Can You Change a Scuba Tank Underwater?

Changing a scuba tank is a common task among scuba divers, but it is usually done on land. Due to drastic changes in pressure, scuba diving requires you to check your equipment thoroughly before and during your dive. If you discover a leak or a malfunctioning regulator before your dive, you should immediately replace the faulty equipment before entering the water. But, what if something happens under the water?

Yes you can. But it is something you should train to do beforehand. An underwater change can flood your first stage and contaminate your regulator. You will need to be on a stable bottom, and it’s best to have someone to help.

While divers have successfully changed tanks underwater, they are highly specialized divers with several years of experience. Although it’s possible, it’s can be dangerous to replace a tank underwater. And please never sit or lie on a reef if you have to do this.

Your pre-dive equipment check is an essential process that you should never omit. Most equipment problems that occur while you’re diving could’ve been remedied before you entered the water.

This article will examine why you should not attempt an underwater tank change and how the record holder (for the longest underwater dive) accomplished underwater changes without incident.

Why Shouldn’t You Change a Scuba Tank Underwater?

Scuba diving is the ideal way to explore a hidden underwater world. Underwater exploration can be a hazardous pursuit if you fail to check your equipment frequently. Leaks and malfunctions will occur on some dives, but in most situations, you should surface before attempting a repair or replacement.

The following list and descriptions describe why you shouldn’t change a tank underwater.

  • Limited time before your air expires
  • Without assistance, changing equipment is risky
  • Your first stage could become flooded
  • Water can enter the regulator
  • You can experience nitrogen narcosis

Limited Time for Air Tank Replacement

When you’re running low on air and need to change a tank, you should swim to the surface to switch tanks. On rare occasions, divers must change a tank underwater, but in recreational diving, changing a tank is unnecessary and hazardous.

An underwater tank change requires a high degree of skill and experience. Underwater welders and rescue personal have changed tanks underwater in extreme situations, but generally, all divers prefer to change their tanks on land.

You have a minimal amount of time to change a tank when you’re low on air. You cannot change a tank underwater as quickly as you can change one on land. The low light and colder temperatures inhibit your ability to change a tank expediently. You may have only a few minutes of air left in your old tank, and that’s not enough time to attach a new tank safely.

Rather than get into situations where a tank change is needed, consider carrying a small backup air supply in case you run low. It can also be used for breathing while you make a tank change if that is in your dive plan. This Spare Air kit on Amazon has been the most recognized and top recommended backup supply kit for years.

Click the image to read more on this kit from Amazon

Without Assistance, Changing a Tank is Dangerous

Although most divers prefer to have a crew or a divemaster present for assistance, some brave souls enjoy solo diving and only rely on their skills in case of an emergency. However, even veteran divers should have a supervisor to observe the dive in its entirety. 

In diving, there are too many things that can go wrong. Having an instructor or friend present is a crucial element of safe diving. If you become hung up on a coral reef or sunken equipment, your friend can jump to your rescue.

Sharks, stingrays, and other aggressive marine life are also a concern when you’re exploring deep waters. Equipment problems should be addressed on land, but in the rare scenario that your tank must be changed underwater, only an experienced diver should assist you in the process.

During a Tank Change, Your First Stage Can Become Flooded

The first stage of a diving apparatus provides the connection between the air from the cylinder and the diver’s breathable air. As the main component of the first stage, the regulator connects to the air cylinder. 

The regulator pulls in high-pressure air from the tank and converts it to intermediate pressure air before sending it to the diver’s second stage. The regulator has a filter that prevents contaminants from entering, but it is designed to be set up on land.

You have to disconnect the regulator to change the tank, and when you reconnect it, you’re likely to allow water into the first stage if you’re underwater. The first stage that takes in water will carry it to the diver’s second stage. In turn, the diver will inhale some water instead of merely breathable air.

If the first stage is contaminated, it should be cleaned and sanitized before the next dive.

Water Can Contaminate Your Regulator

The filter protects the regulator on land, but it cannot block water from entering during an underwater change.

Even if it’s only a small amount of water that enters the first stage, the regulator and corresponding hoses will carry the water into the second stage. Regulators are designed for gas transfer (not liquid transfer) and will become contaminated by salt or freshwater.

It’s essential to tighten the regulator firmly to the tank, and each corresponding hose that attaches to the second stage should also have a tight fit. Tightening the regulator underwater is no simple task. A loose fit can cause leaks, damage to the regulator, and possible water contamination.

After the dive, you must thoroughly clean all pieces of equipment.

Nitrogen Narcosis Can Result From an Underwater Change

Although it varies between divers, most divers can show symptoms of nitrogen narcosis when you descend below 98 feet (30 meters). If you’re diving in shallow water, the condition isn’t likely to affect you.

Nitrogen narcosis occurs when an increase in the pressure of nitrogen and oxygen in your blood begins to affect your central nervous system. This condition has a narcotic quality that can make the diver slower, drowsy, and confused.

Nitrogen narcosis decreases as you ascend and will wear off once you’ve recovered on land. However, the condition worsens when you descend deeper into the water. An underwater tank change is perilous if narcosis occurs because the diver can become disoriented during the process.

If the disorientation causes the diver to swim in the wrong direction, the result can be deadly.

How Does A Skilled Technical Diver Change Air Tanks Underwater?

Only an experienced diver with a highly trained crew should attempt an underwater tank change. In 2014, Allen Sherrod (nicknamed the “Grouper”) set the world record for the longest underwater dive at 51 hours, 4 minutes, and 28 seconds.

Changing Tanks Underwater is a Team Effort

This incredible feat was accomplished with two assistants who monitored Sherrod and helped him with the tank changes. To make the tank changes easier, Sherrod attached tanks to the side of his body rather than to his back. You can view a three-minute video of the amazing record below.

The Grouper learned a lot from his previous record-setting dives and eventually decided to use an advanced dry suit rather than a wet suit for his 2014 attempt. A heating element was added to provide a more comfortable experience while the diver braved the chilly, deep-water temperatures.

When one of his tanks ran low, Sherrod signaled his assistants to bring a fresh tank. Before his helper attached the tank, Sherrod disconnected the empty tank and switched over to the auxiliary tank on his side. While one assistant helps with the tank changes, the other helper monitors Sherrod’s performance and observes his mental and physical condition.

The Regulator Must Be Attached to the New Tank

The assistants used tanks that were already attached to the regulator and hoses. Contaminating the regulator was not an issue since they used a preassembled tank apparatus. Every time they changed Sherrod’s tank, they checked the tank’s pressure gauge to make sure it wasn’t leaking.

Once the new tank was attached to his side, he disconnected his hose from the auxiliary tank and reconnected his hose to the new tank. The video makes the tank exchange look easy, but it is not a technique that should be attempted by beginner divers.

Closing Remarks

Scuba diving is the perfect way to explore underwater environments. To ensure you will not encounter problems during the dive, check your equipment carefully before you enter the water. Now, grab your gear and prepare to explore the deep blue sea.


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Tim Conner, M.D.

Tim Conner, M.D. started boating in 1974. He has been involved in recreational boating continuously since then. Dr. Conner has been active in boating and watersports safety education for decades. He rode his first jet ski in 1997, and rejoined the personal watercraft arena in 2012 with a Sea-Doo GTX 155, followed by 2 supercharged SeaDoos. Scuba certification came in 1988, and he and the family have traveled the world snorkeling and scuba diving for decades. The family has recently taken up paddle boarding. Click the photo for a lot more.

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