Chamber dives - how safe are they?

[Mikael]

The club did one several years back (before I joined) and one of the guys who did the dry dive returned later in the day as a precaution because he was concerned he might be exhibiting some signs of DCI. We can not be sure if it was DCI and the guy from what I hear had been busy the day before doing some hard labour so it may have muscle fatigue simple due to that or at the other end of the scale a contributing factor to a real case of DCI, we just don't know. I have never had a chance to meet the guy, so I only know what I have been told by a third person who was present at the time.

This has been up for debate in our club recently because us younguns are interested in doing it. The third person who told the story would do it again but was keen to emphasis the risks involved. I would have assumed that the risks for DCI are lower on a pot dive even to 50m compared to a 30m wet dive because ascent is controlled (presumably well within the tables), you are more comfortable, warm and not in the dark.

Also some of our members went on a technical visit to the National Hyperbaric Chamber in Aberdeen a few weeks ago. One of them then emailed NHC asking if they organise dry dives with an interest in experiencing and learning about the effects of being narked. We got the following response;

'I'm glad you enjoyed the visit and it gave you something to think about.
Please advise your diving club that we do not want to see them, ever, unless it is under planned visit circumstances...
As to the dry-dive, it is not something that we offer and unfortunately need to decline your request. It involves an element of risk which we are keen to avoid and the best advice to your club is to recognise that narcosis will happen and to plan accordingly, or ideally avoid it.
If you wish to have a visit at some point to see the NHC than we could arrange depending upon dates, activities here and numbers.'

That's fair enough, I really hope I'll never ended up in Aberdeen unless it is under planned circumstances
Joking aside it gives no info on the element of risk and it is this I am keen to learn more about. Can any one point me in the direction of incident reports or data on the number of incidents of DCI due to chamber dives?

[j07cmt]

PFO's? Undeserved hits?

[Richard_severn]

Im sure you will have seen this page but it may be worth dropping them a email and asking if they have any incident reports etc they may send you them.

hth

[jamesp]

I`ve done two pot dives with dive clubs I have been a member of.
One to 50m, one to 40m.

On the 50m dive, we were a large group and were divided into two "loads".

There was then a third trip for I think 4 people who were displaying signs of skin bends!

So it can happen.

[Mikael]

PFO's? Undeserved hits?

'Undeserved hits', what's one of these when its at home? There maybe unfortunate hits, say you got tangled in line and dragged to the surface. Irrespective of whether your diving was potentially dangerous or unsafe I don't think any one deserves a hit.

As for PFO's I guess these are not something we normally account for and everybody who dives is accepting (though most probably never think about it after the initial lecture) that there is a risk involved that you may have a PFO. If you are not willing to theoretically do a 50m wet dive then I guess you should not do a 50m dry dive either.

[Hickdive]

Exposure to pressure is a risk. We choose to do it underwater voluntarily and we control our own ascents therefore we have only ourselves to blame if we get bent. If we do get bent then the risk of treatment is outweighed by the risk of non-treatment.

For a 'recreational' dry dive in a chamber we are voluntarily exposing ourselves to a risk but allowing someone else to control our ascent, theoretically leaving them liable.

You might think that it would be churlish and stupid to sue a pot if you got bent after a fun dry dive. However, the MOD doesn't recompress civvies any more after someone sued, alleging his residual symptoms from a bend were the result of his recompression rather than the original dive. So churlish and stupid people will lash out with litigation if someone else could possibly be blamed. Clearly Aberdeen have decided to avoid that risk.

[gobfish1]

when i was a BSAC member we had a few outing for a pot ride 50m ,, we used to have a v nice time ,, pot ride
then 3hr in the pub that was just over the road ,, we had to hang round for 3hr ,, on the off chance someone needed a 2nd ride ,, we never had no problems ,,

id say its about as safe as doing a 30m dive ,, id not worry about it ,, 99.995 your going to be fine ,, BUT ,, LOL

Preston Police ran/owned the chamber , i went to ,, and thay were v good ,, it was a long time back tho,

[j07cmt]

I'd say an undeserved hit would be one where the diver has done nothing wrong, and dived within the tables, and is generally fit. Some kind of medical anomaly maybe

[Mikael]

I quite like the idea that the NHC are more interested in treating divers then organising fun dives, its oddly reassuring even if the the risk of litigation might be real reason. This is all speculation though.

What is interesting is that there is a certain commercial element that comes into play. For example Midland's charge £40 per head for a 50m dive and decompress you on 100% O2.
I wonder how much bottom time and how much deco time is given. Is there commercial incentive to reduce deco time to a the minimum 'safe' amount so their staff and chamber aren't tied up to long?

I have always understood that the risk of going on dry fun dive is to be offset by gaining first hand experience of what being narked under controlled conditions and that this may help you recognise it when wet diving. It concerns me that I have never consciously felt narked when at depth despite rationally knowing that I should be even to some small degree. How narked can I get before I notice or worse still can I keep getting narked and never realise?

[Mikael]

I'd say an undeserved hit would be one where the diver has done nothing wrong, and dived within the tables, and is generally fit. Some kind of medical anomaly maybe

Ok I see what you mean. That said there doesn't have to be a medical anomaly, the tables are only guides and every diver is different in how their body reacts to compressed gases, so padding out a safety or deco stop is not bad idea. Thankfully I dive shallowish (by YD standards) where hopefully things are more forgiving.