Is Freediving Safe? What to Know Before Your First Course

Freediving has a dramatic reputation built on a handful of extreme stories that have little to do with a course. The honest answer to whether it is safe has two parts, and most articles only give you the first.

The first part: within a course, at the depths a beginner actually dives, this is one of the calmer things you can do in the water. Serious incidents come down to diving alone or going far past your training, and a course removes both.

The second part is the one usually left out. The research behind freediving safety is thin. There is no randomised trial, no meta-analysis, and no study that follows recreational freedivers with a proper denominator. Anyone who quotes you a confident accident rate is quoting something that has not been measured.

That matters more than it sounds, so this article says where every number comes from and how many people it involved.

What the research actually covers, and what it does not

Two things distort almost everything published about freediving risk.

The hard numbers come from competitions. In the largest field study, of 44 competitive freedivers across 143 dives, discipline averages ran from 54.7 to 71.7 metres; a second study at an AIDA world championship averaged 76 metres, with individual dives past 120. Lung loading increases with depth, so those figures do not transfer to someone working towards 20 or 30 metres on a course.

The numbers on pulmonary oedema come from surface swimmers. The only systematic review on the subject excluded freedivers on purpose, because the mechanism runs differently.

The field itself acknowledges the mess. In 2023 it introduced the umbrella term FIPS, freediving-induced pulmonary syndrome, precisely because squeeze, oedema and aspiration cannot be reliably separated in the data we have. The heaviest findings below rest on groups of 1, 2, 7, 10, 14, 30 and 44 people, and several sources are conference abstracts or consensus papers that were never peer reviewed.

That does not mean freediving is dangerous. It means the confident numbers you find elsewhere, including the reassuring ones, do not have much behind them.

The rule that does the most work: never dive alone

Every freedive is done with a buddy. One person dives, the other watches from the surface, ready to help, and you swap.

This is standard teaching across every agency rather than a measured finding, and the reasoning is simple enough to check yourself. Someone who loses consciousness at the surface with nobody beside them has no way back. Someone with a trained buddy is brought up and recovers. The rule is not a formality, and it is why trained freedivers are strict about it in a way that can look excessive from the outside.

Blackout, the risk courses take most seriously

A blackout is a brief loss of consciousness from low oxygen, usually near the surface at the end of a dive. It sounds like the worst thing on the list and it is the thing courses drill hardest.

Here is the honest state of the evidence: there is no reliable figure for how often blackouts happen to recreational freedivers, because the studies that would produce one have not been done. What a course gives you is prevention and management. Conservative limits, a proper breathe-up, recovery breathing, recognising the signs in yourself and in your buddy, and a buddy who is watching at the moment it would matter.

Your lungs at depth: what squeeze actually looks like in the numbers

This is where the measurements are best, and they are more reassuring than the word “squeeze” suggests.

In that study of 44 divers, 26 of 89 follow-up surveys (29 percent) reported respiratory symptoms and 17 (19 percent) asked for oxygen. But only 4 of the 143 dives met the strict definition of a squeeze, which is coughing blood together with a blood oxygen saturation of 95 percent or lower. A separate field study at a world championship found 15 of 50 dives (30 percent) symptomatic. Complaints at those depths are common. Actual squeeze is much rarer.

Depth is the best-supported risk factor and the relationship is still only moderate. Signs of fluid in the lungs appeared between 41 and 75 metres, while a separate study at around 10 metres found no change in lung function tests. Those are different studies measuring different things, so read the pair as a direction rather than a threshold. And at one world championship with 57 participants and 35 adverse events, there was no relationship at all between symptoms and depth.

Two findings are worth carrying into your own diving. Symptoms predict severity poorly: no single test worked well, low saturation alone was 52 percent sensitive, and of the four documented squeezes, two showed no B-lines on the lung ultrasound at all. Four cases is almost no precision, which is itself the point. So after a hard dive, do not rely on one signal, and certainly not on “there was no blood”. Recovery is quick but not immediate: the share of divers with lung ultrasound changes went from 17 percent before diving to 56 percent after, and dropped back to 33 percent within an hour, which is still around double where it started.

