I was really surprised at how quickly they go out.A fishing boat went down nearshore in bad weather, an old guy taking his regular 3 am piss just happened to see them shoot their last flare out his bathroom window and phoned CG. Yeah, I keep a big waterproof box of expired extras.
I must remark that shooting one of those 12ga flare guns on a dark moonless ocean is extremely disappointing, cheap bottle rockets work better.
The flares produce a lot of hot slag that you don't want landing on your boat. The idea is to hold them over the side so the slag drops in to the water and on the boat, potentially starting a fire, or worse on your bare toes.I’m surprised no one has marketed a holder for the flares once lit because some spit more than others.