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Date:
Thursday 27th October 2011
Venue: London Diving Chamber
Participants: Denis, Daniel, Steve, Teresa and Richard
Dive Time: 49 Minutes
Max Depth: 50.3 Metres
Average Depth: 17 Metres
| Profile
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We
all pitched up around 1800 for the dry dive at 1830 with the exception of Richard and Teresa who showed their customary disregard
for time by turning up at 1820. After they hurriedly changed into hospital scrubs (the required dress for the
evening) - watched by the bemused smiles of their companions - our guides for the dive, Bill and Emma talked us through what
was to happen.
| Our Sunday Best
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Bill told us that Hyperbaric treatment, and especially treatment on high partial pressures of O2, Hyperbaric Oxygen Treatment
(HBOT) has been effective for sports injuries due to raised O2 blood plasma levels oxygenating muscle tissue.
It's also now being used for treatment after radio therapy to help healing healthy tissues damaged by the therapy.
After the briefing, we were given a small test to complete.
We had to circle all instances of the letter 'l' in a piece of random text.
The chamber (AKA 'pot' or 'rocket') is in two parts separated by an inner 2 inch thick steel door.
It has an outer and inner compartment. The outer chamber also has two inch thick steel outside door.
The outer compartment acts as an air lock for those wishing to enter the inner compartment whist it is still pressurised.
We were ushered into the inner chamber by Emma, and the two 2 inch thick steel doors were then closed behind us.
| From the Outside Looking Out
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Our dive computers were shoved into a bucket of water and were all told
to relax, some of us succeeding better than others. Pressurisation commenced after we put on ear defenders (to
protect our ears from the noise from the compressors and the noise of ingress of air).
We were told to equalise frequently, and we all seemed to need to do this far more frequently than on
an ordinary dive - perhaps up to once every five seconds. Should any of us have had problems equalising, the dive
might have been stopped, so we were all eager not to let this happen.
When we reached 'bottom' at 6 bar, 50 meters, the compressors were cut and we were able to talk to each other about
what we were experiencing. The most obvious change being in our voices which all sound high pitched and somewhat
like Bugs Bunny. It was amusing to hear Denis' cultivated and measured baritone reduced to a Scottish squeak!
Richard and Teresa both reported feeling quite anxious, and Richard said he felt the influence of narcosis quite strongly.
Whilst our tests showed an all round impairment in mental performance, only Richard claimed to have felt any real difference
in thought processes. He said it suddenly switched in at around 45 meters and was not as he expected.
It was not like drinking alcohol according to him but it did definitely impair clear thinking. The much talked about
euphoria was absent. Richard reported that he hadn't noticed the exact instance that his anxiety and thought impairment
had gone, but it seemed to be gone completely by 35 metres.
Denis
writes: 'Where there was the, not unusual, mildly stilted atmosphere talking with the chamber staff prior to the
dive, as we descended there was some relaxation and better interaction with Emma and much more general chitchat. There was
a definite sensation of mental fuzziness somewhere around 30+ metres and carrying out the exercise at 50 metres required much
more concentration than at the surface, along with some physical clumsiness; my handwriting was even worse than usual'.
Teresa and Steve both reported that they had pains in their backs or neck.
Steve identified his as occurring oat the site of a previous injury that he hadn’t felt for some years. Emma agreed
that these might be the results of old injuries. Equally, they might have been due to anxiety and/or narcosis.
Emma handed out test sheets again, and we did the same test again circling
the letter 'l' on another piece of random text.
Our
tests complete, and after a little more chatting and questioning by Emma, we slowly decompressed and were thus on our way
back to the 'surface'. Unlike the descent which was hot and stuffy because the air was compressed and losing
heat, our trip to the surface was decidedly chilly and very misty, demonstrating, to Denis' relief, that the laws of physics
were still intact!
At 14 meters, 2.4 bar, we were given pure oxygen
from masks tightly strapped to our heads. A ppO2 of 2.4 bar fortunately didn't cause the facial twitches, or bodily
rigours, or any other hideous symptoms of CNS poisoning that we've be trained to expect at such high O2 concentrations.
It merely helped us to flush the excess nitrogen from our tissues, minimising any possible risk we had of DCI. We continued
to breathe pure O2 until we surfaced.
There as a brief rest
at about 4 metres whilst Bill flushed the air in the chamber, apparently because the O2 levels in the chamber had gone up
to 23% and the CO2 levels had risen, too (even though there was a CO2 scrubber in the chamber). Emma was not wearing
an O2 mask, so this flush was done for her, and because high levels of O2 are a fire risk.
Back at the surface at 1 bar, the doors opened, we changed back into our day clothes, and Bill collated
our test scores.
Our Test Results ordered by percentage decrease
in performance
Name
| Surface
| Bottom
| Percentage Decrease
| Steve
|
22
| 22
| 0
|
Richard
| 18
| 16
| 11.1
| Denis
| 23
| 20
| 13.0
| Teresa
| 28
| 22
| 21.4
| Daniel
| 17
| 13
| 23.5
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At 50 meters Daniel had felt that the test was very easy and had been
confident that he had done better that at the surface. The results, he points out, showed that in fact he had suffered the
worst fall in performance of the whole group. The effect of depth had been a significant degree of overconfidence as well
as a marked drop in actual performance.
And we were all surprised
that we'd had 12 minutes bottom time. It seemed very much shorter to all of us - five or six minutes at most, perhaps.
Denis identified that he'd had a similar experience of time dilation when diving to 35+ metres and experience of others
having this issue at 40 metres plus.
Bill talked us through some
of the more technical details of the chamber for a little while, then it was off to the pub for a lengthy decompression...
| Plumbing
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| Inside
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| From The Inside Looking Out
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