If you have a tank that is completely liquid filled, it will expand in the heat. Since it is filled, there is no place for the expansion to go and the pressure builds. The tank will then fail at its weak spot, normally a connection or valve. By leaving the tank with some unfilled space, the liquid expands into that space when it gets hot (the gas is normally more compressible). At least that is what I was told in chemistry lab many years ago.....
I think about it like a concrete road or sidewalk. You should design it with little gaps (sometimes filled with tar or blacktop) to let the concrete expand in the heat rather than buckle.
NO,NO......EACH TANK HAS HIGH PRESSURE VENT FOR SAFETY...........you may hear it venting in hot weather....that is why ALL PROPANE TANKS SHOULD BE STORED OUTSIDE IN THE OPEN AIR.......not in the house or cellar
LPG cylinders have a safety pressure relief built into the valve, or tank, to allow the pressure to be released in case the cylinder is involved in a fire. In a large fire, these relief valves are usually too small, and the containers will explode into a spectacular fireball, sending metal fragments all over the place.
Both butane and propane are heavier than air and will accumulate in low points and cellars. Severe and fatal building explosions have occurred due to gas accumulations in basements.
If you get a lung full of propane , find stairs NOW & invert yourself, lie down head low & feet going up the stairs looking down at the stairs , lock legs or have someone hold from slipping & breath slow , The propane will leave on it's higher in the lower part of your lungs.
This I have seen twice , coworker was short of breath & complained , in 5 mins all back to normal .
Propane heaver than air will just flow out.
Newer style LPG containers have special valves that contain an OPD– overfill protection device– in the valve to prevent overfilling of a cylinder. LPG containers can only be filled to 80%, to allow expansion of the liquid as the cylinder warms up.