Dry cave bad air

[jason]

Must give credit to Jason Gulley...we went into a dry cave in the Ocala area and it was a bit lacking in O2 and he used this method to evaluate the breathability ...the flame would barely go and needless to say I was a bit short of breath on exit....

I'd forgotten about that trip!

The lighter test is a quick method of getting a rough idea of whether or not air might be safe to breathe. The lighter test actually reflects the concentration of O2 in the atmosphere. While O2 is converted to CO2 by microbial processes in the subsurface, the final relationship between CO2 and O2 in air is not 1-1, as described in this series of experiments conducted by Australian cavers (http://nhvss.org.au/wp-content/publi...0Helictite.pdf). While the lighter test is better than nothing, and many, many cavers have used it extensively to guide safer exploration of caves with high CO2, the only reliable method of knowing the actual concentration of CO2 in the atmosphere is to buy a CO2 meter.

While CO2 meters used for scientific work can be pretty pricey, if you're only interested in figuring out if you should be breathing the air in a confined space, meters are pretty reasonable ~$100 (http://www.co2meter.com/collections/...table-co-meter). You can transport these in a tube through sumps and then open them up when you arrive on the other side. At $100 each, its not the end of the world if they get flooded....

Finally, I should point out that it is a common misconception that CO2 gas in caves comes from decaying vegetation in caves or from CO2 degassing from dripwater. There is a group of cave researchers (including me) that have been studying the origin of cave air CO2 for several years now - the isotopic signatures of CO2 in cave air (and other lines of evidence) indicate the most likely origins are (A) decay of dissolved organic matter in the space between the soil zone and the water table and (b) respiration of tree roots. The CO2 diffuses through fractures and pores in the rock and accumulates in areas of the cave that are poorly ventilated, such as low spots. Much of our current research is on understanding how the production of this CO2 is linked to formation of caves in places like Florida, Guam, the Yucatan and the Bahamas (or any other location where the limestone is highly porous, which includes parts of the Domincan Republic). In other locations where the rock is less porous (Kentucky, Tennessee, Missouri, etc.) the production of CO2 between the soil and water table exerts an important control on climate records preserved in speleothems.

In the case of air bells between sumps, high CO2 concentrations are sometimes possible due to degassing of CO2 dissolved in the stream - particularly if the stream originates on the surface and sinks into the ground.

My recommendation would be that anyone diving sumps in tropical environments should consider buying a CO2 meter.

[victorzamora]

The biggest problem would be calibrating the O2 analyzer. Normally, you calibrate it right before making a measurement.

It shouldn't be hard at all, right?? You know what you've got in your tank....you can calibrate based off of your tank contents (obviously known) and then proceed. I know some analyzers are locked in to the mode of "zeroing" to Air, but the Oxycheq unit would let you calibrate with any gas. Flush all ambient "air" out of the sensor's way with your backgas, calibrate it, wait for your tank gas to flush out of the sensor's way and start measuring ambient. Not nearly as easy as a lighter, but it'd certainly be a more accurate method.

[Webmaster]

I'd forgotten about that trip!

The lighter test is a quick method of getting a rough idea of whether or not air might be safe to breathe. The lighter test actually reflects the concentration of O2 in the atmosphere. While O2 is converted to CO2 by microbial processes in the subsurface, the final relationship between CO2 and O2 in air is not 1-1, as described in this series of experiments conducted by Australian cavers (http://nhvss.org.au/wp-content/publi...0Helictite.pdf). While the lighter test is better than nothing, and many, many cavers have used it extensively to guide safer exploration of caves with high CO2, the only reliable method of knowing the actual concentration of CO2 in the atmosphere is to buy a CO2 meter.

While CO2 meters used for scientific work can be pretty pricey, if you're only interested in figuring out if you should be breathing the air in a confined space, meters are pretty reasonable ~$100 (http://www.co2meter.com/collections/...table-co-meter). You can transport these in a tube through sumps and then open them up when you arrive on the other side. At $100 each, its not the end of the world if they get flooded....

