I'm sorry, the point I was trying to make is that a dive buddy is also responsible for his partner. If he drowned while diving, even during a night dive, he was essentially diving alone. My son and I have done many night dives. (Our favorites are Sea Tiger and mantas off the Big Island) We are never out of contact with each other and regularly check things like our computers, NITROX use, etc. It's just what you do when you dive. The ocean is big, dark, and dangerous. You mitigate risk by following procedures.