Air Consumption
We think it is intuitive that one of the most important factors in the duration of a dive is the amount of air we carry. However, other factors no less important condition the duration of the dive, among which, of course, the diver’s air consumption emerges.
Although the two factors mentioned are quite variable, we can, however, adopt values that allow us to make, with some approximation, some calculations about the amount of air consumed and the air that is left.
AIR WE BREATHE
It depends on several factors:
- Volume of lungs.
- Effort we exert.
- Water temperature.
- Depth to which we have evolved.
- State of mind.
- Physical state.
- Diving experience.
We can therefore say that on the lower side of the consumption scale we will have a female diver, diving restily, low depth and in warm waters. On the contrary, a male diver, of high physical complexion, moving rapidly, the great depth, poorly prepared physically and in a state of panic, is located at the opposite end.
The human being, on the surface and at rest, consumes about six liters of air per minute. When you get up and move slightly your consumption, you double your consumption, and if the movement is faster, your consumption will double again.
NORMALLY, IN DIVE CALCULATIONS, THE VALUE OF 25 LITERS/MINUTE FOR AVERAGE SURFACE AIR CONSUMPTION IS ADOPTED
Let’s now consider the depth in calculating air consumption. By varying the pressure quickly with the depth (for every 10m a bar varies), our air consumption increases rapidly when we descend.
| Surface | -10 m | -20 m | -30 m | -40 m |
|---|---|---|---|---|
| 20L/min | 40L/min | 60L/min | 80L/min | 100L/min |
| 25L/min | 50L/min | 75L/min | 100L/min | 125L/min |
| 30L/min | 60L/min | 190L/min | 120L/min | 150L/min |
EXAMPLE
Therefore, if we adopt as an average diver consumption on the surface the 25 L/min , and if we are diving at 27.5m depth , where the absolute pressure is 3.75bar , our need for air per minute will be:
Consumption = 25L/min x 3.75bar = 93.75L/min
This way, if we are planning to take a dive lasting 25 minutes, we can determine that the amount of air we will consume in that dive will be:
93.75L/min x 25min = 2343.75L