Here's a repost of my post on the last "Solo Diving" thread. Still applies
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First, I must tell you that I do occasionally dive alone - usually very early in the morning when no one else is willing to get up and go. - BUT -
When I do, I am betting my life that I will not get entrapped, and that I will not have some unanticipated incapacitating episode on that dive. These two are independent of redundancy, and while conservatism can all but eliminate entrapment, the risk of sudden incapacitation can only be marginally reduced.
I will provide two recent, local (Lower Alabama), specific examples which may help you make up your own mind when considering whether it is "safe" to go it alone.
(1) One of my boyhood friends was cleaning his pond - alone, in just over five feet of water. He had some kind of attack - probably stroke or heart attack - and drowned. We will never know if he could have been saved from the attack because he drowned first. Had he had a buddy, he would likely not have drowned. This man was in "excellent shape" - trim, ate right, regular exercise, superior swimmer and diver. Still, we buried him.
(2) Two spearfishermen were diving from a boat out of Gulf Shores - on the first dive, one had equipment problems on entry and elected to abort the dive. The other decided to go on solo. About fifteen minutes later, the boat driver and the other diver saw a huge freeflow of bubbles at the surface, followed shortly by the diver popping up, drowned. CPR failed. When he popped to the surface, he was wrapped up in the shaft line of the speargun, regulator out of his mouth and both arms pinned with the line. We believe he shot a big amberjack that wrapped him up and knocked the regulator out of his mouth - unable to get to his primary or independent second regulator and unable to jettison his weights, he'd started an emergency swimming ascent (we don't know how long the fish stayed on the spear and what affect that had on his efforts to get free/up); the last conscious thing he was able to do was get free enough to reach his power inflator, too late. Had he had a buddy, he would likely not have drowned. Again, he was in excellent shape, an experienced diver and spearfisherman (although obviously not experienced enough to shoot only things small enough for him to handle alone), and still died.
Note that in both these cases there was no equipment failure, no lack of redundancy, no deficiency in training or in fitness to dive. The incapacitation in the first case was a complete surprise; the entrapment in the second avoidable but nevertheless unexpected. In either case a buddy would likely have prevented the drowning.
Rick