UKRS Trip #97 - Chamber Dive at the National Diving Centre.  21st February 2004

A chamber dive?  As soon as it was announced I jumped at the chance, but then had to back out due to other commitments.  So it was with great delight when, with less than a week to go, Danny rang me back to say that he had got me on.

My deepest dives to date were 34m in Corfu and 31m in Stoney, I suffered a little narcosis on the Stoney Cove dive but that was more just a weird, uneasy feeling rather than full-blown "raptures of the deep".  I had no idea what to expect, I also had no idea how I would react or how my body would react, but to be honest I reckon that a recompression chamber is the right place to find out!

I turned up early, parked and was quite taken aback by the NDC.  It really is one *huge* hole in the country-side!  There is loads of parking space and a shuttle to take your kit to the water's edge many, many meters below.  But that wasn't why we were there, so having met with Danny and the rest we tested the catering van which provided us with steaming hot tea and coffee - their chip butties looked pretty good too!

We waited until the rest of the group arrived and until the last divers were out of the water, had a browse round the shop, filled out the disclaimers and waivers and waited for the briefing.

The dive was to happen in two groups, the first one of four people and the second of five.  The smaller group was to go first as the chamber was split into two parts, the main chamber and an air-lock.  The main chamber was pre-pressurised to 50m seawater and we in the first group would be "blown-down" in the airlock and then enter the main chamber for our bottom time, return to the air-lock and be "surfaced" in there.  The second group would be "blown-down" in the air-lock but the whole chamber would be surfaced as one.  This procedure saves a lot of time and air by not having to pressurise the entire chamber each time.

The chamber itself is a corker!  It was originally built as a "live-aboard" chamber for saturation divers and could operate at over 27Bar - that's 270m seawater!  It's original test pressure was in the region of 40-something bar!  The steel casing of the chamber is between 20 and 25mm thick with massively thick acrylic portholes and 100% ultrasound and x-ray checked welds.  Its original purpose would have seen three or more of these chambers bolted together as a place for up to 6 saturation divers to live for the duration of their duty - around 28 days!

Apparently, in this configuration they would have a toilet and a shower and not a lot else, meals would come in through a small air-lock to the main chamber.

So after the briefing it was shoes off and into the airlock and being last in was a little disconcerting, what looked like a reasonable space was more than a little cramped with us four and the attendant in there!  Getting the door shut was something else entirely and involved us all getting to know each other rather better!

The "descent" was interesting for a couple of reasons - first was the heat generated with the increase in pressure.  Suunto vyper's aren't the best at recording temperature so I can't say exactly what happened apart from that it got really quite warm!  The second thing was the difference in the feeling in my ears between the pot and water.  I found myself equalising three or four times per breath which seems like an awful lot.  I don't think the rate of descent was any quicker than I would do normally so it is either that I don't equalise enough normally or that it is just the difference in feeling between having water or air on the outside of the ear...

Once at depth, the door to the main chamber was opened and getting through it was the first test for narcosis.  Just working out whether to go through feet first or head first took some doing, the decision to go through feet first, when eventually taken, was probably the right one.  We got through into the main chamber and settled down to do some messing around.  The first thing that struck me was the difference in sound.  I'm no expert but I suspect that the increased density of the air in the pot means the speed of sound waves is altered resulting in everyone sounding a bit "cartoony".  By now the narcosis was having no effect whatsoever...

...until the attendant handed me a "breathing bib" which was connected through the chamber wall to a twinset of trimix.  Now I had two quick breaths off that and tried to talk to the other divers - most amusing!  Not having taken enough to relieve the narcosis, it was even more amusing!  The bib came back to me from Chris and this time I had a good long breathe from it and felt my head clear almost completely, then I handed it back to the attendant...

...the first breath of air made no real difference...

...the second I was feeling very warm and fuzzy...

...and with the third I was completely stoned again!

Which seemed like a good time to try the puzzle I'd taken with me.  I managed to start the stopwatch and take apart and put together a quite complex puzzle I've had for years in just under a minute.  I had no idea how long it would take me normally so I forgot about it and went back to existing.

After a while more we moved back through to the air-lock to begin our ascent, at this point I had no idea whatsoever how long we had been in the main chamber.  My computer was showing a dive time of ten minutes but I had no idea what that meant.  The start of the ascent had us all in stitches, on account of the fact that they have to start off pretty quickly to get the air-lock to main chamber door to seal - we had three Suunto computers in there and they all went mad at the same time from violating the maximum ascent rate.  The rest of the ascent was slower and very steady and we made decompression stops at 9m, 6m and 3m although all three computers "surfaced" as soon as we got to three meters (I have adjusted the profile in my dive log to reflect this).  Interesting things about the ascent were the reverse of the descent (surprisingly enough!), in that it got really quite cold.  There was a constant mist of condensation forming around us and when the balloon that the attendant had inflated at depth finally gave up the cloud that came from it was very impressive!

The whole experience seemed to go really, really quickly, feeling like only about 5 minutes but when we got out and I checked my computer and watch it was a good 25 minutes after I got into the pot!

I can only conclude that nitrogen narcosis' most dangerous effect is the time-warping factor.

I also concur with Chris and the others who all agree that this was a really good way of selling trimix courses....

The others readied themselves to go in while the air banks were refilled and took their places in the air-lock.  During their descent one of the group had an ear clearing problem and so the descent was delayed a couple of times until he got it to go - after 13m or so that was them fine until the bottom.  We looked in on them as they entered the pot and there was even more hilarity from them as they made their way into the main chamber.  This seemed to be the theme for their entire dive with people in continual hysterics! 

We had noticed that they had spent a considerable amount of time blowing up balloons and this was borne out by the somewhat "percussive" ascent!  They also had their stops doubled due to the altered descent schedule and were finally "surfaced" after 35 minutes.

I can only say that everyone enjoyed the experience immensely and I would recommend it to anyone, it is a fantastic way to become aware of just what nitrogen is capable of doing to your brain and of course to see why helium is your friend on deep dives.

So a quick pint of 6X at the Chepstow Hotel to warm up and then back to the car and the trek up the M4 and the back roads of Gloucestershire without heating, debating only for a split second whether staying home and fixing the heater matrix on the car wasn't a better idea...

...it still isn't fixed!

I seem to remember taking more than just two photos, but the negatives prove otherwise - they are here.

It only remains for me to thank Danny for organising this for us all and for getting me back on the trip at the last minute.