What Happens If You Run Out Of Air While Scuba Diving?

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What should you do if you run out of air underwater? Well in truth, running out of air when scuba diving shouldn’t be an option. Unfortunately this does sometimes happen, especially for new and inexperienced novice divers, but rarely for experienced divers. But what happens if you run out of air while scuba diving?

If you run out of air while scuba diving, you should turn to your dive buddy and use their alternate air source (or octopus air supply), buddy breath and ascend. If your buddy isn’t close enough for buddy breathing, your alternative is an emergency ascent, unless you have a redundant air source.

Pro diver tip: Never dive without a dive buddy, and only ever dive with a dive buddy who has an alternate air supply (octopus).

What happens if you run out of air while scuba diving

Running out of air while scuba diving used to be quite a common occurrence, and seemed to mostly happen with PADI novice divers. But this doesn’t appear to happen much any more, which is obviously a good thing.

Towards the end of this article, I discuss two real out of air situations that happened to buddies I was diving with. These real life out of air situations will I hope will be of interest to you, and about how the situations were dealt with and what the outcome was in each case.

Pro diver tip: If you receive good training with the right diving organisation, you will learn the skills needed to never worry about running out of air while scuba diving.

What to do if you run out of air scuba diving

You may now be wondering; what does a diver do if they run out of air underwater? Which is a very good question, with these 5 alternatives:

  1. Buddy air sharing followed by a safe ascent.
  2. Redundant air source followed by a safe ascent.
  3. Normal buoyancy ascent as you’re not actual out of air.
  4. Emergency swimming ascent.
  5. Emergency buoyant ascent.

It is important to note; in every case of an “out of air situation“, you should abort the dive and ascend immediately. You must not and should not continue with the dive, even in the case of buddy air-sharing.

1. Buddy air sharing followed by a safe ascent

You should only dive with a buddy who has an alternate air source. You should also stay close enough together that should a problem arise, you can reach your buddy in an emergency and use their alternate air source, or octopus air supply.

Close enough doesn’t mean you should be right on top of each other underwater, but it does mean you should be within a few fin strokes of reaching each other, just in case of an emergency.

It is important to carry out a buddy check prior to any dive, and most importantly, if you’re diving with someone you’ve never dived with before, a buddy check is all the more important. This gives you both the opportunity to learn how each other’s kit works and where kit is located, like their alternate air source in the event it is needed in an out of air situation.

What I tend to say to my dive buddy when I run through my kit during a buddy check, and after showing them where my octopus or alternate air source is located, is that they should simply take my alternate regulator from its clip without asking. This is quicker and safer in my opinion.

Once you’ve taken a few breaths from your buddy’s octopus and calmed down, as I guarantee you will be in a panic if you’ve run out of air scuba diving, is to start a safe ascent. If you are a part of a larger group of divers, and if possible, you should let at least one of the others know you are heading to the surface.

Diving with an alternate air source (octopus) is something that all scuba divers should do. I suggest that you should not dive with another diver if they don’t have one (see below what can happen when you run out of air underwater!).

For most recreational divers, their dive buddy is their redundant air source. But you can also buy a redundant air source as added safety equipment, and in the next tip, this is about protecting against the risks of running out of air underwater by having a redundant air source.

2. Redundant air source followed by a safe ascent

But not many recreational divers dive using a redundant air source. A redundant air source is a completely independent air source, sometimes referred to as a pony cylinder or spare air. This is separate from your main dive tank and regulator (or rebreather), which means you’ll be carrying another cylinder, which has its own first stage and second stage regulator set connected to it.

Having a redundant air sources is good added safety equipment if you regularly dive deeper than 40 metres and if you are taking part in decompression stop dives.

It is important to note that a redundant air source should not be used as an additional air source for the purpose of extending your dive time. The redundant air source is for emergencies only.

If your main air source runs out, which can be an open circuit system or a rebreather (closed circuit system), and if you have a redundant air source you start to use underwater, you should ascend to the surface immediately using a safe ascent. It is important to let your buddy know before you ascend to the surface, and they should accompany you to the surface for safety reasons.

3. Normal buoyancy ascent as you’re not actual out of air

If you think you’re out of air underwater and before you begin to panic, you may not actually be out of air but low on air instead. This can in theory happen if the ambient or surrounding pressure is equal to the pressure inside your scuba tank.

If you are finding it difficult to breathe from your regulator, check your air contents gauge first. It may be that your air is low, and instead of being out of air altogether, you may have enough to get you to the surface.

If this is the case, by ascending a few metres or feet, the surrounding ambient pressure will reduce, which will make it easier to breathe from your regulator. Make sure your buddy knows you are having a problem, and they should accompany you to the surface.

If necessary, and if your air does run out on your way to the surface, use your buddy’s alternate air source instead.

If you are not near to your buddy, and if you feel you don’t have time to swim to them, ascend immediately. If it looks like your air is going to run out on your way to the surface, you may need to switch to an emergency swimming ascent.

4. Emergency swimming ascent

An emergency swimming ascent is where you ascend much faster than you would ordinally do so.

