SCUBA Diving in Mexico With Robert Boyle

For those not in the know:

Vary practical knowledge if you’re a diver. 40 minutes of air at sea level turns into 20 minutes at 33 feet, or 10 minutes at 66 feet, or 5 minutes at 99 feet. Any deeper and you narc out and just don’t care.

So, does it work in reverse? Let’s say Robert & I ate a hearty dinner of cheezy beans & rice the night before a big dive and we’re feeling a bit gassy. We have some big tanks, maybe a re-breather or something, and are cruising at 99 feet for a good 20 minutes. Mr. Boyle passes an impressive quantity of intestinal gas, a bomb that would have cleared a room at the party last night. At depth, it’s a regular monster fart. Assuming the bubble remains intact on its ascent (heh…scent!) is it 4 times as big when it greets the outside world?

And let’s say I’m a bit more Victorian about it and like to keep mine in until I’m in more discreet surroundings. Is it going to expand a bunch while it’s in me? Cuz that’d be a hell of a party trick!

Gases do expand as they rise through the water column, yes. Assuming that’s what you want to know.

Of course at depth, the volume of gas you produce would be less because of the pressure. But, assuming release of said gas is triggered by the accumulation of a certain fixed volume, then you would fart the usual amount, which would be 4x the usual amount when it got to the surface.

Oh, and you’re wrong about the specific numbers. The volume isn’t cut in half every 33 feet – it’s just inversely proportional to depth. So 40 minutes at 1 atm (surface) is 20 minutes at 2 atm (33 feet) or 13.3 minutes at 3 atm (66 feet) or 10 minutes at 4 atm (99 feet). Assuming constant volumetric consumption rates, of course.

So if I’m holding in a big one at 100 feet, what happens as I ascend? Will I explode? Or is it likely just to force its way out like a gasseous bulldozer?

From experience - you’ll feel full on the way up, and it will come out. Actually, I had no intention of holding it in, since it’s pounded into your head that you shouldn’t hold your breath while diving, so holding in gas didn’t sound good either. I don’t know if your will would break before your intestines do if you’re really insistent on holding it in.

If you’ve ever struggled to retain a fart, then that’s basically what you’re dealing with. When the volume gets large enough, it’ll open the door all by itself.

Not necessarily; pockets of gas far away from the door can get painfully stuck.

My dive instructor told us to avoid gassy foods before a dive.

Having a fart stuck inside your wetsuit can be an interesting experience as well - you can sometimes feel it moving around. Like up your back and into your hood.

I learned on this board (sorry no cite, but it’s been mentioned in many threads) that this factors into high altitude flights as well. Any gas in your digestive system expands, causing discomfort until it is expelled.

A fart in a wetsuit is nothing like a fart in a drysuit. The seals will keep things contained, and the results of that will be discovered when you’re back on board the boat, and you peel the thing off. The faint of heart should be warned to move upwind to the other end of the boat before this happens.

I really don’t think it’s going to be too much of a problem. Unless you swallow air while diving, the gas in your gut when you’re on the bottom will be the same gas you had when you started the dive. It fit there at the start of the dive. It got compressed during the dive. It expands back to original size at the end.

If you dive deep, say over 60 feet, your bottom time will be less than 60 minutes. That’s not a lot of time to churn up a large load of methane.

If you stay shallow, and you don’t burn through your air, you could conceivably be underwater for well over an hour. But even if your GI tract goes into overdrive and creates a lot of gas, I doubt that it’s going to expand so much that you get into trouble.

Finally, all divers have slow ascent rates drummed into their heads from the beginning of their training. 6o feet per minute was the fastest allowed, and slower was better. I learned to dive on a 2-hose regulator, and I was taught to ascend slowly hand over hand up the anchor line, counting “1-one thousand, 2-one-thousand” as I went foot by foot. And now, don’t the new-fangled dive computers have ascent rate alarms built into them?

Bottom line - I don’t think this is the thing you need to worry about. I’d be more afraid of the great white carp.

What happens if you get the bends, while diving in Mexico? Are there decompression chambers available? Or is it a case of “tough luck”?

I’m not sure about Mexico, but usually there’s a hospital with a pressure chamber somewhere within helicopter distance of most sites (the heli will fly low in order to not make things worse). Hyperbaric chambers are commonly used to treat burn victims (by immersing them in an enriched oxygen environment under pressure to promote dermal healing), so their presence isn’t as unusual as one might think. Some large dive boats also have their own chambers, as will many oil rigs.

Worst case scenario (and this is considered damn risky, but is employed by some navies) is to simply lower the diver down again at depth and let them deco under pressure. The hazards of this are obvious.

On the other hand, get bent badly enough and you’re dead by the time you hit the surface anyway.

Ralf, I’d like you to meet my friend: double tank configuration :wink: And in turn his friend, the complex but deadly (may kill without warning ™), Mr. CCR.

Hang around at 40m for more than a few minutes and rack up a deco obligation and you’re easily up for a pretty long dive.

They do indeed, bless their little electronic souls. A pretty good rule of thumb is also to not rise faster than your own bubbles…but as you said, the slower the better. I was actually taught to rise at 9m per minute, i.e. about half your rate.

Kombat, while I didn’t say it, I was referring to more sport-diving scenarios. Rebreathers and multiple cylinders can indeed extend bottom times so that you can go way beyond the traditional no-decompression time limits. I know these are popular options with some divers, but most sport divers don’t use them. I have spent my time hanging on the line blowing off nitrogen, wishing I had a newspaper or a checker board or ANYTHING to pass the time. After awhile, it seemed I spent more time hanging on the line than I did on the wreck, and I decided decompression wasn’t really worth it most of the time, unless there was a specific goal to accomplish at that depth for that length of time. I ended up breaking my duals down and staying shallower for longer, and enjoying the diving more.

When I certified, 60 feet per minute was the standard, but later I was taught that slower was better - 30 feet per minute. Sorry for not making that clearer.

Some areas have their own chamber. Cozumel used to have one, but its been years since I was there. I think I remember that they funded it with a “dollar a day” tax on divers, or some such.

You can also buy evacuation insurance, where if something happens, someone will show up with a private, pressurized aircraft and whisk you away to the nearest chamber, or wherever you need to go to be treated for whatever injury you’ve had.

I once did a chamber dive at a local hospital. The chamber would seat about 8 people at a time, and had a man-sized lock to allow a doctor or nurse in and out. We did a brief set of cognition and manual dexterity tests first - a series of math problems, and sorting out and putting different sized bolts together into a metal plate with different holes. Then we did a “dive” to about 110-120 feet, and did the same test. Some people actually did the tests FASTER at depth. Everyone got Donald Duck voices. And one person started giggling at anything and everything. We think all the nitrogen in the chamber moved down to his end of the pot.