What is the correct fill practice for propane cylinders?

• A. Do not fill beyond 80% of the cylinder's water capacity to allow for liquid expansion.
• B. Fill to 100%
• C. Fill 90%
• D. Fill 70%

Answer: (A)

Propane must always be filled with headspace to accommodate expansion and vapor formation as the temperature changes. Filling up to about 80% of the cylinder’s water capacity leaves enough room for the liquid to expand and for gas to form without creating dangerous high pressure inside the cylinder. If a cylinder were filled to 100%, there’d be little or no space for expansion, increasing the risk of overpressure, venting, or a rupture when the gas warms. The 80% guideline is the standard safety practice because it provides a reliable balance between usable gas and a safe buffer for temperature-related changes.