Help Needed Designing Carbon Dioxide Scrubber

de.jones

Hi,
I acknowledge this isn't your usual diving rebreather sort of question but i figured your experience would probably be valuable!

I am a student at Durham University looking into the spatial variability of carbon dioxide within caves. To do this it is important that any echaled CO2 is removed.

Is there any product currently on the market that could be easily adapted or recommendations of methods of scrubbing that would be suitable for such a purpose?

Thanks for your time

David Pye

I'm not quite sure I understand your question.

You say you're after something to remove exhaled CO2 - are you after something to remove exhaled CO2 from an air pocket in a cave, or a rebreather scrubber for divers investigating the cave?

David

Edit: Or are you after an overland 'rebreather'?

de.jones

Sorry i should have made myself clearer!

Breath CO2 needs to be removed as it is exhaled so as not to unduly concentrate the gas whilst a measurement is being taken.

I think "overland rebreather" covers it!

David Pye

Ah, gotcha.

Well, there are two easy options I can think of:

1: Get a diving rebreather, ditch the counterlungs, cylinders etc. You want to be left with just the scrubber, mouthpiece and hoses. Disconnect (and probably remove) the inhalation hose, but leave the exhale hose connected to the scrubber canister. That way, on inspiration you'll suck air in through the inhalation hose and exhale out through the scrubber canister (which will then vent to air).

2. Get a mine rescue rebreather (smaller lighter scrubber usually) and remove the inhale side of it, as well as the O2 cylinder etc.

Other options:

Build one You have the advantage here in that a scrubber 'breakthrough' will be annoying as it will throw off your measurements but it wont be disasterous in terms of hypercapnia at 40m!

So, you could either have a container you inhale *AND* exhale through (higher work of breathing but you can have a smaller shorter duration scrubber to manage this) or have something slightly more complicated with a pair of flapper valves meaning you would only need to exhale through the scrubber.

You could run some tests to find out how long your scrubber lasts by measuring how long it takes for measurable CO2 to come out the far end, and then set whatever 'safety margin' you like

johnv

look for a mine rescue rebreather, these come up on ebay fairly frequently.

Biomarine make them, (amongst others)

Or just make a simple "non" rebreather without a counterlung, and inhale & exhale through a lime canister, you won't even need an open / close mouthpiece. This is fine provided you are certain the O2 level in the cave will sustain life.

Also, if you are working in an environment that won't support life, ensure you have a backup of some sort.

have fun
John

tibby

If it were me and could afford it I would wear a fully closed O2 rebreather while inside the cave area to be measured and not worry about using or contaminating the cave environment at all.
It's pretty simple to make one especially if it doesn't need to be submerged. I'm sure you can find a lot of instructions on the internet on how to make one. The most expensive part is the oxygen bottle and the button to inject it. You can adapt a paint respirator mask from Home Depot to make it easier to breathe (through nose). For a counterlung you can use a hydration bladder from an outdoors store (3-5 liters in volume) and you can buy corrugated hoses from a dive store (replacement BCD inflator hose such as Dive Rite).
Make sure to carry enough oxygen for the duration (~1-4 liters per minute depending on workload). Also the scrubber needs to be of decent size, maybe holding 2-3kg, to last several hours.
Do not attempt to dive with it though (unless you really know what you're doing of course).
There are other, more experienced people on this board that can help with this design I'm sure.
Or you can buy a mine rescue rebreather off ebay as suggested above and use it as is.
Just be aware of dangers like CO2 poisoning if the scrubber fails or there's some kind of bypass. There's also a danger of the oxygen catching on fire if not handled properly.
If you don't understand the principles and working mechanism yet try to do so before attempting this.

Tibby

__________________
Does the voice of reason change when you add helium to the mix?...hmm

WD8CDH

I would go with either a full closed circuit O2 rebreather or a scrubber that you only exhale thru. A scrubber that you inhale thru will remove come CO2 from the atmosphere that you are trying to measure. That may or may not be a problem depending on the size of the space and how much air flow there is in the cave.

__________________
Ron Schroeder
Former Commercial Diver, now Lazy Diver

Sutty

Actually if there is significant CO2 in the atmosphere then an exhale-through-only scrubber will remove some CO2 from the atmosphere too - the CO2 you inhale and then exhale again. I doubt this would be significant unless a small space and/or the observer is there for an extended period. Of course if significant inhaled CO2 you might well want to breathe from an independant source anyway!

If you have a CO2 monitor you could constantly check that the output of the scrubber contains no CO2, thus confirming that exhaled gas has not contaminated the environment being measured.

__________________
Never forget that life is a finite resource.

de.jones

Thanks for all the responses.

A closed circuit rebreather system would be ideal scientifically, but practically given financial constraints and the fact that it would likely be hefty (therefore not really suited to caving) I think an exhale-through-only scrubber will be the likely solution, however many of the absorbants i've looked at seem to max out after a couple of hours, which will likely not give enough time.

David Pye

Hmm.

You'll either end up with a *huge* scrubber canister, or you could have several smaller ones to swap between.