![]() Return to top ▲ Air ConsumptionĪt the surface, the average breathing rate is 25L/min. Questions 2 - 4 in the exercises is about Boyle's Law. If you did, as you ascended, the air inside your body would expand and this could result in a burst lung. The balloons on the right hand side of the diagram also demonstrate why you should never hold your breath during an ascent. ![]() Technical divers, that use air supplied from the surface, have their air delivered at pressure (i.e. This is one of the reasons why you can't take a hose down with you and use it as a long snorkel. Therefore, you are breathing twice the amount of air at 10m, compared to the amount of air that you would be breathing at the surface. The reason is, you would struggle to breathe if it didn't. So why is this so important? Well, as you descend, your regulator delivers air to your mouth and lungs at ambient pressure (the pressure of the surroundings). The diagram below shows this and also highlights an important point, about expansion of air on ascent. At 20m depth, the volume inside the balloon would be a third. If you were to take a balloon underwater, the following would happen, when you reached 10m depth, the volume inside the balloon would have halved, because the pressure is double. So what does this mean? Basically, as the pressure increases, the volume of gas decreases and vice-versa. You may remember from your high school physics lessons, learning about Boyle's Law? Don't worry if you can't, it says: "For a fixed amount of an ideal gas, kept at a fixed temperature, pressure and volume are inversely proportional." 's_law Question 1 in the exercises is about calculating pressures. Before you calculate air consumption, you'll need to calculate the pressure. You may be wondering why I started off by telling you how to calculate the pressure underwater, when you wanted to know how to calculate air consumption? Well, I'll get to that shortly. ![]() So for example, if you were diving to a depth of 17m the calculation would be: For every 10m depth, the pressure increases by 1bar, therefore the pressure can be calculated using this straightforward equation: This is actually equivalent to 1.01325bar, but for our purposes 1bar is near enough. If we are at sea level, we say that the air pressure is 1 atmosphere. Return to top ▲ PressureĪs we dive below the surface of the water, the pressure increases. Table of measurements, units and abbreviationsĭon't worry if you forget a unit or abbreviation, you can always refer to this table. The table below summarises the units we will need: Measurement For brevity, we tend to abbreviate the units of measurement. Unfortunately, we're going to be dealing with lots of different measurements and this means that there are lots of different units. ![]()
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