CO2 Sensor

[iain/hsm]

How long until a CO2 sensor is incorporated into a rebreather design? a year, 5 years, or a decade?

Not a bad guess, they were first made available in 2004 so six years now. LOL.
Contrary to public opinion and comments that you may have read on web sites. The first C02 detector for rebreathers have been available for a number of years. First shown at the DEMA 2004 show and again at DEMA 2005.

The perceived lack of availability has IMHO been twofold, first a marked reluctance from the recreational scuba rebreather manufacturers to add C02 detection to there products due to the additional cost, but also that most had only an interest to copy.

Also coupled with the position that originally prior to the DEMA 2004/5 it was a military rebreather controller and this was seen as being too competitive, so in 2004/5 it was shown with an option of a purely passive detector of C02. This then had limited interest, as its original ability to fully control the UBA with pp02, ppC02, depth, time, etc etc put it in direct competition with the then available sports rebreather controllers that manufacturers already had and the C02 controller was trying to sell to in the first place. A catch 22.

Also in Europe we have the CE directive EN 14143: 2003, regarding rebreathers basically its a law regarding rebreather design and sales. In the original 2003 document it states “C02 detector (If Fitted)” In the latest 2009/10, document edition it also still states the same "if fitted" bull****.

The “If Fitted” part pretty much kills any hope of selling a separate detector in Europe for sports rebreathers as it was effectively kicked out by the CE rebreather manufacturers who are also members of that committee. I understand one now has there own inferior version using a commercially available low cost “vegetable green house” detector and fudging the inaccuracy of the reading by only offering the display as LED’s not numerical. They also from their website claim to be (another) “First in the World” LOL.

At the same time the US Navy also were also interested in C02 detection but at the time digital canister temperature mapping was the big thing with NEDU. Interestingly a similar idea to a method used in Europe prior to C02 monitoring as a indicator of the canisters reaction progressive heat wave. One of NEDU leading exponents of canister temperature mapping also eventually “won” a patent on that process so life support system design got the “Temp Stick”.

C02 Detector vs Temp Stick. 1st test results in - Rebreather World

From a 2005 post shows I think the first time C02 detection was seriously discussed on RBW back in 2005 and shows a photo (somewhere) of the 2003 prototype controller “Brick” on a LARV oxygen set if you can be bothered to read all six million pages of the thread. LOL

The latest controllers are also used in small Transportable Two Man Recompression Chambers to data log and graph out both the chambers depth, TTUP time and temp with both the 02 and C02 in the chamber as well as a patient/diver/tender profile data recorder.

I still have the original graphs and divers test results on file from the August 2004 DEMA flier, as only some were published on that old RBW post if anyone is interested.
The latest versions of the C02 detector and UBA controllers are non mag STANAG A certified for MCM military use to 200MSW and are in field use. Iain Middlebrook

 

[spacemanspiff1974]

Without trying to be rude, I would think that hypercapnia would be less of a risk than hypoxia or oxtox. One simple way to avoid would be to choose a scrubber design that prevented channeling such as the radial design of an ouroboros, or a meg radial. The sentinel and o2ptima can also use extend air cartridges from what I recall. Another choice would be to follow the guidelines for scrubber duration.

Sentinels are certainly available and not rare some would seem to suggest. I've tried one out before and Delta P is an established company.

Hey Frank, I hear rumors that the spree is running a second tech trip on the oriskany in september for those of us who are not hypoxic trimix. Is this correct?

 

[wedivebc]

Without trying to be rude, I would think that hypercapnia would be less of a risk than hypoxia or oxtox. One simple way to avoid would be to choose a scrubber design that prevented channeling such as the radial design of an ouroboros, or a meg radial. The sentinel and o2ptima can also use extend air cartridges from what I recall. Another choice would be to follow the guidelines for scrubber duration.

Sentinels are certainly available and not rare some would seem to suggest. I've tried one out before and Delta P is an established company.

Hey Frank, I hear rumors that the spree is running a second tech trip on the oriskany in september for those of us who are not hypoxic trimix. Is this correct?

Hypercapnia is a serious threat in any rebreather and the scrubber is only part of the equation. Mushroom valve failure, expired absorbent, internal bypass due to mechanical failure or incorrect assembly of the unit are just some of the ways hypercapnia can kill. It would be wrong to say just use a radial or EAC to minimize the risk because it just ain't so. However I still think we are a long way away from a reliable system for monitoring CO2 effectively no matter what some RB manufacturers are claiming.

 

[spacemanspiff1974]

Hypercapnia is a serious threat in any rebreather and the scrubber is only part of the equation. Mushroom valve failure, expired absorbent, internal bypass due to mechanical failure or incorrect assembly of the unit are just some of the ways hypercapnia can kill. It would be wrong to say just use a radial or EAC to minimize the risk because it just ain't so. However I still think we are a long way away from a reliable system for monitoring CO2 effectively no matter what some RB manufacturers are claiming.

I agree with you that hypercapnia is a serious threat. I was thinking of channeling issues and not changing sorb. I would also agree with you that other mechanical issues may result in hypercapnia. Perhaps I should say that I worry more about oxtox or hypoxia from my admittedly limited exposure to rebreather diving.