It depends on a few crucial factors. Which makes it entirely inaccurate to answer how long does a scuba tank last with a definite answer like 20 or 30 minutes. Nonetheless, scuba pros will tell you that an 80-cubic-foot standard aluminum tank will last about 45-60 minutes before hitting reserve, on a 40-foot dive.
With those figures, you can estimate how long an oxygen tank will last on a 130 feet dive.
But before that estimate, here are the five vital factors that will affect the final figure:
1. Tank Volume
Source: How Long Will My Tank Last
Scuba tanks come in a variety of sizes. The aluminum 80-cubic-foot mentioned earlier is the most common of them all. It contains air, 80-cubic feet, compressed to 3000 PSI (pounds-per-square-inch).
For deep diving, it’s best to use such big tanks. The higher the internal volume, the more prolonged the cylinder will last underwater. However, the best scuba cylinder is the 12-liter one.
Remember, there are two kinds of scuba tanks: aluminum and steel. The type of container you own plus how well it’s maintained can also affect its oxygen holding capacity. The DOT (US Department of Transportation) regulates all scuba tanks, and each cylinder should undergo hydrostatic testing every five years.
2. Tank Pressure
Most diving cylinders get filled at 200 bar (3000 psi). There are others filled at 300 bar (4000 psi) or even more, but they’re rare. Always check a tank’s maximum working pressure because it determines how much oxygen it holds.
So how long does a scuba tank last in terms of pressure? You guessed it- The higher the psi, the more extended the dive.
Source: How long does a scuba tank last?
While scuba diving, the deeper you descend, the more pressure around you increases. The pressure increase doesn’t affect the air inside your tank. Because the air gets compressed at high pressure and the container is quite rigid.
However, water pressure compresses air exiting the tank and flowing your regulator horses, plus second stages. For example, it takes twice the amount of air required to fill one cubic foot of space (at the surface) to fill the same space at a water depth of 33 feet due to compression. That means that you will consume twice the amount of air at 33 feet compared to your intake at the surface.
Therefore, you can’t answer how long does a scuba tank last without considering that you will take in a lot of air at 130 feet.
4. Lung Capacity
Many things that differ from person to person. And one of them is lung capacity. Usually, bigger people have more lung capacity than small-size individuals. Meaning that if two different sized divers with the same breathing rate scuba dive, the smaller one will require less amount of oxygen to last as long as the bigger one.
Because the bigger person needs more air to fill his/ her lungs than the small guy. Still, lung capacity doesn’t have to matter if you improve your breathing rate to control air consumption. Thus, you can accurately judge a person’s lung capacity by size alone.
5. Breathing Rate
Source: Breathing Tips For Scuba Divers
While underwater, the more breaths you take (per minute), the faster your tank depletes. If you want your cylinder to last longer, you ought to breathe slower. And how do you do that?
Clear your dead-air space off carbon dioxide by exhaling longer. Contrary to popular belief. This carbon dioxide is what triggers the urge to breathe and not lacking oxygen.
Your body triggers the urge to breathe if the level of carbon dioxide in your lungs is high enough.
Nonetheless, other factors that affect your air consumption rate whether you exhale enough or not. They include buoyancy control, experience level, stress, and amount of exertion needed when diving. All in all, relaxed, deep and slow breathing will reduce your air consumption.
How long does a scuba tank last at 130 feet?
The simple answer is generally less than one hour.
Since an average scuba diving beginner, in calm water (80° degrees Fahrenheit), breathing normally, would take about an hour to empty an 80 cubic foot cylinder at 33 feet. It’s easy to double this time if you train yourself on the economy of motion, plus breathing/ buoyancy control.