So why do so many divers die with their weights on?
Try an experiment. Go to any of the annual DAN fatality reports and go through the description of the fatal events and try to fit dropping weights into the scenario as a lifesaving measure. I did that myself for several such studies covering several years and found that in fewer than 10% of the cases dropping weights MIGHT have made a difference. Someone said in any earlier post that panic was the single most important factor in fatalities. It isn't. Cardiac events lead the causes, and when you pass out from a heart attack, you aren't going to drop your weights, and dropping them won't bring you back to life. The single most common incident causing a death is indeed related to panic--the diver makes a panicked ascent to the surface, usually after going out of air, and gets a fatal embolism from that panicked, breath-holding ascent. Again, dropping weights would have made no difference; in fact, it might have made the possibility of death even greater. There are then entanglements and other similar issues. Of the 10% I found where dropping weights MIGHT have made a difference, the reason I included them was usually because there was not enough information to get a really clear idea what happened, which is why I stressed the word MIGHT
So yes, the overwhelming majority of scuba fatalities had their weights on, but that does not mean that failing to drop the drop those weights was a factor in their deaths.
I agree that we can not
assume there is any relationship between a diver found dead on the bottom and the failure to drop ballast. I also think we should pretty much assume that most significant cardiac events which occur on the bottom are not survivable, but that does not mean that ditching lead is not critical in some situations.
In order to understand the importance of dropping lead, it would seem necessary to also look very carefully at the NON-fatal accidents and incidents. How many people were saved, or avoided sinking further into the incident pit by dropping ballast? That is the type of statistic that would seem most relevant to determine he efficacy and safety of dropping lead.
I'm not a statistician, but it seems to me that in order to understand the importance (and negatives) of dropping lead at the surface or at depth, you would want to try to look at the number of people who died from embolisms (or DCI) that dropped lead at depth (and maybe assume a larger percentage of those cases were caused by dropping lead) and compare that to the number of people who have "walked away" from the situation with zero (or minimal) injuries. For example, if 10% of the people die and 90% of them walk away, then we might be more comfortable with the concept of dropping lead at depth.
Also, the discussion of dropping lead (at depth) tends to be very polarizing and always seems to be excessively biased from the PERSONAL perspective of the diver. More specifically, the significance (or danger) of dropping lead in a warm water situation (with minimal exposure protection) is probably small because we are talking about a "modest" amount of lead (maybe 3 to 10 lbs or so). I typically dive with zero to 6-8 lbs of lead on a belt - so dropping the belt would be a no brainer for me if it was a no-deco dive and I thought it was possibly necessary.
Conversely, if you are wearing a 25-lb weight belt and drop the entire amount, the resulting buoyancy change can most definitely be significant and dangerous. In any regard, we are constantly hearing the overly simplistic, comment that ditching lead at depth is going to send you rocketing to the surface. NOT a valid assumption in all situations.
I personally feel that for recreational diving, having 6 or 8 lbs of ditchable lead is much safer than having all lead integrated and unable to be jettisoned on the bottom.