Finally, I should point out that it is a common misconception that CO2 gas in caves comes from decaying vegetation in caves or from CO2 degassing from dripwater. There is a group of cave researchers (including me) that have been studying the origin of cave air CO2 for several years now - the isotopic signatures of CO2 in cave air (and other lines of evidence) indicate the most likely origins are (A) decay of dissolved organic matter in the space between the soil zone and the water table and (b) respiration of tree roots. The CO2 diffuses through fractures and pores in the rock and accumulates in areas of the cave that are poorly ventilated, such as low spots. Much of our current research is on understanding how the production of this CO2 is linked to formation of caves in places like Florida, Guam, the Yucatan and the Bahamas (or any other location where the limestone is highly porous, which includes parts of the Domincan Republic). In other locations where the rock is less porous (Kentucky, Tennessee, Missouri, etc.) the production of CO2 between the soil and water table exerts an important control on climate records preserved in speleothems.

In the case of air bells between sumps, high CO2 concentrations are sometimes possible due to degassing of CO2 dissolved in the stream - particularly if the stream originates on the surface and sinks into the ground.

My recommendation would be that anyone diving sumps in tropical environments should consider buying a CO2 meter.

Interesting, so the trees ARE trying to kill us.

A number of the bad air caves we encountered were small, shallow pits and generally very dry. Since there was no airflow we assumed that the leaves piling up from the entrance were the source of the CO2.

One of the worst ones I was in was a 30' drop to a small running stream passage. Not much vegetation, but no air flow. The lighter wouldn't light at all there.

[jason]

Interesting, so the trees ARE trying to kill us.

Yes. Just like in the Devonian.

[Aotus]

awesome thread.

[lbattle]

Are there any dry caves/gas pockets that have air so bad you could die/pass out in a few breaths?

My understanding is that it is a larger danger with free diving sumps than on SCUBA, but there is an interesting report in ACA 1999-2001 where the report concludes that (an inexperienced, untrained) diver dove a sump took his regulator out, took a few breaths and died. The conclusion is based on video footage taken by the deceased. The incident was September 17th, 2000 at "an unnamed well" in Goss Canyon, California. If you're an NSS member you can login to the archives and read the report (rather short)... I'll paste the conclusion here:

Comments: Bozanic notes that while Hayden violated
several classic rules of cave diving safety (exceeding his
training and certification, and lacking a proper guideline and
cave diving lights), the videotape indicates that the fatality
was caused by breathing gas from an “air” pocket that was
either too low in oxygen or contained some other gas in a level
sufficient to cause immediate loss of consciousness. He
observes that the incident underscores the potential hazards of
breathing from air pockets in caves.

(Is that allowed? To post ACA materials to a forum like this?)

The source materials for the report cite an article in Underwater Speleology among others... incidentally, is there an online archive for those?

[lbattle]

I say "took a few breaths and died" but I guess I mean he passed out rather immediately and... drowned? So maybe you avoid this situation since you aren't alone...

[phillip1]

When I dive solo I never test the air, I only do that if I am in a team so in case I pass out the someone can shove the reg back in my mouth. Cueva Negra in the DR has many gas pockets, almost all of which are bad it is a super shallow cave with many tree roots all over the place, air tastes super bitter, never took more than one or two breaths there.

Does the fact that water rushes down and that there are basically underground rivers make any difference in air ciruculation? does water temperature play a role

[jason]

When I dive solo I never test the air, I only do that if I am in a team so in case I pass out the someone can shove the reg back in my mouth. Cueva Negra in the DR has many gas pockets, almost all of which are bad it is a super shallow cave with many tree roots all over the place, air tastes super bitter, never took more than one or two breaths there.

Does the fact that water rushes down and that there are basically underground rivers make any difference in air ciruculation? does water temperature play a role

First, Cueva Negra sounds like a great place (at least for scientists interested in CO2....).

Second, the water temperature can exert a control on air quality by controlling the rate of CO2 production in rivers. The rate of CO2 production increases with temperature. We see this in the water chemistry of caves in Florida that reverse flow during floods. Winter floods are associated with less CO2 production and less dissolution than floods that occur in summer. So, if you have a warm river flowing through a cave, there is a greater chance for more CO2 than if there is colder river (this statement requires a number of generalizations). CO2 that is dissolved in rivers will degas into air bells if the CO2 concentration of the cave air is lower than the CO2 concentration of the air bell. Water falls would actually hasten this process by agitating the water (think of how much faster CO2 comes out of a beer after you shake it up).

There are tons of air bells in sumps that have good air - but it only takes one air bell with bad air to kill you. If you're concerned about air quality, the CO2 meters are cheap insurance.

[sskasser]

Interesting, so the trees ARE trying to kill us.

I am Groot.