Propane is available in both liquid and gas forms and both forms are combustible. If not handled properly fire or explosion can occur. Never smoke or have an open flame near a propane tank when it is being filled. Some gas will escape when the hose is being attached and removed from the tank for filling. Open flames near the tank during this time can cause combustion.
Because propane expands, care must be taken to not overfill the tank. If you overfill a tank and the propane expands, the tank can explode. For this reason, tanks are required to have OPV valves that will prevent overfilling.
The propane delivery truck should always be parked in a position where the driver can see both the truck and the tank being filled. Delivery drivers are equipped with a remote shutoff for their trucks. If there is a safety issue when filling the propane tank, the driver can remotely shut off the truck and stop the flow of propane.