Whatever circumstances lead to a diver dying underwater, the ultimate physiological cause of death is usually drowning. Most diving fatalities occur to ordinary recreational divers. Usually they are not solo diving, but accompanied by a buddy or part of a group. Some are under instruction. However at the time that they die they have become separated. They die entirely alone.
If you expect that a search will locate you and save you, forget it now. If you are at 30 m and have just stopped breathing and your buddy ascends immediately that he notices you are missing and does not make a 3 minute safety stop or have to decompress it will still take two to three minutes for him to reach the surface. By then you will have stopped breath holding and will have begun inhaling water. During the next three minutes it takes him to redescend your heart will have arrested. If he locates your body in the next sixty seconds and brings you to the surface in the next three minutes you will almost certainly be irreversibly brain damaged should attempts to resuscitate you prove successful. According to DAN's Dive and Travel Medical Guide the total time of submergence with chance of recovery, then, can be expected to be 10 to 12 minutes at most.
In truth most searches are unlikely to save lives. How could they? Once a diver stops breathing there is no bubble trail to mark his position. A freeflow will empty a tank in minutes again leaving no tell tale bubbles to follow. Most recreational divers are not trained, practiced or equipped to carry out a swift and effective search. Most divers have become separated from their buddy at some time and have at best followed the one minute rule of searching along the bottom for sixty seconds before ascending or more likely continued their dive assuming all is well. Even if a diver does ascend immediately they usually wait several minutes before raising the alarm or redescending on the assumption that their buddy is also on the way up. Usually the diver does not think to or cannot take bearings to help him relocate the point on the bottom at which he lost his buddy and combined with currents causing him to drift off station realistically has little hope of quickly finding the missing diver. So a rescue attempt may more accurately be described as an exercise in body recovery.
The searchers may also be forced to take chances, exposing themselves to beginning the dive with partly used gas supplies, short no-decompression limits and pressed into DCI provocative profiles, possibly chilled and if part of a buddy team rather than a group morally obliged to dive solo.
A better option, in my opinion, is to take executive action. Do something proactive for yourself that might save your life. Drop your weight belt. Contrary to a critical comment in this magazine (this article was first published in Dive International Magazine), what we are talking about is exactly an ejector seat---a last resort that might just save our lives when doing nothing will result in almost certain death.
Objections to dropping belts revolve chiefly around the ascent rate. Many divers assume that a buoyant ascent will actually kill them through decompression illness or lung expansion injuries. So they apparently prefer to drown. Ascent rates are comparatively slow these days (typically 6-10 m/min in shallow water). However back in the mid 50s Doug Fane of the US Navy Underwater Demolition Team was arguing for a 30 m per minute minimum ascent rate for his divers. Commercial divers used to undergo a test during their medicals to establish that they could exhale fast enough to ensure they could avoid lung expansion injuries in case of a rapid ascent or pressure change from passing swells in shallow water.
In reality the ascent rate a diver will achieve by dropping his weight belt depends on many factors. If the diver is overweighted and has added lots of air to his BCD or dry suit to compensate, the ascent will initially be very fast. If the diver is properly weighted, the speed of ascent may initially be much slower. Much depends on the increasing buoyancy of expanding gas in the divers suit and or BCD. Certainly most divers will have reached, and this is perhaps an unfortunate choice of words, terminal velocity by the time they hit surface.
So what is terminal velocity? According to leading dive safety researcher Glen Egstrom, writing in Stress and Performance in Diving, it is around 70 m/min using a fully inflated BCD with 20 kg of lift. That's certainly fast, but is it really unsurvivable?
To answer that question with any certainty we must look to a group of people who have already chosen fast, buoyant ascents as a way of escaping certain death. Submariners. At HMS Dolphin in Gosport a 30 m water filled tower is used to train submariners to make buoyant ascents on a single breath. Once they leave the bottom of the tower, their life jackets carry them to the surface at about 70 metres per minute. Their track record is admirable. 50,000 buoyant ascents for just 25 accidents with no fatalities. No doubt the Navy's high standards of training and the speed at which a trainee can be placed back under pressure in a recompression chamber (a matter of seconds) account in part for this. None the less, 49,975 ascents were made without incident.
In truth many recreational divers would not attain this speed. Few BCDs these days contain 20 kilos of lift, 12 to 15 is more likely. and that assumes the BCD fully inflates during the ascent. Simply dropping the weight belt is unlikely to create such a fast ascent rate. A properly weighted diver using just a dive skin may rise quite slowly.
In fact there are many documented cases of divers either making deliberate buoyant ascents or involuntary ones due to a weight belt falling off that resulted in either injuries that were successfully treated or were injury free entirely. I suspect that more run away ascents take place than are actually reported and so would expect to see a bias towards ascents resulting in injury in the statistics. In fact all the incident reports I've looked at contain more rapid ascents that did not result in injury than did. Further evidence that a rapid ascent is usually entirely surviviable. These ascents occur through human error such as entanglement in delayed SMBs or gear failure when a dump valve fails. And of course some result because the quick release buckle on weight belts is prone to tripping unexpectedly.
