Dive safe! A short story from a chamber operator

[BlueTrin]

Re tracking of oxygen exposure, see this page from the Teric manual:
View attachment 529806

Does it use the half life formula for periods which are not a multiple of 90 mins ?

 

[scubadada]

Does it use the half life formula for periods which are not a multiple of 90 mins ?

Of course it does, it is a proportional decrease or increase in the oxygen elimination before the next dive

 

[ThatDogDontHunt]

Does it use the half life formula for periods which are not a multiple of 90 mins ?

Yes. Half life formulas are continuous functions. Nothing magic happens just after 89 minutes and 59 seconds. It is a gradual continual process during each 90 minute half life.

Half-life - Wikipedia
Exponential decay - Wikipedia

 

[DawgFan]

Re tracking of oxygen exposure, see this page from the Teric manual:
View attachment 529806

The Teric manual text says it turns red when greater than 150%. The picture shows it red at 101%. Is the 150% a typo?

 

[jgttrey]

I like that idea! That way you're being given accurate data in real time, plus if anything does go wrong your "black box" computer can help accurately reconstruct the accident and help you to decide on new limits going forward.

I think my resistance to the idea of using a more conservative setting is that I wouldn't know how much time I really had left if, say, my buddy was having a problem, or someone else in the group (or some rando who happened to be in the water at the same time) and I had to make a quick decision about how much personal risk I would accept to try to help them. But I'm not actually familiar with how the more conservative settings work, so maybe that concern is unfounded?

A few thoughts, not all of which are in relation to the quoted posts:

1. I hate computer alarms. Except for the vibrating kind, they are really annoying. Everyone looks around for who is beeping and trying to figure out if it's a real problem or not. They also create a false sense of security that the computer will tell me if I'm doing something unsafe. If you are checking your gauges with anything like the frequency you should, you don't need one. I worry about the diver who feels free to chase the fishes down the wall relying on an alarm to keep him/her safe.

2. Dive planning/conservatism isn't that hard. Pick a suitable gas, analyze it and accurately program the computer. You should know the MOD by heart. See point #1.

3. If you want to be more conservative, use the conservatism settings on the computer -- that's what they are for. Or, just leave computer as is and dive conservatively by shallowing up when you get within 10 minutes of your NDL, or whatever figure you're comfortable with.

4. Telling the computer you are on air when you are on nitrox is a poor practice for reasons identified by others. I think the computer should be programmed to give you accurate information - always. The conservatism is something you address by diving conservatively or instructing the computer to apply conservative factors, not feeding the computer b.s. about what gas you are using.

 

[BlueTrin]

Yes. Half life formulas are continuous functions. Nothing magic happens just after 89 minutes and 59 seconds. It is a gradual continual process during each 90 minute half life.

Half-life - Wikipedia
Exponential decay - Wikipedia

Yea my question was about the Teric, not about half-life

 

[EFX]

Dive nitrox. Especially if you are over the age of 40. Enriched air means you are absorbing less inert gas during your dive. When you dive nitrox and use an air profile, this makes your dive safer.

Great article Tony. My only criticism is the advice to dive nitrox and set your computer for air. Divers need to know exactly what their computers are telling them for the gas they are using. I would suggest if you need more conservatism then set your computer to a higher conservative setting and set the gas to the gas you are actually using.

 

[kafkaland]

So the idea is to be calm and zen when at depth. Don't work hard. On your safety stop, do some light exercise. As in, swim around a bit. Don't do a cross-fit routine.

Whether light exercise on the safety or deco stop is advisable is still a bit controversial. To get a nitrogen bubble to grow, you need two things: a supersaturation of the tissue and a nucleation point, usually a small gas nucleus. You can reduce the former by making offgassing more efficient, and by increasing blood flow you will accomplish this. But higher blood flow means also more turbulence especially in the larger blood vessels, which increases the formation of small gas bubbles. Those tiny bubbles can get lodged in the capillaries of deeper tissues, serve as nucleation points and grow into big bubbles there. Which in turn can result in the clinical symptoms of DCS.
Empirical evidence supporting one or the other for recreational diving is scant, for all practical purposes it doesn't seem to matter, so I would just do what feels best to you.

 

[Jay]

The local chamber in our public hospital has 'open nights' for divers. One of the purposes of having those nights is to make coming to the chamber or calling for advice less of a hurdle. Aside from the Doctors and Nurses presenting at the night DAN was also there.

Their old old chambers are like the OP's, but the newer ones are much more inviting. The newest one is basically a large room, many chairs, nice portholes.

They did highlight and showed us many dive profiles of avid divers who had done sensible, well inside limit (no deco) dives who ended up doing some rides.

FYI: The Australian Government has Reciprocal Health Care Agreements with the governments of the United Kingdom, Sweden, the Netherlands, Finland, Norway, Malta, Italy, Belgium, the Republic of Ireland and New Zealand.

 

[caydiver]

In the last couple of weeks have spent quite a few hours on duty. We can go months without being called. Ironically both most recent incidents were with the same op. No oxygen on was supplied on board. Neither incident was mild. Both cases were divers who normally dive Nitrox but were not or mixing. Reason heresay so it is what it is. Both were experienced divers one of whom was doing 2T mornings with shore dives in afternoons. The other had done only 1T for a few days but 3 dives the day she became ill. Hugely unfortunate one thought DAN was current and the other never had it. More unfortunate is both like so many of us never think it will happen to them. They were simply doing what they have always done. My experience doesn’t answer any questions but suggests that just because you got away with doing something for years doesn’t mean you can always get away with it. I am very proud of my ability to glide up and over and back down again over fingers. Might be rethinking that skill