the others and Wayne of the hyperbaric unit was enough to keep our minds occupied and calm. The seats were like aeroplane seats and I almost felt strange not to be buckling up... clunk click. We had been split into two groups, with six of us (including myself) in the first group. The pre-flight prep included wiring up the masks which would feed us the pure oxygen that we would be breathing for the last part of the procedure to help our systems off-load all the excess nitrogen that our bodies were to absorb during the dive. By flooding our blood with oxygen we would drive out all the nitrogen in our system and vastly reduce the time that we would need to spend in decompression to avoid getting the dreaded bends. Bends is caused by rising too quickly in the water (de-pressurising too quickly), which causes nitrogen bubbles to form in our saturated blood in the manner of champagne when the cork pops. Oxygen makes me nervous. Though qualifying as a Nitrox diver early in my diving career, (its not a career, its a hobby for me) I did not use it much until fairly recently as bad bad things happen to divers, who overload on oxygen. If you overload with nitrogen, medicine can usually get you out of the soup. But there may well be no way back for the diver who overloads on oxygen. There are (may be) symptoms (PADI divers may recognise the acronym VENTID which lists them), but unconsciousness and convulsions are rapid, sometimes without warning, and underwater quite probably fatal. However the pre-lecture made it very clear that this procedure was going to be the safest dive we had ever made or would ever make, as the physics was very conservative. In any event overloading on oxygen is not an easy thing to achieve if you know the rules and stick to recreational diving limits. Now that Ive got my brain around this fact, I am more relaxed when breathing Nitrox (enriched air) under water. However, as we all know every procedure, and every dive carries a tiny risk. For example, 1 in every 30,000 dives in cold water results in decompression illness (DCI). The stats are better for warm water at 1 in 80k. But if we worried too much about this level of risk we would certainly never get inside a motor car. After familiarising ourselves with the chamber and hearing what to expect, the doors were shut and the countdown communicated to us via the outside phone... one minute to take-off. We were given cups of water and boiled sweets to suck. I decided to video rather than take still photos throughout with my camera. When it started, the pressure on the ears was immediate and more vigorous than when diving in water. We had been told to stick our hands up and ask to stop asap, if we were in any kind of distress, especially with our ears. The suddenness and immediacy of the pressure increase left me swallowing the water from my glass hard, and much relieved that my ears were just about coping. I was not surprised when one of us needed to halt the descent twice in the early stages to give their poor ears and sinuses a chance to catch up with equalising. At the first stop I was amazed that we had only reached 4 metres. It seemed much more pressure than at the bottom of the pool at Edmonton. Everyone was holding their noses and blowing, but I found it easier to continually swallow and my right ear was clearing slightly quicker and easier than my left. After a few moments we set off down again. A further 4 metres down (8 metres depth) we needed to stop again to allow our colleagues ears to catch-up. This time the stop lasted for nearly a full two minutes. I have often noticed in water that clearance is most difficult in the first few metres, but after 10 metres or so becomes much easier. After our second stop this also proved to be the case in the chamber as we were able to steadily descend without fuss to our target depth of 40 metres. By 15 metres the chamber was beginning to warm up very considerably from its initial temperature. When we went in the air was probably around 18°C, but by this time we were all sweating at around 25°C, as the temperature rose to 33°C at the bottom. This is described in the physics text books by Charless law. Wayne was standing, while we were all sitting so he was getting the worst of the heat at the top of the chamber, and there were beads of sweat on his brow. There was a strange and very distinct thermocline in the chamber itself as it misted up slightly. It was hot at the top, and my face was flushed with the heat, but my feet were still cold, and you could feel the distinctive difference if you put your hands down next to your feet. By 18 metres, Waynes banter was starting to turn all Mickey Mouse with the increasing density of the air. Equalising was much easier now with a steady rhythm established as we descended down into Advanced Open Water territory below 18 metres. I was starting to notice the usual sluggishness of thought which meant that nitrogen narcosis was on its