On advice, I took to using two cam buckles to secure my weight belt during penetration and decompression dives. Weight belt buckles are designed for easy jettisoning and the downside is that they can trip unexpectedly. Inside a wreck, cave or under ice you end up pinned to the roof. During decompression you'll crash your ceiling and probably get bent. After my belt tripped in 15 m during a normal open water dive I took to double buckling every dive. I don't want my belt dropping unintentionally. Many critics seem unwilling to ditch their belts in a do or die situation but are evidently perfectly happy to swim around with a belt that might simply drop off by chance. Interesting logic there.
For years coroners and dive safety experts have wondered why divers have often been recovered dead from the bottom with air still in their tanks. A theory now being advanced by some is involuntary breath holding by conscious divers due to panic. This has important implications. It suggests a diver may simply breathold until he becomes unconscious and then loses his mouthpiece and it may also explain why some divers are found at autopsy to have lung expansion injuries. Through panic they may have held their breath while ascending either voluntarily or involuntarily as a result of swimming up and air in their BCD expanding and carrying them upwards.
If this is the case, and as yet it is unproven, then it emphasises the need for a diver who is beginning to get into difficulties to take effective measures to protect himself early on. As panic sets in it becomes harder to deal with the escalating situation rationally and there comes a point where the diver simply gives in to the panic and self rescue is no longer a possibility. One technique that I would offer up for discussion is to remove the weight belt and hold onto it. If the diver subsequently solves the problem he can refit it. I used and taught this technique for years as a snorkeller where the greatest risk is shallow water blackout during the ascent which can easily result in the diver sinking back into the depths. If, however, things deteriorate, the diver can jettison the belt deliberately (a conscious decision to do so indicates the diver still has some control of himself and may well have sufficient control to exhale on the way up). If he should lapse into unconsciouses he will hopefully release the belt and float to the surface. A diver who deliberately initiates a buoyant ascent and remains in control can slow his ascent by flaring.
The risk of DCI will increase once the diver exceeds no decompression limits. Even if the diver is located by rescuers they are extremely unlikely to attempt to decompress an unconscious victim. They will simply bring the victim to the surface. So the risk of DCI may very well be lower if the victim initiates a buoyant ascent early on instead of waiting to be rescued.
More support comes from Cpl Bob Teather of the Royal Canadian Mounted Police. Teathers field is recovery of corpses from water---including divers like you and me. In his text book for public safety dive teams, Encyclopedia of Underwater Investigations, he comments:
"It is indeed unfortunate that such an inexpensive piece of equipment, through its misuse, has directly contributed to so many diving fatalities! Simply stated, divers and diving equipment manufacturers and instruction agencies go to great lengths to provide and explain the use of the well known quick release buckle. In spite of this it is almost never used."
The Health and Safety Executive (who regulate commercial diving operators in the UK including paid recreational diving instructors) commissioned a report on diving accidents that was published in 1997. Drawing on fatality statistics provided by the BSAC in the UK and DAN in the USA, Scuba Diving - A Quantitive Risk Assessment states: "for 286 reported diving fatalities, includes only 4 fatalities for which specific mention is made to the effect that the event sequence included successful jettisoning of the weight belt."
Ditching a weight belt may also establish positive buoyancy more quickly than inflating a BCD. Under ideal conditions most direct feeds take a few seconds to inflate a BCD. Low performance direct feeds and low performance regulators may slow inflation further as may a regulator freeflow or rapid breathing each of which increases demand to the regulator which may not meet it adequately. Australian researchers found that it can take over one minute to fully inflate a BCD of 18 l capacity at 40 m. If the diver passes out before adequate lift has been established he will remain on the bottom. It may also be quicker to locate the weight belt buckle than find the direct feed which tends to swing around. Releasing a belt is also accomplished more quickly than depressing a direct feed button. For a diver who is about to lose consciousness or succumb to panic those seconds may be vital. Studies show that an unconscious diver exhales automatically during ascents and that even high speed ascents pose little risk of lung expansion injuries.
For the diver still concerned about fast ascents, it is possible to devise methods to slow things down. Weight systems can be used that divide the weight so that part or all of the ballast can be ditched. Weight integrated BCDs and harnesses usually permit half the lead to be ditched or in combination with a conventional weight belt a more precise balance can be reached. Provided enough weight is dropped a diver will become buoyant. It isn't essential by any means to drop it all.
In fact some divers do die after either getting into difficulties at the surface or reaching it, only to submerge and be lost. An overweighted diver entering the water with his air switched off for example would immediately start to descend and have nothing to breathe or, unless using a BCD with an emergency cylinder, anything to inflate his BCD with to return him to the surface. Dropping their weights might have assured their survival.
If you don't drop your weight belt you will almost certainly die. If you
do you might just live. 
Dive International