Don't know, every time I have used a flare I let it burn all the way out.
Something else I carry is a film canister of carbide. Carbide works great for those wet situations.
Someone already said it and it sounds like overkill but I also carry about 3-5 forms of fire building...
I like to carry:
1. Strike anywhere matches in waterproof container
2. Light My Fire fire starter
3. Lighter that is clear to see how much fuel is left
4. 9V battery and steel wool
5. Vaseline soaked cotton balls
6. Candles are good, you can buy a bag full of the small tub candles for pretty cheap
Just some things I like to carry that I can think of off the top of my head. I know there are other things that I have used and carry but can't think of them right now. I like to carry any combination of several things just to make sure...