Rebreather NSS/CDS report from death at Peacock earlier this year.

[Rollin Bonz]

Having the appropriate spacer built into the bottom of the scrubber is the only solution I can see unless the use of multiple size scrubbers is eliminated.

I've only dived the Choptima with EA cartridges, so I'm not hands on familiar with any of these other units, but...

Maybe a floating base at the bottom of the scrubber housing (like an adapter that is permanently installed) that is spring tensioned that adjusts (compresses down) to match whatever sized scrubber is inserted? Seems too simple to have not been implemented, so there's probably obvious problems with that idea that, due to my lack of familiarity with these units and sorb use, I'm not considering.

 

[rjack321]

The Meg, SugGravity Defender, and XCCR all allow for different size (vertical length) scrubbers and corresponding spacers. I went to just using the standard 8# scrubber and appropriate spacer to avoid this potential operator error issue.

Please elaborate on how it’s possible to “design out” this kind of failure (operator error).

Make the spacer integral with the scrubber. All canisters are matched with only one scrubber using a key-lock system, flanges or integral tabs that only fit one way.

 

[rjack321]

Hammerhead gave out stickers to put in the canister to indicate proper scrubber height.

not ideal but a good first step

 

[ofg-1]

Thanks to the NSS-CDS for getting this report done.

 

[lostsheep]

Please elaborate on how it’s possible to “design out” this kind of failure (operator error).

Eliminate the spacer altogether by integrating datum features and a retaining mechanism to the side of the scrubber assembly that has to be in the same location.

 

[sunnyboy]

Since they sell multiple canister sizes with the same diameter, why not take the largest (longest) canister and put an internal plug in it to make the smaller volumes? THIS WOULD BE DONE AT THE FACTORY - so not something the diver does, but integrated and bonded at the factory so you still buy smaller 'volume' canisters but they are all the same physical length and so would always fit properly. The cost of a bit of extra material would be minimal given how much we spend on these units and the consumables.

 

[Alekseolsen]

Since they sell multiple canister sizes with the same diameter, why not take the largest (longest) canister and put an internal plug in it to make the smaller volumes? THIS WOULD BE DONE AT THE FACTORY - so not something the diver does, but integrated and bonded at the factory so you still buy smaller 'volume' canisters but they are all the same physical length and so would always fit properly. The cost of a bit of extra material would be minimal given how much we spend on these units and the consumables.

Fairly sure some USER have different scrubbers they use for different dives - Given the price of scrubber VS sorb I wouldn't bother (and this report is a very good reason not to do so!) but sime users would likely complain.

 

[211ratsbud]

A good way might be to identify the can and head combination(tiburon or classic) and have an internal shoulder(milled into the canister) the scrubber basket hangs from the top on using a flange. Allowing the top of the canister to be in the same place despite the length.

Alternative idea would be like JJ and couple the scrubber to the head.

 

[wgw04024]

This may be an ignorant question or overlooked detail in the report as not a CCR diver, but is there not any warnings when the loop becomes unbreathable from lack of o2? Also, are there any sensations a diver would feel that something like this is off causing them to jump to bailout out of caution?

 

[211ratsbud]

This may be an ignorant question or overlooked detail in the report as not a CCR diver, but is there not any warnings when the loop becomes unbreathable from lack of o2? Also, are there any sensations a diver would feel that something like this is off causing them to jump to bailout out of caution?

In these cases however the accumulated carbon dioxide is what presents the danger to the diver. Hypercapnia has a list of symptoms to which amount to an extremely dangerous scenario.

Including:
increased respiratory rate. Causing further CO2 build up.

The sensation of not being able to breathe and therefore the unwillingness to remove the tainted mouthpiece from ones mouth.

Further compounded by hyperventilating long after the tainted device is removed due to the lasting and lingering effects of hypercapnia and the amount of time it takes to bring pco2 below the physiological response threshold.

All of that hyperventilating is lowering the efficiency of which is effective gas exchange and contributing to a depletion of finite OC gas.

It's a really terrible feedback loop that warrants a lot of attention to detail in order to avoid on any CCR. As stated above perhaps an engineering solution could solve this one risk case of wrong scrubber to spacer condition.

Edited to add:

CO2 alarms have been attempted or applied in limited products, they usually cause more problems than they solve (my opinion from basic limited XCCR searching).

I think it's a case of the current technology is not adequate for the intended use case and since we are such a small industry we would likely have to wait for an outside industry to create something more suitable that can be repurposed.