How Long Does Air in a Scuba Tank Last?
Air Consumption: the Basics
Everyone has a different basic surface air consumption rate. This depends on gender (males have bigger lungs on average), fitness (those in good physical condition use less air), smoking (smokers use more air) and stress (the more stress the more air). On the surface, these differing air consumption rates really don't matter because the air that we are able to breathe is unlimited.
However, when you go underwater in scuba diving, your air is limited by the tank. This problem is compounded by the fact that when you go under water, the pressure increases, including the pressure of the air in your tank. For example, when you go to 10m underwater, you use the air in the tank twice as quickly as you would breathing from the same tank on the surface. At 40m, it's 5x more quickly. So things like gender, fitness and stress can really make a huge difference.
Air Consumption: Part 2
Now that we've covered the basics, there are a few more factors to consider about how long your scuba tank lasts when diving.
1. Water temperature: the colder the water, the faster you will use your air because you need a thicker wetsuit and more weights.
2. Weighting: the more body fat your have and the more inexperienced you are, the more weights you will need to use and the faster you will use your air.
3. Trim: if you have things dangling all over your body, it will be harder for you to move through the water and the faster you will use your air.
4. Current/work-load: if it's a very relaxing, easy dive, you will not use your air very quickly. If you are constantly kicking very hard, you will use your air rapidly.
5. Experienced level: the more experienced you are, the less air you will use.
6. Tank Size: an obvious one worth mentioning!
Did I miss any factors that influence air consumption?
Just Answer the Question Already!
How Long Does Air in a Scuba Tank Last?
It should be obvious by now that there really is no answer. I'm a diving instructor and will occasionally have twice as much air remaining in the tank as other divers at the end of the dive. Most often, I have 10-30% more.
As a general rule though, in tropical conditions you can expect your dives to be between 40-60 minutes, unless you're going very deep for some specific reason such as a shipwreck, in which case you'll use your air much more quickly. In colder waters, where 5-8mm wetsuits or drysuits are required, you can expect your dives to be between 25-40 minutes.
