Dive Computer Safety
Any of the diving computer's that you can buy today at Mike's Dive Store will do their equal best to stop you getting damaged by decompression illness, provided you understand and follow the guidance they give. However, years ago it wasn't necessarily so. Some of them used philosophies that varied widely from the mainstream. I use the term 'philosophy' because it's all based on theory and every person is different so no diving computer manufacturer can guarantee that you won't get a bend. That said, considering the numbers of dives safely done world-wide each year, you've got to be very unlucky indeed.
Most diving computers allow you to add degrees of caution. You may be over-weight or over-age. You may have some health issues. None of these necessarily stop you diving but you should take them into consideration when setting up your computer before diving.
There used to be an Italian brand of computer that advertised the fact that it gave you more bottom time than others. This equated to less safety. Is that what you really want? Thankfully it soon disappeared from the market place.
More insidiously, a very popular brand of computer used to use an algorithm or mathematical model that was intended for no-deco-stop diving to depths less than 30m. That was fine as long as the user was aware of that but of course, often they were not. It gave lots of no-stop time up until the moment that the remaining no-stop time ran out, when it switched to a different table that often then required extensive time at shallow depths before the user could be assured that it was safe to surface. Of course, this usually happened towards the end of a dive at a time when the diver was getting low on air. We saw lots of these computers tied off and dangling beneath boats at around 6m deep while the owner climbed out and went for lunch - albeit feeling a little insecure.
You can still buy computers with this algorithm and provided you intend to use it to manage no-stop times and never go beyond that, they'll probably be fine. However, these same computers now have dual algorithms installed and you can opt for the one that ties in with other mainstream computers.
The fly in the ointment is that few of us bother to read the complex instruction manuals that usually come with computers so I've often witnessed divers doing complex leisure dives unknowingly with an inappropriate algorithm.
I was in Truk Lagoon when my buddy, so equipped found he had 25 minutes more no-stop time while I was decompressing on the trapeze hung under out boat. He continued to dive at around 20m deep and didn't get bent but we have no way of knowing how close to the edge he came.
A lady diving alongside me queried the fact that her two computers of different makes gave widely varying information. I simply later set the offending one to the algorithm that matched the other and she spent the rest of the week much happier.
If you buy a computer fitted with such a dual algorithm, be sure ask the person that sells it to you to set it to the algorithm appropriate to the type of diving you'll be doing; shallow no-stop dives or dives where you go a bit deeper. It might be agued that the second type errs on the side of caution. I'd say it does no harm to hang around at 6m or less as might be mandated, provided you've got sufficient gas in your tank. Stay away from the edge!
Happy diving. - John Bantin
