Diving myths taught for safety?

[swimmer_spe]

Just this past Saturday off the coast we did two deep dives back to back. Both involved some deco. Once again we seemed to cheat death.

I wonder, just how close are those tables? I mean, if it says bottom time of 20 minutes, and you stayed for 25, 30, 40... really, at what point would you get bent?

Not that I would be stupid enough to be the guinea pig to find out.

 

[boulderjohn]

I wonder, just how close are those tables? I mean, if it says bottom time of 20 minutes, and you stayed for 25, 30, 40... really, at what point would you get bent?

Not that I would be stupid enough to be the guinea pig to find out.

Obviously as you go beyond limits, the odds get worse and worse. There is no definitive data on that, in part because every individual is different and because we honestly still don't understand DCS well enough. The research that led to the PADI tables was published. It showed that staying within those limits was very, very safe, but not 100% safe. Many divers were tested in that research. If you decided to do a long series of dives to see what it would take to get you bent, you will have data to show what it took to get ONE diver bent on that ONE day under whatever condition he was in when he did that dive.

 

[bl6394]

I wonder, just how close are those tables? I mean, if it says bottom time of 20 minutes, and you stayed for 25, 30, 40... really, at what point would you get bent?

Not that I would be stupid enough to be the guinea pig to find out.

That's one of the wonderful things about DCS - it's not deterministic - even for the same person, diving the same profile. One day - you may be young, fit, rested, hydrated, in warm water - the next time - one of these variables changes - or you climb a steep hill after the dive - and you're bent. Same person, same profile - different outcome. Now you start comparing different people - it introduces even more variables...

Best to stay a bit conservative - cause you won't know exactly where that line is on any given dive.

- Bjorn

 

[BDSC]

I wonder, just how close are those tables? I mean, if it says bottom time of 20 minutes, and you stayed for 25, 30, 40... really, at what point would you get bent?

I was thinking about that very thing this past weekend when I was hanging to let the deco obligation clear. My thought is that overall, tables and/or computers are in general conservative. So let's say someone does a dive and your computer says you need to do a 3 minute deco stop and you don't. You just surface. How likely is it that you/anyone would actually get bent? How about if you blow off a 5 minute obligation....etc. I know everyone is different and can be affected differently by doing such but I too was wondering at what point would you really be pressing your luck.

Next time I see Dr. Neal Pollock at DAN headquarters, I'll see what his thoughts are.

 

[MrChen]

Has anyone mentioned turning the SPG away from your face when you turn the tank on? I do it out of habit but in 43 years I've never seen one explode.

DM during my OW said he had one shatter once. He said if he had been looking at it, glass would have been thrown towards his face.

 

[swimmer_spe]

DM during my OW said he had one shatter once. He said if he had been looking at it, glass would have been thrown towards his face.

When you are dealing with ~3000psi, it is always good to be a little more careful. On my job we deal with that kind of pressure, and if we suspect a leak we grab the nearest broom. That kind of pressure will cut off the broom handle. Better it than me.

 

[iluvtheocean]

When you are dealing with ~3000psi, it is always good to be a little more careful. On my job we deal with that kind of pressure, and if we suspect a leak we grab the nearest broom. That kind of pressure will cut off the broom handle. Better it than me.

so looks less like a myth and just good sense for something that *might* happen. Like swimmer said, better safe than sorry when dealing with high pressure.
i think the air cannons that they use on mythbusters -- many of their tests are done at less than 500 psi. if 500 psi or less can produce those results, i'd rather not risk anything @ 3000.

 

[themagni]

I was generalizing. I do dive within my limits of experience and instruction.

Before I signed up for my AOW, I have dove to 90 feet, did a few night dives, did an ice diver course, solo dove....

How does one find their limit without hitting it? However, I am not going to do anything I know will kill me.

By surprise and then spending some time in a box. Might be pine, might be steel. Hard to say.

---------- Post added May 22nd, 2013 at 04:30 PM ----------

I wonder, just how close are those tables? I mean, if it says bottom time of 20 minutes, and you stayed for 25, 30, 40... really, at what point would you get bent?

Not that I would be stupid enough to be the guinea pig to find out.

It's statistical analysis. It's like when you get a part that's rated for 10,000 operations or a light bulb that will burn for 3000 hours. They don't test them all, they model stuff and do math. A couple pieces out of the batch may be tested to failure (might be where the original tables came from) but you're just following a mathematical approximation of what's probably safe 99% of the time, given certain conditions.

Go outside the assumptions and you could break earlier than you expect.

 

[AfterDark]

I wonder, just how close are those tables? I mean, if it says bottom time of 20 minutes, and you stayed for 25, 30, 40... really, at what point would you get bent?

Not that I would be stupid enough to be the guinea pig to find out.

The USN had plenty of guinea pigs and they found out. Some people can overstay an NDL and be fine others can get close but not over and be in trouble. The sailors that volunteered for those experiments were in a lot better shape than most of us are so that needs to be factored in too. I've also played the conservative end of the limits and so far no problems.

 

[swimmer_spe]

The USN had plenty of guinea pigs and they found out. Some people can overstay an NDL and be fine others can get close but not over and be in trouble. The sailors that volunteered for those experiments were in a lot better shape than most of us are so that needs to be factored in too. I've also played the conservative end of the limits and so far no problems.

I heard about that.