Skin Bends - Lessons learned

[vladimir]

Patent Foramen Ovale

 

[Ken Kurtis]

Unfortunately the reaction of some divers to their computer going into deco is to look for a more liberal algorithm. I see people looking for the most liberal computer, which is really saying, I want to increase my bottom time and sacrifice my margin of safety.

Again, NO. It is not saying that. At least not with everyone seeking safe, liberal computers.

In Audrey's case, she told me that was EXACTLY what the issue was. But she certainly didn't see it as sacrificing any margin of safety.

She had been diving for years with a Cobra and she got tired of it telling her to come up long before her friends with more "liberal" computers. So that's why she switched to the Proplus2 - it was going to give her more bottom time overall. This trip was the first trip she had done on the new computer. (I think she may have already done 5 dives on it but certainly not a weeklong live-aboard.)

It is saying I want to know where the edge is and I'll manage how close I'll get to it and how careful I will be when I approach it.

The problem with that logic is that the only way - in terms of dive profiles/computers - to know when you've reached the edge is to go over it and by then it means you're bent and it's too late.

I'm always reminded that the first commercially viable dive computer was called the Edge because it eliminated the safety margin built into dive tables (multi-level dives computed as a square profiles) and took you to the EDGE of decompression limits/safety.

- Ken

 

[MaxBottomtime]

It was also known as the Bend-O-Matic for the same reason.

 

[Ken Kurtis]

It was also known as the Bend-O-Matic for the same reason.

Not the Edge.

The Bends-O-Matic was the nickname for the SOS Decompression Meter that was developed in Europe and distributed in the US by Scubapro. The nickname came from the fact that people were (supposedly) treated in chambers and came in wearing the device which was insisting they shouldn't be bent.

We used to have one at Reef Seekers (I think my ex-biz partner Bill Wright has it now) that we'd pull out every now and then to show people. And I'm pretty sure that Karl Huggins has one at the Catalina Hyperbaric Chamber that he pulls out every now and then and tests against modern-day computers.

You can read more about the Bends-O-Matic and other early computers in the Skin Diver archives with an article written by Daryl Carson:
2000-05 Dive Computer Evolution

- Ken

 

[freewillie]

Having just completed AOW with deep dive, the official #1 reason according PADI text book divers get bent is due to diver error. That includes pushing the limits on depth and time. Pushing your computer to the edge, liberal or conservative is to flirt with the chamber.

Keep in mind that dive tables are like one size fits all clothing. For the majority it will fit okay. For lucky few will fit really well. For the unlucky few won't fit at all.

Dive tables are designed to fit the majority. Individual differences will affect the algorithms as well including age, weight, medications, and dehydration. Notice these will affect the individual and is not the same as saying it is the cause of being bent. They can be the proverbial straw that breaks the camels back. If you push the limits these may be the difference between not being bent and spending time in the chamber.

 

[Gilldiver]

Not the Edge.

The Bends-O-Matic was the nickname for the SOS Decompression Meter that was developed in Europe and distributed in the US by Scubapro. The nickname came from the fact that people were (supposedly) treated in chambers and came in wearing the device which was insisting they shouldn't be bent.

The SOS actually followed the US Navy air tables fairly closely on the first dive - now the 2nd dive was a crap shoot and was where people usually got bent. As for the Edge, it is a good air computer and takes one or two pounds off your weight belt which is why it is called "The Brick."

 

[redacted]

The problem with that logic is that the only way - in terms of dive profiles/computers - to know when you've reached the edge is to go over it and by then it means you're bent and it's too late.

I'm always reminded that the first commercially viable dive computer was called the Edge because it eliminated the safety margin built into dive tables (multi-level dives computed as a square profiles) and took you to the EDGE of decompression limits/safety.

- Ken

While you may not be able to know exactly where the edge is, you can fairly easily know which computer puts you closer to it and which puts you further away. Hence the dive computer liberal to conservative scale. Yes, I do make the assumption that all modern dive computers are considered "safe". I have little doubt that assumption is correct or we would be seeing data (not just the rare anecdote) providing statistically credible evidence to the contrary along with recalls and legal actions.

Of course, one can opt for the most conservative dive computer and feel more confident diving to its limits. I'd suggest that routinely diving any computer to its limits without taking appropriate precautions is just asking for trouble. Those precautions include slow ascents, multiple stops for deep dives, and extended rest stops. Of course, if a diver does not have the skills and discipline to do those things, they may realize a measurable margin of safety by opting for the conservative, more restrictive computers. But divers with the necessary skills and discipline can take advantage of the additional freedoms afforded by more liberal computers.

 

[JG109]

If you have the air, I always recommend a 5-10 minute stop (conditions etc permitting). As an added bonus, the day a diver has an issue and ends up w an unplanned deco hang, it is not their first hang and they are already accustomed to a longer hang.

 

[caseywilson]

Excellent post for me a newcomer to diving. Sadly, tons more than I've ever gotten from my instructors.

 

[bleeb]

While you may not be able to know exactly where the edge is, you can fairly easily know which computer puts you closer to it and which puts you further away. Hence the dive computer liberal to conservative scale.

I'm wondering whether this is an accurate definition of liberal/conservative. To be precise, I suspect that, in creating the different programs, each individual manufacturer is not so much thinking 'the hypothetical (and not precisely knowable) edge is there and I'll design my software to stay such-and-such a distance from it'. Rather, the differences between computers is more because the manufacturer has used a deco model and written a program which then defines an edge which is different from a different manufacturer's program's edge. Although additionally moving closer or further from each computer's nominal edge happens, it's likely not the dominant driver for differences.