What Do You Do if You Run Out of Air When Scuba Diving?

What Do You Do if You Run Out of Air When Scuba Diving?

If you run out of air when scuba diving, if possible, signal your dive buddy to share air and safely ascend to the surface after doing a safety stop whilst using their alternate air source. If you are in a ‘sticky situation’ and have run out of air, and they are unable to assist you, you will need to perform a “Controlled Emergency Swimming Ascent”, also known as “CESA“. Keep your regulator in your mouth and exhale and ascend without a safety stop at a rate no faster than 18 m per minute.

There you are – completely immersed in your underwater environment, following your dive guide slowly around the dive site.

Every few minutes, you look around at the colourful fish surrounding you to spot your dive buddy, and you give each other the easily recognizable ‘OK’ hand signal and continue on with your dive.

A few minutes later you start to feel a tug in your throat like it’s getting harder to take in air, and you look down at your submersible pressure gauge (SPG) and see the needles position, and the realization hits you – I am out of air!

It’s something that shouldn’t happen, especially in a sport that values safety as an absolute priority.

Scuba divers undergo repetitive training when we learn to dive or when we undergo a refresher if it’s been a long time since your last dive to ensure this scenario doesn’t happen.

If you have paid for fun dives and to be taken around some dive sites – there is some responsibility on the guide to check you – but untimely you are responsible for managing your air supply.

So what do you do if you run out of air?

The very first thing you should do is breathe very slowly to try and conserve your remaining air and then find your buddy (or another diver close by) and swim right up to them, right in front of their face, grab their BCD and if you need to get their immediate attention  – give them a good shake. Once you make eye contact, your training should kick in, and you make the hand signal for “out of air”, your buddy should then raise their left arm, so you can reach out and take their alternate air source (octopus regulator) and begin breathing again.

This is a very short explanation of what you need to do and what other measures you can take, but in essence – you need to find a supply of air and then ascend to the surface after performing a safety stop.

If you can’t reach your dive buddy or another diver, then you need to head slowly to the surface, breathing out your last breath just like you learnt in the “CESA skill”.

When you undertake your Open Water diving qualification with a recognized provider like PADI or SSI, you will spend quite a lot of time understanding the physics of how breathing underwater can affect your body and how to perform an emergency skill should you run out of air.

Imagine this, you have run out of air scuba diving, and you have no one to assist you, what should you do next?

If I Run Out of Air Scuba Diving, How Do I Ascend Safely?

If you do run out of air scuba diving, and you are unable to find assistance from your dive buddy then as mentioned, you will need to slowly ascend on one breath, performing an emergency controlled swimming ascent, which we will go into more detail later in this article!

It is important to note, that you can’t just kick like mad to the surface from any depth under around 7m as the pressure of the water has increased the pressure of the air coming out of your tank as you breathe, which in turn increases the number of molecules you take in with each breath.

This has increased the number of molecules in your lungs – the deeper you are, the more there is.

As the increased air molecules will expand in your lungs when you rapidly swim to the surface, you could end up with a lung expansion injury, or you could end up with decompression sickness (DCS), also known as “the bends”.

Scuba diving accidents such as these are hammered home during the beginner course to ensure you understand the dangers and to stop you from ever kicking as fast as you can to the surface.

During the Open Water Diver Course, you will learn about the dangers and accidents that can occur underwater, and skills you need to master to become certified, and more importantly, an independent diver.

This training is conducted in a swimming pool or a pool-like body of water. Your instructor will go over each skill, explain why they are needed and will demonstrate the skill before you complete them.

As explained above – the first thing that happens is you find your dive buddy and let them know you are out or air with a hand signal, they then raise the arm to allow you to grab their alternate air source, you then remove yours and immediately replace it with theirs and take a deep breath.

scuba hand signals out of air 1
Draw your hand horizontally across your neck; classic “dead” pose!

Next, you and your buddy then link forearms, give each other the ‘OK’ signal, and slowly ascend to the surface together. Once at the surface, you will need to inflate your Buoyancy Control Device (BCD) orally to remain positively buoyant at the surface, as you have no air left in your tank to inflate using the inflator hose.

But what if your buddy is not close enough and you do not have enough time? Well, now is the time to perform a CESA that you learnt back in your Open Water Course!

