By Don Casey
Revised by BoatUS editors in April 2012
There is a tendency to think of gas as something that disperses into the air, but this is a dangerous mischaracterization when the gas is propane. Propane is heavier than air, so it flows downhill like water. If you have a propane leak inside your boat, the gas will accumulate in the bilge--a bomb waiting to be ignited.
You must never mount propane tanks inside your boat. If you want them off the deck, they must be in a vapor-tight locker. A safe propane locker is fully isolated from the boat's interior, opens only above deck, and has a drain at the bottom to let leaking gas escape over the side.
Of course, such a locker will only contain leaks at the tank. To protect yourself against fuel line and/or appliance leaks, turn the gas off at the tank when not cooking, and learn the habit of flipping the fuel shut-off while one burner is still burning to safely empty the supply line. Every boat with propane aboard should also have one or more gas detectors--called "sniffers"--mounted low in the boat.