All cylinders between 4 & 40 pounds much have OPD Valve. You can Identify these by their unique triangular handle.
Never Leave a filled propane tank in a hot car for extended periods of time.
Propane Boils at -44°F (-42°C)
Propane Gas is heavier than air
1 Gallon of Propane Weighs 4.3lbs
Propane is a hydrocarbon(C3H8), also known as Liquefied Petroleum Gas or LPG, is a gas normally compressed and stored as a liquid. It is nontoxic, colorless, and virtually odorless; an identifying odor (ethyl mercaptan) is added so it can be detected.
Propane is an approved, alternative clean fuel listed in the 1990 Clean Air Act and the National Energy Policy Act of 1992. Propane is also nontoxic, so it’s not harmful to soil or water.