Activities The Great Outdoors How Long Does the Air in a Scuba Tank Last? How Many Minutes Can a Scuba Diver Stay Underwater With a Single Tank of Air? Share PINTEREST Email Print Easy Answer: Never Long Enough!. Getty Images The Great Outdoors Scuba Diving & Snorkeling Gear Skills Safety Hiking Climbing Skiing Snowboarding Surfing Paddling Fishing Sailing Learn More By Natalie Gibb Natalie Gibb owns a dive shop in Mexico and is a PADI-certified open water scuba instructor and TDI-certified full cave diving instructor. our editorial process Natalie Gibb Updated May 24, 2019 How long does a scuba tank last? Although the question is simple, the answer is complicated. Let's examine different scenarios. An Average Diver, at an Average Depth, With an Average Tank Based on personal experience, an average open-water certified diver using a standard aluminum 80-cubic-foot tank on a 40-foot dive will be able to stay down for about 45 to 60 minutes before surfacing with a safe reserve of air still in the tank. Three Factors That Determine How Long a Diver's Air Will Last 1. Tank VolumeOne of the most common tanks in recreational diving is the aluminum 80, which holds 80 cubic feet of air compressed to 3000 pounds per-square-inch (PSI). However, scuba tanks are available in different materials and sizes for a variety of applications. Divers who engage in very deep or long dives may prefer tanks with a greater internal volume. Petite divers who use very little air may choose to use smaller tanks for comfort. All other factors being equal, a tank that holds a higher volume of air will last longer underwater. 2. DepthAs a scuba diver descends, the pressure around him increases. This increase in pressure does not affect the air inside the diver's scuba tank because it is already compressed to a very high pressure and the scuba tank is a rigid container. However, the water pressure does compress the air that exits the tank and flows through the scuba diver's regulator hoses and second stages. For example, the quantity of air that fills 1 cubic foot of space at the surface will only fill ½ cubic foot of space at a depth of 33 feet due to the compression of water. Similiarly, a diver will consume twice the volume of air at 33 feet as he uses at the surface. In other words, the deeper a diver goes, the more quickly he will use up the air in his tank. 3. Air Consumption RateA diver's air consumption rate will determine how long the air in his tank will last compared to the average diver. A diver with large lung volume (tall or large people) will require more air than a petite or short person with a smaller lung volume, and will usually have a higher air consumption rate. A variety of factors affects an individual's air consumption rate, including stress, experience level, buoyancy control and the amount of exertion required for the dive. Relaxed, slow and deep breathing is usually the best way for a diver to reduce his air consumption rate. Air Supply Is Not Always the Limiting Factor In many cases, a diver must end his dive before reaching the limit of his air supply. Examples include reaching the no-decompression limit for a dive (in which case a diver may consider using enriched air nitrox) or ascending with a buddy who has reached the limits of his air supply. Dive plans and dive sites vary. Just because a diver has air left in his tank doesn't mean he should (or will even want to) stay underwater until it runs low. Conclusion In the end, several factors determine how long the air in a tank will last for a particular individual and a particular dive. This is the reason that the question is so difficult to answer. Predicting how long a tank will last underwater requires an understanding of the physics of water pressure, tank volumes and air consumption rates.