Toxic Gas Pockets!

Cave Diving

- NATALIE GIBB

What’s your biggest fear about cave diving? Cave collapses? Getting stuck in a restriction? Getting lost? Running out of breathing gas far from the exit? Total darkness? While these are legitimate, albeit unlikely risks, they can generally be avoided through proper dive planning, procedures, good judgement and common sense. You should not, for example, continue into a cave if pieces of the ceiling are falling off around you.

However, there are other risks that, while equally avoidable, are not covered extensively in all cave training manuals. One such danger is gas pockets that appear to be filled with air but may be unbreathable due to low oxygen content or toxic compounds. These have always fascinated me, probably because they are uncommon in Mexico, where I live. I have never found one before.

Recently, however, I finally encountered a toxic gas pocket while working on a resurvey and clean-up of one our old exploration projects. This sounds horrifying, but I am so curious about caves and the aquifer that I was rather excited about it.

I’d just about finished the resurvey of the northwest section of the cave. All the old lines were charted on my stick map, and I had checked all the possible exploration leads except for one. My exploration partner Vince thought that there might be a small passage heading south off a tiny loop to the east. I agreed to check it on my final survey dive in the section.

I scootered over to the tiny loop. Vince was right! There was a lead going south. It looked like it would take me to the backside of a massive, semi-flooded chamber we had already explored.