HSE Video CO2 Rebreather incident

[MattS]

Just had this link passed on to me.

HSE Video CO2 Rebreather incident (http://www.hse.gov.uk/diving/video/co2video.htm?ebul=hsegen/26-nov-2007&cr=8)

I wonder how many other CCR divers will go "phew!" when they hear the cause of the problem?

[Kev Roberts]

What a fantastic clip.

It is frightening though to think what could have happened.
Was this a genuine mistake by the training organisation or was it a cost cutting exercise?

Also should the saftey diver have stepped in and recomended aborting the dive?

[Mike Rowley]

What a fantastic clip.

It is frightening though to think what could have happened.
Was this a genuine mistake by the training organisation or was it a cost cutting exercise?

Also should the saftey diver have stepped in and recomended aborting the dive?

The impression anyone would get from this CD and the fuss the HSE have made is that this was a common occurance. This is not the case, I have not heard of any other instance of any instructor teaching nonsense such as this and as far as I am aware no agency advocates this practice. Indeed all instructors I have come across stress not to do this. If this was any more than an isolated case we would be seeing many CO2 hits in the incident statistics and that is not the case.

When BSAC Technical Chief Examiner, I had to send a circular to all BSAC rebreather instructors advising them that this practice was dangerous and not to be taught, despite the fact that our manuals are very clear on how to pack a scrubber. This to satisfy one particular HSE inspector. Initially this HSE inspector tried to claim the instructor was a BSAC instructor and was quite aggressive in his approach. We were able to show that the incident happened at least a year before BSAC launched its ccr course therfore it could not possibly have been one of ours. It was quite clear at the time that he did not know who the instructor was, it should have been easy to trace. If he had evidence that an instructor was teaching this nonsense he should have taken action against the instructor, the school and the agency, I am not aware of any such action having been instigated.

IMHO this is a classic case of poacher turned gamekeeper. Trying to suggest that this practice is endemic is more a case of one particular HSE man trying to raise his own profile and using an isolated incident as the vehicle.

Mike

[John Bantin]

http://www.divernet.com/cgi-bin/articles.pl?id=1093&sc=1006&ac=d&an=1093:Kit+Q+&+A+July+2005...

[deveugle]

I might be the only to have picked up on this, but was anyone else surprised by the panicked breathing rate being quoted as "most likely around 160-200 l/min" ?

Is this something that is substantiated (and if so can anyone provide references) ? On the one hand I could see this being some dramatic licence, on the other hand , with the amount of CO2 build-up that is possible with a rebreather, ths might just be possible with a completely freaked out diver breathing increasing concentrations of CO2. Even though it seems enormously high as compared to the, in my mind, normally quoted "panicking" 50 l/min. Seems this would have rather huge consequences on bail-out, both on OC and CC. (You would suck a 10 liter at 200 bar empty at the surface in 10 minutes or so - seems unlikely even when panicking).

By the way is there any more "capacity" for CO2 retention on a rebreather as compared to OC ? Although the source of CO2 would be harder to "produce" on OC, I would imagine (pure speculation) that, given the same amount of CO2 quantity available (contaminated source on OC versus defective scrubber on CC), there is a lot less potential for CO2 to linger around in an OC tank/breathing system, where it gets flushed out, than in a closed circuit system, where CO2 keeps getting added (and where the available volume in the hoses etc is bigger). This higher amount might then make a differerence in "panicking" breathing rate ?
Something along the lines of:
- CO2 triggers breathing therefore, more CO2 triggers more breathing cycles (i.e. higher breathing rate)
- More CO2 on CC than on OC means higher emergency breathing rates on CC than on OC

This might explain the quoted 160-200 l/min (for CC but not on OC) or might be pure fantasy on my part.

Anyone with insights?

Peter

[Gareth]

My understanding is that when the Navy did stress testing on Navy divers, they found that breathing rates escallated to over 100l/min initially & remained very high until the 'first point of safety' was reached.

