What should a diver always verify before using a nitrox cylinder?

A diver should always verify the FO2 (Fraction of Oxygen) and the MOD (Maximum Operating Depth) listed on the contents tag before using a nitrox cylinder because this information is critical for ensuring safety during a dive. The FO2 indicates the concentration of oxygen in the gas mixture, which directly influences the risks of oxygen toxicity and determines the depth limits for safe diving, as indicated by the MOD. Understanding this information helps divers plan their dives appropriately, ensuring that they operate within safe limits based on the specific gas mixture they will be using.

While checking the weight of the cylinder, the color, or the manufacturing date may provide additional safety information or context, they do not directly affect the immediate safety and planning aspects related to the nitrox gas being used. Ensuring knowledge of the FO2 and MOD ensures that a diver can make informed decisions and reduce the risk of miscalculating dive profiles or exceeding safe depth limits for the mixture.