The complexity is ensuring the rebreather bailout will be reliable, not switching to it. Imagine keeping your rebreather ready to dive in a diving bell with two of your dive buddies.
The bell is dripping with salt water from hot water suits and humidity, divers bang into everything in such confined quarters, and nothing is handled gently. How confident would you be that your absorbent will be dry under these conditions and after being locked out on a working dive for 4 hours?
Sure, you can lock the unit out between dives so surface technicians can pre-dive the rebreathers, but that increases turn-around time when swapping divers between shifts. This matters a lot when the DSV (Diving Support Vessel) costs hundreds of thousands of dollars/day and the operation depending on divers completing a task often runs into the millions of dollars/day.
This is done all the time. If you do a bit of digging on their website and online you’ll see the company who makes them has a track record with another rebreather bailout system called SLS which has been used on many bell runs and dives all over the world for a number of years.
"Still warm" lasts about 15 seconds when hot water is lost. Hot water suits are very loose-fitting, have no insulation, and respiratory heat loss on HeO2 is hard to imagine until you have experienced it. Shirt-sleeve comfortable in a chamber at 200M/660' is in the 32° C/90° F range. Thermal conductivity of Helium (98.5% Helium, 1.5% Oxygen @200M) requires heating the breathing gas, also with hot water. Ambient water temperatures at working depths in the North Sea are typically in the +/- 3°C/38°F ballpark.
A diver's umbilical was severed several years ago in the North Sea and it took 45 minutes to recover him. Amazingly, they started pouring hot water on him when the diver was returned to the bell's trunk (tubular extension below the hatch) and he recovered in a few minutes. Reports indicate his open-circuit bailout was not empty. It appears that his body shut down from the very rapid cooling when hot water was lost, before he could burn up the few minutes in his bailout.
I hope this helps put my comments into perspective.
If the diver has enough time to go OC he has enough time to engage this unit. It’s a single twist at the sideblock; same as OC. Company has put a video online and you can see the diver activate the system.
https://www.youtube.com/watch?v=P5Gi-eSwQzU&list=PLushsE3JnCvo4nv_dqU8e5rcOhI7etrEM&index=2
This is from a real dive in the North Sea. Although I’ve never used a hot water suit, I’ve dived in the North Sea hundreds of times (with a drysuit of course) so I do have some feel for the conditions. I’m 100% certain that it would take more than 15secs to go from comfortable to completely incapacitated if the HW supply was lost. In fact, the incident you refer to corroborates this. It involved a diver named Chris Lemons. Details are in this article (and elsewhere online):
https://www.offshore-technology.com/features/featurelifeline-lost-documenting-a-divers-near-death-dramatic-rescue-in-the-north-sea-4809349/
I’ve seen the film, Lifeline, referred to in the article while sitting in a room with some of those from Bibby who made it. The diver, despite losing his HW supply when his umbilical parted, remained conscious and mobile for quite some time and managed to climb up a substantial subsea structure. If he had been incapacitated by cold within 15secs this would not have been possible.
I also recall that he did actually exhaust his bailout supply. You’ll also see in the article that he wasn’t out of gas for 45mins, it was up to 26mins. When the question was asked “how did he survive?” the answer was “WE DON’T KNOW”. The article says a subject matter expert thought it could be the high po2 he was breathing that saved him after the CO2 knocked him out plus the extreme cold shut down non-essential parts of the body. The cold shutdown didn’t happen in seconds though. I’m not sure then that it can be said it was definitely hypothermia that saved him when even the experts and those involved can’t say that. It was however probably a contributory factor. I don't think he had hot water poured over him either, at least not before he had already regained consciousness, as the rescue diver and bellman basically thought they were recovering a dead diver.
I’d also point out that this was a one-off incident and there are fatalities where the cold didn’t save the diver. They simply ran out of gas. I’d suggest therefore that it’s not a good SOP to rely on hypothermia to save a diver when his umbilical is severed/trapped rather than ensure he has as much gas as possible. To take the view that there’s no point in having up to 45mins of gas as you’d be shut-down due to cold before it was used is startling. You might shut-down but you’ll still be breathing shallow (if there’s gas) and stand a chance of rescue. Besides, not all incidents are in the cold North Sea. When an emergency happens would you rather have <10mins of gas or 45 mins of gas??
Lastly, the incident you mention in support of there being no point having lots of gas involved diving from a vessel called Bibby Topaz. Ref the excerpt attached from recent publication from the rebreather company about where some of the new units have been used…
Bibby Topaz in the
North Sea at +110m.
Not just worn, but activated and actually used in various tests to determine that the diver can return safely to the bell. Again you can see it in the video. Would they have bothered if they thought more gas was a waste of time? This also demonstrates to some extent that the kit is up to the rough and tumble of sat diving (as you’d expect from a company that makes sat diving equipment). In the excerpt above the company says it worked closely with Bibby in the R&D and testing so I would expect it’s up to the job. Would these people have decided to use the new rebreather if there was an issue with robustness after the incident you refer to?
And finally, before anyone asks, I have no axe to grind here. I just think it’s unhelpful when someone who clearly has a lot of knowledge and experience (and therefore respect from the diving community) decides to dismiss a new safety innovation in a public arena without actually knowing much about it. Given your status and credibility, some people will be inclined to accept your argument no questions asked, however your status brings with it a certain responsibility. Please exercise it more considerately and take the trouble to find out the facts before casting judgement.
I’ve no intention of getting into a game of internet forum ping pong on this one so I’ve said my piece and I’ll leave it there. I certainly don’t doubt your credentials, but I think there are one or two aspects of your posts that needed to be countered.
PB
