Why should you never top off a propane cylinder?

• A. It voids the cylinder warranty
• B. Overfilling can cause propane to expand and vent, leading to leaks and fire risk
• C. It makes the cylinder harder to transport
• D. Propane leaks are not affected by fill level

Answer: (B)

Propane needs some empty space inside the cylinder to absorb changes in pressure as temperature changes. When the cylinder is heated, the liquid propane tends to vaporize and expand dramatically. If the cylinder is filled to the top, there’s no room for that vapor, so pressure climbs and propane can vent through the safety relief mechanism. This vented gas is flammable, creating a real fire or explosion risk if there are any ignition sources nearby. So never top off a cylinder; leave space for vapor and fill only to the recommended level to maintain that safe vapor space.