Re: Are computers Really Safe?

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Posted by Ken Kurtis on October 01, 2002 at 12:21:38:

In Reply to: Are computers Really Safe? posted by Captain Tim on October 01, 2002 at 10:34:50:

Tim asked: "Here is the question. Just how safe are computers, and are some worst than others?"

I think the computers are relatively safe. It's the divers that are dangerous.

Excellent question, Tim, and hopefully will produce a lively dialogue.

Tim and I have discussed this before and I agree with his basic premise that people are diving computers without a clue and just watching the numbers without any real knowledge or understandsing of what those numbers mean or how they are being derived. That's dangeous, IMHO.

I also think, in general terms, that computers can be considered safer than tables since they eliminate one of the bigger causes of getting bent on tables, which is reading them wrong by crossing columns or rows. As Andy Pilmanis, former director of the Catalina Chmaber used to say, "Computers don't lie and they don't forget."

However, I think Tim's also right in stating that computers are NOT safer than tables in that they allow, due to the multi-level nature, more time spent in the water. More time = more nitrogen = more chance of getting bent.

Don't forget that the first commercially-available dive computer was called the Edge because it took divers to the the edge of safety. Because tables, since they're 2-D instead of 3-D, always model a square profile even though you do multi-level, there's an inherent safety/fudge factor built in. Computers, on the other hand, try to model you based on your exact depths and times within the confines of the algorhithm leaving much less margin for error.

No one keeps stats on which models are safer than others (perhaps Karl Huggins could offer some insight) but my impression is that there's not one model that's bending people with a greater frequency than any other. By the same token, given the relatively small number of bends hits each year (roughly 1000 divers US - out of an estimated 2.5 million divers making 25 million dives total) you may not be able to generate a statistical reliable comparison.

I would take issue with a couple of things Tim said.

I don't think the bends rate has changed significantly over the years, either nationally or locally. Seems the national numbers have stayed pretty much the same (maybe even delcined a little). And I think the number of local treatments (and again, perhaps Karl can contribute something here) has stayed pretty much the same year-to-year.

I personally have not observed a failure rate of one comptuer (on average) per trip. That's not to say they don't fail (and it's usually a battery problem, not a failure of the workings of the computer itself) but I don't think it's that frequently. To my way of thinking, battery probems don't indicate computer failure, but user error.

As far as the diver with the computer locking him out, as far as I know, a computer will NOT do that based simply on a fast ascent let alone just the last 10 feet.

A computer WILL lock you out, however, when you go into deco and then blow through the required deco stop(s). It's the computer's way of hoping to prevent you further potentially injuring yourself. If the computer was truly "locked out" (and remember that some models - like the older Pelagics - simply go into a "surface mode" for 10 minutes which prevents you from accessing data but which, to the untrained eye, might look like a lockout), it would be locked out due to deco violations, NOT due to ascent violations.

As far as the missed deco stop, I'll just throw in the thought that this is one reason that I personally feel deco diving can be so inherently dangerous. Mismanage your air/gas supply and your choices are drowning or getting bent.

But I also think in this case you dodged a bullet. Personally, I would never advise a diver with missed deco to go back into the water. I think even the Navy has gotten away from Ommitted Decompression protocols.

Once at the surface, you may have already have experienced enough of a pressure gradient change that the bubbles have already formed or are forming. Going down to 15' to "finish" your deco won't do much since, if you were being treated, they'd need to start you at a depth of 60' and then bring you up.

On top of that, it just doesn't seem like a good idea to put a diver who's potentially got a medical problem (bends) into the water. Think Mia Tegner. Much better, IMHO, to keep him/her on the boat and either put them on O2 immediately and call the Chamber, or at least monitor them for any signs/symnotoms of DCI and then get treatment if they appear.

Anyhow, those are my thoughts. Great questions, Tim. Who's next????

Ken Kurtis
NAUI Instr. #5936
Co-owner, Reef Seekers Dive Co.
Beverly Hills, CA

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