Some technical facts
When fishing with explosives the massive pressure wave in the water causes the fish to get unconsious. It ruptures their swimbladder and they float to the surface. Some sink to the bottom. Fishermen then enter the water and scoop up the dead fish. Fishing with explosives kills everything instantly because the shockwave travels extremely fast in water ( up to 10000 meters per second) The fact that the 3rd man was found unconsious tells me the fisherman were at or near the scene. The fact that they also found the two other victims also is an indicator that they were equiped to salvage objects under water.
Some other facts
The velocity of detonation of high explosives is about 5,000 to 10,000 m/s, and a shock wave that propagates in all directions is produced in the water. The main features of the shock wave from 1000 gram TNT ( a common explosive) fired under water are:
The Force inside the explosion is 274 dB in 0,1 second or 250000000 megajoule.
One megajoule (MJ) is equal to one million joules, or approximately the kinetic energy of a 1000 kg vehicle moving at 160 km/h (100 mph).
This force is so high and short it instantly kills everything within considerable distance to the blast.
The safe distance a diver needs to follow for a 11 kg explosive devise placed in 27 meter deep water is 320 meter on surface, 1460 meters at a depth of 7,6 meter and 2320 meters at a depth of 23 meter!
(source
http://dspace.dsto.defence.gov.au/dspace/bitstream/1947/3763/1/DSTO-GD-0080 PR.pdf)
The depth of the divers makes an enormous diiference. This is the reason why the fisherman on the surface can be relativey safe close to the explosion but for divers it's very dangerous.
This could be the reason why the third diver survived the blast, if he was relatively close to the surface
The dive computer could answer a lot of questions.
It is very important for the family to know that the victim never even realised something happend. It takes about 100 ms for a sensory stimulus to travel to the brain and 160 ms for the brain to process the stimulus.
The blast was travelling at 1,5km/second underwater so the victims never felt any pain, and they were killed or stunned unconscious instantly without any pain.
I hope this will help the family in finding some peace of mind. To the sister your brother never felt any pain and his brain never even registered the explosion. A sad accident, but a comfort to know that your brother died while doing something beautifull and he passed away without him knowing or feeling it.
The fishermen on scene are IMHO the prime suspects in this case. Other fishermen stay far away from fishermen who fish with explosives because it's very dangerous and highly illegal. These explosives frequently cause a 2 meter wide hole in the coral and because water conducts the explosive force better then air the blast is extremely dangerous for anything in the water.
A "diver below" buoy could have prevented this accident.
I would also go to Viëtnam and visit the scene of the accident. Ask if the consul or a diplomat can escort you. Countries like Viëtnam with a developing diving tourism fear the presence and interest of international press and they otherwise might try to sweep it under the carpet . Visit the local Viëtnamese state representative with a delegation and maybe invite the international press. This will safeguard a thorough judicial investigation and a fast repatriation of the remains.
This way the death of these divers could contribute to stopping dynamite fishing in Viëtnam and enhance diver's safety in Viëtnam.
