[seafox]

Just as an example of what could have happened to the Thai spearfisherman and not to divert the investigation, but spearfisherman can get shallow water blackout and die from that.

Shallow water blackout can occur when a breathe hold diver(BHD) stays down too long. The body actually plays a trick on itself. The thing that makes you breathe is not a lack of oxygen but an excess of CO2, carbon dioxide. When a BHD goes underwater the air in his lungs is compressed. If he goes to 33'(10 meters) his lungs now have only 1/2 the volume that they did at the surface, while still having the same amount of air in them. As the CO2 level builds up in the body, there is no warning while the diver is at depth because the volume in his lungs is less than before. As the BHD goes to the surface the volume in his lungs increases(doubles from 33'(10 meters) to the surface and so does the CO2 level. If the BHD has stayed down too long, he will start feeling the need to breathe but if he is underwater he will not be able to. If the CO2 level gets too high, the body will protect itself by shutting down motor functions to save the brain and major organs, meaning that his arms and legs will stop propelling him to the surface. The BHD will pass out and if he is underwater when this happens and no one is around he will die unless he ends up face up on the surface, and even then he still has to start breathing again while unconscious.