[trux]

Well, it is always better telling what exactly you are looking for. That's why Laminar asked all those details. Your answers were quite confusing, and therefore it took a while before we could advise better.

In medical experiments, diving reflex is often triggered by a simulated face immersion - i.e. wet cold cloth (may contain a bag of ice). Using a bowl with cold water is a possibility too, but you lose the main advantage - the relative safety of dry apnea. For that reason, you should also use the wet cloth in such way that it does not inhibit breathing in case you black out. The area around eyes is allegedly the most important for the diving reflex. You do not need to cover your nose and mouth (or let an opening for them).

Blackout alone is not too bad if it happens during dry training. Although there are certain risks at dry apnea too, the likelihood of a fatal accident during wet apnea is much higher than when training dry. For limiting the risks, you should train dry in a safe position to avoid injury in case of BO or loss of motor control, and to minimize the possibility of choking with your own tongue. There is also certain chance of heart arrest at really bad blackouts, but I think such cases are very rare. AFAIK, only cases of heart arrest during sleep apnea are known, and those people usually already had some serious cardiac problems anyway. Having someone close to survey you, or check you out regularly during the training is not a bad idea though, if you want to push really hard while minimizing the risks.