The first point of safety is very subjective, dependent on the individual. However this was normally either the first deep stop or the first gas switch (individual dependent)!

I hope Mike R's along shortly, he has more definitive figures than my rather unreliable memory!

Gareth

[Nigel Hewitt]

I might be the only to have picked up on this, but was anyone else surprised by the panicked breathing rate being quoted as "most likely around 160-200 l/min" ?I sat down one day and did a test with Apeks TX50 regs and breathed as much as I could for 60 seconds on a 3L tank measured with my digital blending gauge and managed 100L/min.

I am reasonably convinced that the restrictions were my throat and lungs.
I did it on the floor and that was good as at the end my head was spinning.
Nothing could have got me higher so multiply 100L/min by depth in bar and that's what I max out at.
- CO2 triggers breathing therefore, more CO2 triggers more breathing cycles (i.e. higher breathing rate)
- More CO2 on CC than on OC means higher emergency breathing rates on CC than on OC
I've done a CO2 hit and it wasn't the quantity that was a problem but the fact that some brain stem instinct kicked in and said "You are not allowed to stop breathing. Even to swap onto that nice reg in your hand."

All the while my brain was screaming "It's CO2! Breathe the d**m bailout!"

Thankfully the brain was still working so I switched to exhaling through my nose and let the ADV feed me clean gas. I can't tell you how many breaths it was but a pause became negotiable and I switched. Cleared my flooded mask (virtually blown off) and discovered my son had hold of my jacket and I was about to be CBLed.

[Mike Rowley]

My understanding is that when the Navy did stress testing on Navy divers, they found that breathing rates escallated to over 100l/min initially & remained very high until the 'first point of safety' was reached.

The first point of safety is very subjective, dependent on the individual. However this was normally either the first deep stop or the first gas switch (individual dependent)!

I hope Mike R's along shortly, he has more definitive figures than my rather unreliable memory!

Gareth

The RMV figures we were quoted were between 50 and 80 l/min with a possibility of up to 100 l/min. These were actual RMVs recorded during incidents. These relatively high RMV figures were recorded as lasting until the first point of perceived safety was reached and then subsiding gradually to normal thereafter. There was no mention of 160 - 200 l/min, however, the former figures were based on bailout scenarios but not necessarily CO2 hits. My view is that the 160 - 200 l/min are hyped figures, in keeping with the hype of this CD. I would need to see some evidence before accepting such a high figure.

I too, like Nigel have experienced a CO2 hit. Two significant facts concentrate the mind. Firstly stats tell us that few people experiencing a CO2hit actually baleout. Some say the reason for this is fear (apparently special forces use high PCO2 to induce fear for training) others say it is due to denial. My view is that it probably begins with denial at the early stage and progresses to irrational fear. Secondly, removing oneself from the source of CO2 does not alleviate the symptoms, it only prevents them becoming worse. The symptoms of CO2 toxicity last for hours, in my case from about 1400hrs until midnight, I went to sleep with them and woke up ok the following morning. These two facts combine to make CO2 hits particularly dangerous. At the moment there are no sensors available for rebreathers that are affordable and will sense the very small PCO2 that is toxic (> 5ppm).

Whilst CO2 toxicity is a hazzard to be aware of for rebreather divers it can also happen to OC divers. I witnessed a particularly bad OC CO2 hit a few years ago when a diver had to be rescued from 50m by his buddy. He blacked out at least 3 times on the ascent and was semi-conscious and cyanosed at the surface. The cause we identified as a poorly set up regulator that had recently been serviced. He didn't swap to his secondary reg.

Mike

[John Bantin]

Ask Peter Readey about the time I had a CO2 hit! (I discovered a design defect in the scrubber canister of an early PRISM that has since been rectified.) I was still in the boat but managed to hit the water and descend to a few metres before I fought my way back to the surface. Rapid breathing? I nearly had a heart attack in the process.
It took hours to recover. I don't believe anyone would be able to bail-out to OC under these circumstances. Your brain does not work because you are too busy trying to exhale the poisonous gas.