My deepest condolences to the young man's friends and family.
I lost my best spearing mate to swb nearly a year ago. He was a very experienced spearfisherman and freediver. He could routinely spear fish in 30m of water, and he was one of the best blokes you could meet. I wish I was there when the accident happened, I might have been able to save him.
You don't need to know the science to reduce your risk of swb. My advice is
1) Always dive with a buddy that is capable of diving to a reasonable depth. My mate died most likely because his buddy couldn't get him out of the 30m of water he had sunk down to.
2) Do not hyperventlate
3) Always have a few minutes at the surface between dives to reduce your CO2 levels in you blood
4) Never exhail before you reach the surface. The experts liken that to suicide.
5) If you are spearing large pelagics DO NOT fight them under water. Have a good teather system with a float and let the gun go. This really burns your O2 and pushes up your CO2 fast. This is most likely how my mate suffered a swb.
It's a dangerous sport so treat it with respect and enjoy it.
Matt.