Going for a dry-dive!
Ever fancy diving to 50m without getting wet?
Aren’t they all supposed to be? Well, yes, if you’re in a dry suit (and even then I’ve seen some fairly wet dry-suited divers due to some mysterious leak). In this case we’re talking about a dive in a hyperbaric chamber, rather than in-water.
At 18:30 on Wednesday 3rd August, 8 of us from the club (Chris Hunka ﾐ organiser, his son James, Howard Hope, Andy Ethel, John Fowles, Steve Collard, Christine and Clive Corner, plus myself) met to undertake a 50m dive at the London Diving Chamber, which is located at the Hospital of St John and St Elizabeth in St Johns Wood. Wednesday is a good day, as by then they’re likely to have completed treatments of anyone who has undergone hyperbaric treatment as a result of an incident at the weekend, but dry dives are always subject to cancellation if emergency patients need treatment!
We were all unsure as to what this was going to entail, except for Steve Collard who has previous experience of hyperbaric chambers (this, I should point out, is from a previous job working in the North Sea oil industry).
The hospital is conveniently located a short walk from St John’s Wood tube station and we met up outside so we could be directed as a group to the hyperbaric facility. The chamber itself is housed in it’s own building in the grounds of the hospital and is attended by dedicated chamber attendants, who have both nursing and diver qualifications (this chamber advertises itself as run by divers ! for divers).
We started by having to show our diving qualifications, giving the date of our last dive and completing a routine medical questionnaire, with questions very similar to the standard self certification declaration. Next we parted with ｣25 quid each, this being the fee for the dive (so, competitively priced for one dive)! Then we were all issued with medical ﾒscrub suitsﾓ (or smocks and trousers) to change into, which came in 2 standard sizes: too big and too small, but thankfully with waist ties and easy to roll up arms and legs. The reason you donned these became apparent once we were being compressed (read on!). Then we went into the adjacent room which housed the chamber.
Here we met David Sharman, the chamber supervisor who was to undertake the dive with us, plus a second attendant who operated the external chamber controls. As you can see from the picture, the chamber itself is a huge horizontally mounted cylindrical structure, with a bench running along either side which just about accommodated the eight of us. We entered via a pressurised door, went through an ﾒante-chamberﾓ (effectively an air lock) and through another pressurised door into the main chamber. The reason for this is that it provides two independently pressurised areas within the chamber giving the ability for someone to enter or leave the main chamber whilst under pressure, into the ante-chamber (which is then brought back to atmospheric pressure so they can exit, or taken down to the same pressure as in the main chamber to enter).
Once seated, we received a safety briefing from David Sharman. Although there was no water, we were still going to experience the same effects of changing pressure as if we were descending or ascending during a ﾒnormalﾓ (in-water) dive, so we had to be able to clear our ears to equalise. Also, although roomy and with several small observation ports on the side, the chamber does sometimes cause a claustrophobic feeling, especially as the air inside also gets quite misty (like a fog) on ascent. All the time we were breathing air at ambient pressure (oxygen is provided through masks to breathe at intervals if you are actually being treated). Cameras (even depth rated underwater cameras) were not allowed in the chamber ﾐ for a combination of safety reasons, but also liability if they were to break.
Briefing over, the two pressure doors were sealed and we started our descent. Having been forewarned, we also took in a few items to see the effects going down to 6.0 bar pressure would have on them. These included a standard neoprene hood, several dive computers, some balloons ﾐ either part blown up at the surface, or when at pressure, an aero chocolate bar (remember the advert, they’re so light as they’re full of bubbles) and some jaffa cakes (the latter as supplies in case anyone got hungry during the dive ﾐ not something you can do underwater – or was Chris just telling fibs about them).
We donned ear defenders (as air being de-pressurised quickly is ﾒnoisyﾓ ﾐ as we all know if we open our own cylinder valves) and descended slowly to 6m, then 10m, ensuring everyone could equalise. Howard had a problem with his ears, just to show it really does happen with pressure change and not only underwater. Then slowly on down to 50m, all the time being watched by the chamber supervisor, which is why David was in there with us. Now, the reason for the scrubs. Think about what happens to your own cylinder when filled with high pressure air ﾐ it gets very hot. Imagine being inside that cylinder, you can feel the air noticeably coming in around you in the chamber and you also feel the growing heat as the pressure increases (and sweat ﾐ yuk)!
We stayed down at 50m for a few minutes, long enough for Chris to surprise us with a diving-related test he had cunningly devised (on the surface, when lucid), although I’m not sure why we had one question about naming four places that began with the letter ﾒYﾓ, or come to think of it why the question about the Training Officer (TO) had the answer pre-completed for you !.. perhaps it was because our TO had written the test himself?
There were several very noticeable effects about being pressurised:
- Our voices went really squeaky, not quite like when you inhale from a helium-filled balloon (this should not be tried at home), but rather think of ﾒthe only gay in the villageﾓ from the TV series Little Britain, crossed with Donald Duck and you get the idea.
- The neoprene hood was ultra compressed, lost most of it’s sponginess and was much thinner than at atmospheric pressure.
- The aero bar was fine (well, hot and sticky like the rest of us) although on ascent a number of the bubbles under the chocolate coating did pop and expose the minty green below (yummm). Oh yes, and the jaffa cakes were unaffected and tasted the same at 50m as on the surface (yes, they were supplies after all).
- The pressure did affect our reasoning abilities, just like we’re warned happens with nitrogen narcosis (or this is a good excuse for doing badly in the TO’s test and getting simple questions incorrect)?
- A couple of the dive computers left in the air consistently read 3m different to those put in a bucket of water (so once we re-surfaced still showed they were down at 3m ﾐ are those Suunto’s reliable now Chris)?
- Balloons really do shrink under pressure and expand when de-pressurised, and if you do blow them up when under pressure they will burst as the air inside expands and keeps doing so until they go pop.
Tests completed and marked, we then started our ascent, being slowly re-pressurised as we were brought back to the surface. This time the air was much colder and a mist formed in the chamber, although we did dry off. We carried out the equivalent of a number of short stops, starting from 18m (as I recollect) and then a safety stop at 6m, in much the same manner as if we had actually dived underwater to a maximum depth of 50m for a few minutes’ bottom time.
And then the dive was over and we were back to atmospheric pressure once more, having logged a dive to 51.1m for 50 minutes. Those who had remembered them got log books stamped, Andy Ethel snapped a few group piccies outside the chamber and we changed out of our ill-fitting scrubs. We all agreed it was very good to experience, albeit not the same as actually being 50m underwater and having the sensation of ascent and descent (as in the chamber we stayed seated on the benches all the time). But it was an excellent way to demonstrate and see the effects of pressure ﾐ on the spongy neoprene hood, the squeezed and burst balloons and the effect that breathing air at depth has on your reasoning.
Remember, emergency hyperbaric treatment is provided free at LDC, under the NHS. They also provide information on DCI and medical advice, offer DCI, Diver Medic and chamber operation courses, plus provide diver medicals. Details can be found at www.londondivingchamber.co.uk.
So next time someone asks, ever fancy diving to 50m without getting wet, you’ll know what they’re talking about! Thanks to Chris Hunka for organising a very unusual experience!