way. Narcosis slows my brain as if Ive been at work for 12 hours. Creative thought is difficult. I also feel a little dreamy. It is often compared to being drunk, but I think it is more like being tired. Our friends in the second group were waving in to us from time to time at the two small port-hole windows in the side and door of the chamber. Past 25 metres I noticed that the narcotic effect was affecting everyone as we were visibly relaxing, smiling and laughing. Anxiety for most of us had turned to enjoyment by 30 metres as we headed down into Deep Diver specialty territory. By this time we sounded like extras from a Warner Brothers cartoon with squeaky voices . A beach ball that had been full at the surface was crushed to the point where it looked pretty empty of air and a yellow balloon was noticeably smaller. Quite alarming if you think about it. When I go this deep I always have a feeling that my body is taking a pounding and that I am taking liberties. I am always tired at the end of a deep-dive day. Wayne held his Cressi computer to my lens showing 35 to 36 metres of depth, and 11 then 10 minutes of no decompression time left. At 40 metres we were doing a lot of laughing but I felt curiously on edge, as it was almost dream-like with the warmth and sluggish thought processes. I breathed in hard and was initially quite alarmed that the air seemed almost like treacle going into my lungs. For a few fleeting moments, I wondered if I was getting enough air and felt slightly anxious, but I told myself that this was similar to breathing through a regulator, with the feelings of slight restriction with which I am familiar at depth. Having logiced this out in my mind I was fine, though never quite relaxed in my addled condition. One of us had done some juggling with some brick toys at the surface and amazed me by still doing it faultlessly at 40 metres. Very impressive indeed. Wayne had shown us a little wooden stick on the surface which was attached to a small plastic parachute. On the surface I had counted three on release before it touched the floor. At 40 metres I counted 7 before it touched down. Next he gave us all a ruler test, (drop a ruler and see how far it fell before we managed to catch it) and I was quite impressed that I managed to catch it before it got more than half way down. One of us missed it altogether and it hit the floor! Wayne took delivery of something through the small chamber-box in which it is possible to feed things in from the outside world. The chamber is opened from the outside, and then, when the door closed it is possible to pressure it up to the pressure inside the main chamber, after which you can retrieve whatever has been delivered into the chamber. We were all doing the written psychometric tests at this point, and I am amused at the answers that I gave to most of the 7 questions on the paper. I got my name correct (which was the first question). I managed to do a maths sum involving addition and subtraction. I correctly identified the number of atmospheres at a specific depth. Without giving too much away my other answers were hilarious. I drew a shape with one too few sides. I did a simple multiplication wrong. I joined some dots, missing two of them by a good centimetre! And we had to remember a six digit number which we had been given on the surface (which to be fair to me I couldnt even remember before going into the chamber), but in my narcotic state I had even forgotten to try to remember the number in the first place. No way I could guess it down at 40 metres. I enjoyed the sluggish way in which those opposite me relatively slowly pushed shaped wooden bricks through the holes in a young childs toy. One of the quotes of the day: Theres no triangle... (Oh yes there was!) We handed round a small bottle of cola to shake as much as we liked. The pressure inside the chamber meant that when it was opened it did not fizz at all. All the gas was held in solution despite all the vigorous shaking. The next trick involved a half empty plastic bottle of water. The top was put on it at this depth with the plan of opening it at the surface to see what happened. Waynes computer was calibrated perfectly at 40.0 metres. We waved our hands about and could feel the density of the air at this depth. We were given a 1 minute warning and after exactly 10 minutes at 40 metres, we commenced our steady 5 minute ascent back to 9 metres. By wiggling our jaws we easily cleared on the way back. At 35 metres Waynes computer indicated that he needed to do a 3 metre 2 minute stop. It was immediately colder in the chamber as the decrease in pressure brought the temperature crashing back down in double-quick time to something that really felt quite cold very quickly. blankets were passed through into the chamber from outside through the little chamber mentioned above. At 33 metres there was a distinctive mist in the upper part of the chamber indicating a thermocline as we