It's easy to make one, and it's not really that dangerous if you're not careless, however most people are. But it's a short lived trick, and beyond that not safe to take anywhere. No one is going to let you troop in gear that could cause others serious harm. Even when using flammable, but not explosive material, there is still a possibility that something can catch fire, burn, melt etc. and to a basic costumer it's not worth a risk.
Go with the squirt gun idea if you want it to fire
-=QuinN!