Info MIT Tech Review Article: Deep Diving on Hydrogen

[kimh]

…the dive was dangerous—not just to Harris who was risking his life, but for the people who supported him were risking a hit to their reputations and worried their friend may not return home. Harris and his team put it all on the line…

As fascinating/impressive as this was, I have to say- the way it was conducted seems a bit irresponsible to me. It’s admirable to be a pioneer and all, but I couldn’t help thinking about his spouse, too- not sure if he has kids. Diving to 750 feet on your first test is not exactly a methodical approach.

 

[arkstorm]

You may be interested in reading Ashley Stewart's article as well:

N=1: The Inside Story of the First-Ever Hydrogen CCR Dive

On Valentine’s Day, Dr. Richard Harris, aka ‘Dr. Harry,’ and the Wetmules made the first reported hydrogen (H2) rebreather dive to a depth of 230m/751 ft, in The Pearse Resurgence, New Zealand. The 13 hour dive, which was nearly two years in planning, was a field test to determine the efficacy...

indepthmag.com

If this doesn't inspire you to dream, to explore, to do something incredible, then nothing will.

 

[OTF]

As fascinating/impressive as it was, I have to say- the way this was conducted seems irresponsible to me. It’s laudable to be a pioneer and all, but I couldn’t help thinking about his spouse, too- not sure if he has kids. Doing your first test at 750 feet is not exactly a methodical approach.

H is not feasible to use shallower than that. It's an extreme option to enable extreme dives.

The reason is that H becomes a bit safer (less explosive) in gas mixes with less than ~4% O2. You can't dive such a mix shallow.

 

[kimh]

The reason is that H becomes a bit safer (less explosive) in gas mixes with less than ~4% O2. You can't dive such a mix shallow.

Good point. Do you know what the minimum depth is for 4% O2 to be practical?

 

[tursiops]

Good point. Do you know what the minimum depth is for 4% O2 to be practical?

Surely you can work that out. The calculation is part of any Trimix class.

 

[Brett Hatch]

Good point. Do you know what the minimum depth is for 4% O2 to be practical?

Deeper recreational depths -- my calculations suggest around 35 meters / 115 feet. I'll flag that I am not trained for hypoxic dives (or any tech dives for that matter), so take this with a grain of salt.

The InDepth article in the OP mentioned that they were careful to keep FO2 under 4%. I would be interested to hear how much wiggle room there is in this number, during a dive. If the FO2 reached 4.1%, or 5%, or 10%, what would happen? From what I'm reading here, if a H/O2 mix achieved some low threshold, ignition could occur instantly, without much of a spark at all:

The potential source of explosion that Harry was most concerned with was static ignition within the CCR itself, plus other potential ignition sources like electronics, the solenoid, and adiabatic heating. Industrial literature—or “sober reading” as Harris calls it—suggested that the tiny amount of static necessary to initiate a spark to ignite hydrogen is .017 mJ, 400 times less than the smallest static spark you can feel with your fingertips and several hundred times less than required to ignite gasoline. “It ain’t much, in other words,” Harris said, noting that counterlung fabric rubbing against itself could generate just such a spark.

Yikes. If anyone with greater scientific knowledge than I could comment on the likelihood of a sufficient spark for catastrophic failure as the FO2 exceeds 5%, I would be grateful.

 

[kimh]

Surely you can work that out. The calculation is part of any Trimix class.

The idea was to elicit a response.

 

[inquis]

Good point. Do you know what the minimum depth is for 4% O2 to be practical?

Harris apparently felt a PO2 of 0.7 to be practical (lower would presumably be too much deco or not enough cushion against O2 delivery issues). If you've had a nitrox class, you would have learned the fundamental equation:

PO2 = FO2 * Ambient Pressure​

From that, practical depths would be deeper than 165 m / 550 ft.

 

[kimh]

From that, practical depths would be deeper than 165 m / 550 ft.

I thought I remembered him doing the H2 switch higher than that (0.7?). But even for 550 ft … 750 ft is another 200 ft descent (!) That’s a very significant difference, even if you don’t consider physiological or gear issues that might scale faster than linear. In unknown territory like this, who knows what inflection points might be there? And in 6° water in a cave (wasn’t he solo for the deep segment?) Not exactly what I’d call conservative.

 

[inquis]

wasn’t he solo for the deep segment?

No. He switched to hydrogen diluent at 200 m and both dropped to 230 m. "A comfortable depth" in his words.

Not exactly what I’d call conservative.

Most was not new. He's been in 6 deg water before and well prepared. He's dived that dual rebreather many times. He'd even been to that very spot before (on helium, like his buddy). It took nearly 2 years to get all the ducks in a row for this dive.

I'm pretty sure he was as conservative as he felt was necessary. People with his experience are in a completely different class, to put it mildly.