Report on first deep hydrogen dive using a rebreather

[Dr Simon Mitchell]

Hello,

This subject has come up in a few threads elsewhere, but the 'official' (peer reviewed) report on the hydrogen dive performed by Richard Harris in the Pearse Resurgence last year was published yesterday in Diving and Hyperbaric Medicine Journal. I have attached the paper here.

Harris RJ, Challen CJ, Mitchell SJ. The first deep rebreather dive using hydrogen; case report. Diving Hyperb Med. 2024;54(1):69-72. doi: 10.28920/dhm54.1.69-72. PMID: 38507913.

Simon M

 

[Big-swede]

First of, a big thank you to you and all the people involved for pushing boundaries and exploring new ways forward.

A couple of questions:

Is there any "follow up research/testing" planned, for example testing where you measure when/how HPNS happens and how much hydrogen is needed to prevent this?

Are you developing a less "hands on" way to perform the gas switch to hydrogen and somehow monitor the percentage of the different gasses live?

Best regards Felix

 

[sea_ledford]

Thanks for sharing that Simon! I have a question on the method of introducing hydrogen to the loop. Why was the decision made to blow the gas into the loop rather than have a premix that was switched to at depth and do a full dil flush? I know the volume of gas would have been significant at 200M, but was the variability of the potential bottom mix just not that big of a concern?

 

[Mobulai]

Thanks Dr Simon for sharing, been sitting on fire and twiddling thumbs waiting for this.
Big thanks also to the teams of scientists and divers, and especially to “Hydrogen Harry” for pushing boundaries, look forward to reading it within the next few days.

 

[Dr Simon Mitchell]

Is there any "follow up research/testing" planned, for example testing where you measure when/how HPNS happens and how much hydrogen is needed to prevent this?

Are you developing a less "hands on" way to perform the gas switch to hydrogen and somehow monitor the percentage of the different gasses live?

Best regards Felix

Hi Felix,

I think it would be a little grandiose for me to claim that there is some sort of 'test program' planned. I suspect that this will progress in small incremental / anecdotal steps and it will never really be something validated by numbers / data other than accumulated experience. The problem is that even doing one HPNS-producing technical dive below 200m is a big deal in terms of planning / logistics / cost etc etc (especially in places like the Pearse Resurgence - 6 degree water temp, habitats needed, no road access). There are some plans for further dives this year, which are hopefully conducted safely, and these will add to the experience.

There are various approaches to introducing hydrogen to the loop and one suggestion, raised by sea_ledford below, would (at least to some extent) make the process a little more precise. I suppose if you had a helium analyser in the unit a titration of pure hydrogen could be more accurate.

Thanks for sharing that Simon! I have a question on the method of introducing hydrogen to the loop. Why was the decision made to blow the gas into the loop rather than have a premix that was switched to at depth and do a full dil flush? I know the volume of gas would have been significant at 200M, but was the variability of the potential bottom mix just not that big of a concern?

Yes, this issue was discussed and debated etc. The overarching consideration was that this was our first exposure to hydrogen, and to our knowledge no others had been undertaken on a wet bounce dive to such deep depths (the COMEX work was mainly around saturation exposures). There were various predictions / concerns about things like some sort of 'cold shock' when suddenly changing to hydrogen at depth in very cold water. Harry did have a bailout rebreather with no hydrogen to jump to if necessary, but nevertheless, on this first occasion he wanted the addition to be very titratable so he could introduce some, breathe it, assess the effect, then introduce more in a stepwise way up to a level roughly calculated to produce the target fraction of hydrogen in the mix. We were not too concerned about precision. The most important consequence of overdoing it would have been narcosis - again with the idea of titrating up hopefully avoiding that. With all that said, having this first experience behind us I suspect your idea will get some serious consideration for subsequent dives.

Simon M