What Is a Controlled Emergency Swimming Ascent (CESA)?

A Controlled Emergency Swimming Ascent is used when a scuba diver runs out of air when diving. During the ascent, you will propel yourself towards the surface at a safe ascent rate, kicking using your fins, with continuous exhalation at a rate unlikely to cause a lung overexpansion injury. Remember scuba divers cannot surface quickly, so if you need to perform a CESA underwater, swim no faster than 18 m per minute.

Every scuba diver would have learnt the Controlled Emergency Swimming Ascent (CESA) during the Open Water Course training.

This is where you practice being too far away from your buddy or another diver for you to use their alternate air source, where you have no choice but to reach the surface alone.

This is practised by the diver taking their final breath or air, looking up at the surface and breathing out their last breath of air slowly as they swim to the surface making an audible ‘arrrrrrrrgggg’ sound.

It’s important to note that both in practice and real life, you still have to swim slowly at a rate no faster than 18 m per minute to reduce the chances of DCS or a lung overexpansion injury.

CESA is an important emergency management skill that allows you to safely reach the surface in the unlikely event of an out-of-air emergency. It is important to keep up to date with the CESA skill and all other emergency management skills.

CESA is practised many times in both the confined water and open water training with your instructor during the course. By the time you finish the course, these skill sets will have become close to second nature – as they should be, in order to save your life if you run out of air scuba diving.

If you are reading this, and you cannot remember how to perform the CESA skill, then maybe it is time for a refresher!

I Don’t Remember How to Perform a CESA…

If you have not been diving for a period of six months or more, its recommended (and a legal requirement in many countries) that you undergo a refresher course that is usually half a day or a day-long course, including a supervised dive to get your latent skills back up to speed.

Many people shun these refreshers and will head our diving after years between dives, buts it’s not a very smart thing to do. After all, these refreshers are designed to remind you of the skills that can save not only your life but also those diving around you.

During the refresher, the instructor will go through what to do if you run out of air when scuba diving.

But hang on a minute…it is important to also know how to prevent running out of air when scuba diving!

How to Prevent Running Out of Air When Scuba Diving

You can prevent running out of air when scuba diving by keeping an eye on your SPG during the dive, knowing your average air consumption, planning when you and your dive buddy should start shallowing up, and when you need to end your dive.

We plan dives beforehand and when we plan, we decide or determine how deep and for how long we are going to dive.

This used to be done with some tables and a bit of maths to work out what our limits are on time and depth, but these days with advances in technology we have dive computers. These allow us to plan and manage our dive times more effectively, and much more easily!

We should also know what our general air consumption rates are, some of us tend to use our air faster than others.

The more dives you do, the better you will understand how long it takes for you to use the air. The deeper we dive, the more air we consume, this is something every diver should be aware of.

Factors such as heavy seas and big swell, seasickness, ear issues taking longer to get down to your depth, strong currents and animal encounters can all cause us to breathe faster than we normally would and therefore run out of air faster than normal.

This of course is still all skills and planning that we undergo to ensure we dive safely, but nothing will suffice for simply checking SPG regularly underwater.

Dive Instructors and divemasters will generally check you once or twice through the dive, so they can see how fast you are going through your air. This allows them to plan the second part of the dive and know when the group needs to start swallowing up.

However, it’s really up to you to check you have enough air to last the dive or if you cut the dive short.

Most scuba tanks start with a pressure above 200 bar (3,000 psi) on the gauge and every gauge will have the figures turning to red when the needle comes down to 50 bar (750 psi).

This red section is a reminder that you don’t have long to go before you run out, and you should start ascending. At 50 bar, most people still have enough air to come up to 5 m, do a 3-min safety stop and surface without ever experiencing an out of air scenario.

Some dive guides might place the low on-air number at 70 bar instead of 50 just to be even safer and reduce the chances of a diver running out of air during the dive.

By constantly checking and re-checking your air supply, there should never really be a time that you do run out of air when scuba diving.

Scuba diving is one of those activities that can be quite dangerous, but as long as you follow your training and abide by some rules – chances are you will never have any issues at all.

