If there is a doubt about the O2 rating of a cylinder, what action should be taken before the next filling?

When there is uncertainty about the oxygen (O2) rating of a cylinder, the most prudent and safe action to take is to undergo O2 cleaning. This process ensures that the cylinder is free from contaminants that could pose a risk when filled with high concentrations of oxygen. Contaminants such as oils and greases can ignite in the presence of pure oxygen, making O2 cleaning a critical step for safety.

Proper O2 cleaning involves a thorough cleaning process that eliminates any substances that could potentially react dangerously with high-pressure oxygen. This is especially vital for cylinders meant to contain enriched air nitrox, as they are frequently utilized for diving purposes where very specific gas mixes are crucial for the diver's safety.

Engaging in O2 cleaning before the next filling not only enhances the safety of using the cylinder but also ensures compliance with recommended practices for handling high-pressure oxygen systems. Through this method, divers can confidently use their equipment without the fear of unexpected hazards related to oxygen toxicity or combustion. While consulting the manufacturer can provide guidance, and labeling may offer some caution, the most effective action to mitigate risk in this scenario is through O2 cleaning.