Plan Your Dive; Dive Your Plan
Planning your dive based on air consumption is not difficult. One common method for doing so is the rule of thirds. This rule is applied by dividing your gas supply, minus a 500 PSI reserve, into thirds. The first third is used for the descent and exploration portion of the dive, and the second third is used for the ascent and return to the boat or shore. The final third is kept in reserve as a buffer for unexpected deviations from the plan — this ensures you’ll have enough gas to safely get your buddy to the surface, deal with a free-flowing regulator, fight an unexpected current or handle other issues that can arise underwater. By planning your dive with this final third of your tank kept in reserve you can add a level of conservatism to the dive, although you should still remember to consider factors such as current, work load and depth as they may require even more conservative planning.
Factors Influencing Consumption
Many factors can affect your air consumption during a dive, but chief among them are depth, weighting, work load and personal fitness. Keep in mind that your air consumption will increase the deeper you dive, the harder you work and the more equipment you carry. A weight check before a dive to remove excess weight can improve your air consumption dramatically. Diving in a horizontal orientation will also help by decreasing your drag in the water. Improving your personal fitness, limiting the amount of gear you carry and minimizing your work at depth can also improve your air consumption, but keep in mind that site conditions such as currents and wave action are out of your control and will increase your effort in the water.
Check Your Gauge
It may seem self-evident to experienced divers, but it is vital to constantly check your gauges throughout a dive. Monitoring your air, depth and dive time can give you an idea not only of your air consumption and when you might have to end a dive but also whether your equipment is functioning properly. A slow leak from a first stage O-ring, for example, might not be obvious on the surface, but you may be able to deduce its existence by noticing an abnormally high air consumption rate during the dive. It’s easy to get distracted and forget to check your gauges, particularly as a new diver or when experiencing a new and exciting site, so remind yourself to check these as frequently as possible. Whether you do so about every minute or every few kick cycles or keep a gauge in your hand as a reminder during a particularly challenging dive, find a way to monitor your air consumption regularly throughout the dive.
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