If you do run out of air when scuba diving, would you be that diver to hold your breath in panic? Does that sound like you? If so, am going to tell you why it is SO important not to do this…

What Happens if You Stop Breathing While Diving?

Holding your breath when scuba diving is extremely dangerous – you could end up with partial or completely collapsed lungs. Remember that the most important rule of scuba diving is that you should never, ever hold your breath!

This is because, even though you may not realize it – holding a full lungful of air will make you buoyant, and you will begin to float upwards, which decreases the pressure in your lungs, which in turn expands the air molecules inside your lungs, which could cause a lung overexpansion injury – OUCH!

So, even when we practise any skill that requires us to take our regulator out of our mouths – we still ensure we continue to breathe out by displaying little bubbles from our lips.

With repetition and practice of skills and learning about the dangers of holding your breath underwater, you should never stop breathing when breathing compressed air under pressure like in diving.

Sometimes, we panic, trust me, I have been there too… Sometimes it feels like we are not receiving enough air through the regulator. So, let’s see why this happens!

What Should You Do When the Regulator Does Not Give Enough Air?

When we feel a sense of panic underwater, we naturally breathe faster and deeper. Sometimes it feels as if the regulator is not providing us with enough air underwater. Well, did you know that most regulators have a switch to control the flow of air you receive?

Diving regulators are designed to provide you air at different depths, and they do that automatically, however they do have a small switch that can increase or decrease the flow of air into your mouth and lungs.

Often though, the real problem, if a diver can’t seem to get enough air, is that they are breathing way too hard. This could be due to a current or waves, or nervousness of the diver.

If you ever do find yourself struggling to breathe from your regulator – the best thing you can do is to try and relax, swim with the current or hide behind a rock and calm down.

If you continue to struggle, it’s best to end the dive and ascend to the surface and potentially try a less challenging dive net time to build your confidence back up again before undertaking a dive at your confidence limit.

While we are on the topic of air, let’s see if divers can use 100% oxygen.

Can You Dive With 100% Oxygen?

Divers can dive with 100% oxygen, but only to a depth of 7 m, after that, it can actually become toxic to our bodies.

This has to do with partial pressures, the amount of oxygen we breathe (reducing down from 100% allows us to go deeper) and the way our bodies react to different elements and molecules under the water. It’s never wise to go diving with 100% oxygen, and this should only be used for an emergency response to a diving injury.

Sometimes 100% oxygen is used in very shallow diving operations and certain phases of mixed gas diving operations only.

If you wish to stay underwater longer and feel fresher after, you can use enriched air (NITROX). NITROX allows divers to stay underwater by reducing the nitrogen and increasing the oxygen content of the air in your tank. It is a really quick and easy certification to get too!

We have another article on this topic, that goes right into the science of what the different gasses we breathe do to our bodies at depth and at different percentages here if you would like to understand more about the fine details of why 100% oxygen is not used in recreational diving.

Don’t Forget Your Dive Insurance!

Before you go out on any dive trip or holiday, it is essential to make sure you have insurance that covers you if something goes wrong, like running out of air when scuba diving. Check out our dive insurance article for more information.

Or go straight to these dive insurance company websites:


Diver Alert Network (DAN)

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Summing Up!

Scuba diving is an extremely exciting sport that is not dangerous if you follow your training and always dive with a buddy, however, once, in your diving life, you may experience a situation where you run out of air scuba diving, or you may have to assist another diver underwater if they get into this ‘sticky situation’.

If you do run out of air when scuba diving, try not to panic. If your dive buddy is close enough, firstly signal them using the correct hand signal to “share air” and safely ascend to the surface after doing a safety stop whilst using their alternate air source.

If you both ran out of air and your dive buddy is unable to assist you, you will need to perform a Controlled Emergency Swimming Ascent (CESA). Remember to always keep your regulator in your mouth and exhale without a safety stop at a rate no faster than 18 m per minute when performing CESA.

But suffice to say, when we remember our training, check regularly and dive with a buddy, we should never have to encounter an out of air or hard to breathe scenario in our lives.

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Paul Fulbrook

Paul Fulbrook is a writer, scuba diver, ex-science teacher and marine biologist. He has a passion for coral reef biology, diving on coral reefs and writing about diving. He also loves cats and his children (sometimes).

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