What must be done to a cylinder that has been opened to the atmosphere before refilling?

Before refilling a cylinder that has been opened to the atmosphere, purging it of air or moisture is essential. This step is critical because the introduction of air or moisture can lead to the formation of harmful substances within the cylinder. Air can contain oxygen and other elements that, when combined with LP gas, could cause corrosion or combustion issues. Moisture can lead to the creation of hydrocarbon mixtures that are not safe for use and can also cause contamination.

Purging ensures that any contaminants that may have entered the cylinder are removed, providing a clean environment for the new gas. It is a necessary safety procedure to prevent potential hazards associated with the presence of air and moisture in the system. This practice aligns with safety regulations and best practices for the handling and dispensing of LP gas.