Using an underwater slate, record your depth and tank pressure.Establish neutral buoyancy at a fixed depth.Then you can complete the following steps: You can do this by first letting your dive buddy know what you are going to do and when (the beginning of a dive is usually the safest time to complete this exercise), and making sure you have plenty of air in your tank. Your SAC rate is calculated by measuring how much air (in this example we will use the metric system) that you use at a fixed depth for a fixed period of time. We don’t usually use our stress SAC rate to calculate for the average dive, however it is useful to have an idea of how much air you might use in a panic situation, to give you the knowledge of what is possible so that you stay well within your planned limits. Knowing your buddy’s SAC rate is also vital in the planning process, as although we always carry enough breathing gases in case of failures, we might also need to donate our reserves to a member of our dive team. We use the SAC rates together with the dive plan to calculate – as accurately as possible – how many litres of breathing gas we will use on that dive, which is a crucial aspect of planning any technical dive. Knowing your SAC rate is essential for gas management and dive planning, especially in decompression, cave and wreck diving, where we may not have direct access to the surface should we run low on air supply. Stress SAC rate – when hyperventilating, usually due to an emergency or overexertion.Resting SAC rate – when completing a stationary safety stop or deco stop.Working SAC rate – when moving from one place to another.Many divers refer to only one general SAC rate, but since we know that your air consumption will fluctuate during the course of a dive, in technical diving we often refer to three types of SAC rates that can be identified, which describe the three different levels of air consumption: The way we measure how much gas – usually air or nitrox, but for the purposes of simplicity we’ll just call it “air” – we breathe whilst scuba diving is called our SAC rate (surface air consumption rate) or sometimes RMV (respiratory minute volume). Today I’m going to explain why this idea breeds bad divers and can potentially cause dangerous behaviour.įirst of all, let’s discuss what we mean by “use less air”… What is SAC Rate / RMV and Why Should We Know It? I’ve witnessed – as I’m sure you have, too – many divers bragging about how much air they have left in their tanks after the dive and some even ridiculing other divers for having less. Arguably the biggest misconception in scuba diving is the notion that the less you breathe, the better diver you are.
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