continued to rise. My ears were popping of their own volition all the while, as Wayne with the wisdom of experience put on a cotton pullover that he had brought with him into the chamber, while the water vapour swirled all around the chamber throughout the ascent. At 9 metres we commenced our safety stop and reached for our masks to breathe the pure oxygen that was going to flush the nitrogen from our saturated blood. Waynes computer showed 9.4 metres and required a 1 minute stop at 3 metres, indicating that he could get to the surface in 2 minutes if necessary. But this was based on breathing air, while we were all on pure oxygen. Hence there seemed no way according to theory that we could get DCI. After two minutes at 9 metres we ascended during the next minute to 6 metres, where we spent a further 11 minutes degassing on the pure oxygen. We had been told not to talk when breathing the oxygen, so the de-gassing was as boring as it sometimes is in the water. All our dive computers were sitting in a bucket of water, and one of them started to bleep an alarm, as it thought that the dive was being made purely on air. In the final ascent from 6 metres I watched the still slightly deflated beach ball magically re-inflate as we headed back to the surface. After the main door to the chamber had opened Wayne opened the half full bottle of water. At 40 metres the still-water had absorbed some of the air into solution, in the same way that the blood of a diver with the bends reabsorbs the nitrogen bubbles in the chamber under treatment. The top blew off with a spectacular pop as the 5 atmospheres blew it off like a rocket. The bottle was instantly filled with steamy vapour as the air in solution migrated from the liquid almost instantly. We exited the chamber and changed back into our clothes while the second group got ready to take their turn. I filmed some of the descent from the porthole window and watched the beach ball collapse again. I watched part of the second groups ascent through the port-hole window, with the familiar misting up at the start of the process, and then the masking up at 9 metres for their de-gassing on oxygen. After everyone was out of the chamber and ready, we went back into the classroom for a long session which concentrated on the importance of reporting any anomalies to the hyperbaric centre, if you have been diving. One thing that sticks in my mind was an old black and white film which showed what happened to two mice that were given pure oxygen under pressure. One of them went into convulsions and was bouncing all over the place. When it came to, it was completely disoriented and reacted aggressively towards the other mouse, which had somehow avoided passing out. One lesson from this was that two individuals react differently under identical circumstances and would react differently again on a different occasion. So dive conservatively. We dwelt at length on the different factors contributing to DCI which exist and are not accounted for in the mathematical models and dive tables. Age, smoking, hydration levels, temperature, fatigue... all of which impact and can multiply to give a diver with a perfect dive profile the bends. Nearly all the diver who come in for treatment have perfect dive profiles. These other factors and perhaps yet more factors that we could call just bad-luck all played their part to DCI. We also discussed the vital importance of specialist insurance outside the UK. So DIVE CONSERVATIVELY. We listened for over an hour to Waynes de-brief and safety information, which was necessary to ensure that everyone was physically OK (no bends) after the hyperbaric chamber. I had really enjoyed this unique experience. The centre staff were fun, down to earth approachable and friendly. The overwhelming message was not to be shy to phone the Hyperbaric centre after diving for advice if you feel that anything is unusual. An early phone call can reassure or lead to early treatment, which is always easier than leaving it until later. The event is really useful for any diver. When I enrolled to include the PADI speciality, I suspected that I was just collecting scout badges, but I now think that the information, knowledge and practical experience passed on in this invaluable training morning, should be made compulsory for anyone who wishes to complete the PADI Master qualification. The reason that I have changed my opinion is that this was so clearly about safety and solid advice, that it is invaluable as a reminder of knowledge learned on the Open Water, Deep and Rescue courses. This serves to reinforce the safety message and clearly will help me to be a safer diver. It gives the practical experience of a chamber, which takes away some of the perceived horrors and gives of taste of how the treatment would work should you ever need it. Do this course if you ever get the chance.
Posted on: Thu, 22 Jan 2015 07:00:59 +0000
Trending Topics
Recently Viewed Topics
© 2015