An emergency swimming is an ascent where you use your fins to fin yourself to the surface vs using a normal safe ascent. With a normal safe ascent you will allow your buoyancy to bring you to the surface, which is normally controlled with the expanding air in your buoyancy control device as you ascend.

It is important to note that you must remember to breathe on your way to the surface (which is possibly the most important rule in scuba diving), as you don’t want to suffer the consequences of what might happen if you hold your breath underwater.

Emergency buoyant ascent

The difference between an emergency swimming ascent and an emergency buoyant ascent is that when you use an emergency buoyancy ascent, you will probably need to dump your weight belt to assist the fast ascent.

Important note about fast ascents is the increased risk of decompression sickness. Fast ascents don’t allow for the nitrogen absorbed into your body to off-gas slowly as you ascend, which may result in air bubbles forming in your tissues. This may lead to decompression sickness and could be fatal.

However, having said that, if you have no alternative than an emergency ascent, which carries the risk of decompression sickness, if you don’t ascend if you run out of air underwater, you are going to die in any event. So you may as well ascend and get to a bariatric chamber as fast as possible.

What happens if you run out of air while scuba diving and your buddy has no alternate air source?

If your dive buddy has no alternate air source, you will need to share the one regulator between you. This is something I trained to do when I first trained to be a scuba diver with BSAC, as alternate air sources were not an option at the time. Okay so I’m old and trained a long time ago, I get it. But this does mean I have a lot of experience too.

Sharing the one regulator requires each diver to take two breaths and pass the regulator to their buddy, who also take two breaths and then pass the regulator back, and so on. At the same time as sharing air with the one regulator, you should be carrying out a save ascent.

Lesson learned if you run out of air scuba diving

If you have run out of air scuba diving, this will be a lesson learned. Mistakes happen, but in this case it’s better that you don’t run out of air underwater in the first place.

To avoid running out of air, make sure you check your air contents gauge at regular intervals on the dive. The deeper the dive, the more air you consume in a shorter space of time, which means you should check your regulator more often the deeper you dive.

Real out of air situations

Sharing my personal experience: I’ve carried two diver rescues in my time scuba diving, both of which involved air-problems underwater. Neither of these out of air situations was because the person ran out of air as such, but a fault developed with their air supply.

Real out of air situations:

  1. Blown first stage diving in the UK: The first rescue involved a burst first stage hose. My buddy’s first stage blew, which meant his air supply was severely compromised. His air supply quickly diminished, and before it had completely run out, I was there to his rescue with my alternate air source. This meant I could turn off his air supply to stop the air escape and huge amount of air bubbles, but more importantly, it meant we could safely ascend to the surface using my air. This diving incident happened at around 15-20 metres (49-66 feet) in UK waters off from Torquay in Devon.
  2. Faulty air supply diving in Bonaire: I was asked by a French diver in Bonaire if he could join my buddy and I on a dive, as he didn’t have a dive buddy. Of course I said yes, so we went diving. At around 20 minutes into the dive, our new French dive buddy seemed to be indicating he was out of air. Being the dive leader, as my other buddy was a relatively novice diver, I went to his rescue. I gave him my alternate air source (or octopus regulator), and we made a safe ascent to the surface from around 20 metres (66 feet).

In the above out of air situations, they both ended well. But the reason this was the case is down to my own personal diver training, which kicked in automatically, because I was vigilant with my dive buddies, and because I was within a few fin strokes of my dive buddy too.

If you are new to scuba diving, and just building up your diving experience, you should book yourself onto a diving liveaboard. Diving liveaboards offer the opportunity to significantly increase your number of dives and experience, as spending time on a dive liveaboard is all about diving, where you can dive up to 3-4 times each day. Over a week, this can amount to 20 or more additional dives under your belt.

Please use the following table to find a suitable location and diving liveaboard:

I hope you enjoyed this page about what happens if you run out of air while scuba diving

If you have more questions either about snorkelling or scuba diving (or specifically about what happens if you run out of air while scuba diving), please comment below with your questions.

Please share your experiences, plus dive sites, resorts and liveaboards you recommend. Share the time of year of your trip together with what you saw, the visibility, currents and dive operator, as this will help others who read this page.

There will also be many more pages and articles about scuba and scuba diving safety tips (and on snorkelling too) for you to read and learn about this fabulous sport.

Have fun and be safe!

What Happens If You Run Out Of Air While Scuba Diving?

Article written by Russell Bowyer who has been a scuba diver since diving on the Great Barrier Reef in Australia in 1989. After his first dive he trained as a BSAC diver in the UK. He attained his Diver Leader certification with BSAC. He then went on to become a scuba diving instructor, teaching others how to dive and was voted as Diving Officer and Treasurer for the Saffron Walden BSAC club too. Russell has dived all over the world, including the UK, on liveaboards in the Red Sea, the Caribbean, South Africa and the USA. Russell is experienced in all dive types, including drift diving, deep dives that involved decompression stops and recreational dives too.

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