Propane is stored in portable and detachable cylinders, such as those on your barbeque, or tanks, which are permanently affixed to a vehicle.
Cylinders are filled by weight and the pertinent information for each individual cylinder is stamped on the protective flange surrounding the valve. This information includes the empty weight of the cylinder (tare weight ) and the water capacity in pounds and allows the re-filling attendant to calculate the exact amount of propane to put into the cylinder. This is the approved method for filling cylinders in B.C.
Some cylinder valves are equipped with a bleed valve, that when opened, shows when the cylinder is filled to 80%. However, the present valve on the cylinder may not be the original valve and may or may not be the proper valve for that particular cylinder, possibly resulting in an over filled condition.
A motor home tank is filled by volume using the 80% bleed valve to indicate the proper fill level. All new tanks are equipped with an automatic valve that shuts off the propane flow at the 80% capacity level.
Any person dispensing propane in Canada, must, by law, be certified by the Propane Gas Association of Canada by successfully completing a training course in the safe handling of propane.
Also, by law, it is an offense to fill a propane cylinder or tank beyond 80% of it's capacity and that law is in place for a very good reason. Propane is stored in a liquid state by compressing it in a cylinder or tank. At 80% full there is the remaining 20% of the storage capacity to allow for expansion of the liquid due to temperature changes. If the tank is over filled this expansion room is decreased to the point that the built in pressure relief valve will vent off enough propane to avoid tank rupture. If the cylinder is lying on it's side when this happened it would vent off enough liquid propane to reduce the internal pressure to below the preset pressure of the relief valve. When liquid propane is released it will expand to 270 times it's volume. Propane is heavier that air and tends to collect at the lowest spot, such as the lowest deck of a ferry, where enough can be present to cause an explosion.
An LP gas inspection on a recreational vehicle should only be performed by a licensed RV class Propane Gas Fitter and you have every right to ask for qualifications.
In short, propane gas is a clean, efficient and convenient fuel source and very safe to use when all safety precautions are observed.
For more on propane cylinders, tanks and valves see: www.propane101.com/propanecylinders.htm