For repeated diving at more ordinary depths the picture is calm. Among 30 competitive spearfishers diving repeatedly between 12 and 45 metres across two five-hour competitions, 3 developed changes.

You will also hear that packing, forcing extra air into the lungs before a dive, adds to the risk. A 2023 systematic review raises it as a possible route to arterial gas embolism, and an earlier study did produce brief neurological symptoms after packing, both dry and in water. What does not exist is any figure linking packing to squeeze, or any effect size at all.

Pool sessions are not free for your lungs

This one surprised us, and it is relevant because our introduction is a pool session and we describe it as the gentle way to start.

In a group of 42 divers, lung ultrasound changes increased significantly after a deep dive to 50 metres. They also increased after maximal static apnea and after dynamic apnea in a pool, with no significant difference between those conditions. The pool is easier in every other respect, calmer, warmer, shallower, closer to help. It is not a place where your lungs are exempt.

Being fit does not protect you, and warm water is not a free pass

Immersion pulmonary oedema is fluid building up in the lungs during immersion, and the findings here run against intuition.

Of ten people shown to be sensitive to it, one was on blood pressure medication, all ten had normal blood pressure, and seven of the ten were described as extremely fit, training five to six hours a week: triathletes, a marathon runner, someone training for the decathlon. Be careful how far you take that. Those ten volunteered for an invasive heart catheter study, so the group cannot show that fitness fails to protect across a population. What it does show is that being very fit is no exemption. The mechanism looks like a pressure problem. Cycling underwater, sensitive people reached a pulmonary artery pressure of 34 mmHg against 22.5 in others at the same cardiac output, which is the same shift of blood into the chest that freedivers call blood shift.

Cold water is not a precondition either. The largest cluster of cases occurred at 23 degrees. We teach in water around 26 degrees and that is a real comfort advantage, but it is not a safety guarantee, and we would rather say so than sell you the warmth as protection.

There is no figure for how often this happens to apnea divers. Everything comes from swimmers, and those rates differ by more than a thousandfold between studies.

Drinking before a dive: the thing nobody measured

You will hear that you should drink plenty before a deep dive. It is one of the most repeated pieces of advice in the sport, and it has never been tested.

A review covering 166 freediving studies published between 2005 and 2025 contains no analysis of hydration. Not one. A separate review of apnea training does not mention it either.

What is on paper points the other way. Both dive medicine consensus documents, SPUMS/UKDMC 2024 and UHMS 2023, name drinking too much beforehand as a risk factor for pulmonary oedema and advise avoiding pre-dive overhydration in as many words. Neither advises extra fluid. The reasoning is that immersion already pushes blood towards the chest, so raising your cardiac filling before you get in starts you at a disadvantage. The strongest single signal comes from swimmers: in the study with the highest number of cases, 8 of 30, participants had drunk roughly 5 litres before a 2.4 kilometre sea swim.

Be honest about that recommendation too. In both documents it rests on a single case report from 1995, that same reference also carries their warning about heavy exertion, and neither states an amount or a limit.

There is a counterweight worth knowing. The same 2024 position statement notes that people who turn up with immersion pulmonary oedema are usually not fluid overloaded, which is why diuretics are not a first-line treatment for it. Drinking less is not proven prevention either. The role of fluid in the mechanism is unresolved, and the honest position is that nobody has tested it in freedivers.

So: drink normally. Do not load up before a deep session. Do not start dehydrated either, because that is nobody’s advice. There is simply nothing supporting “a lot”.

If something does go wrong, there is no norm to follow

The 2023 dive medicine workshop formally concluded that there is too little data to grade severity, to write treatment guidelines, or to say when someone can dive again.

What divers themselves do is not a guideline: the median return to the same depth was 10 days, with a range from the same day to four years. The little imaging that exists points to full recovery within about three weeks and no demonstrated long-term damage. That comes from one case report, in which the diver was admitted and treated with corticosteroids and antibiotics, so it describes a treated course and not a natural one, plus an unpublished conference study of 14 divers with no results section. It is not much to lean on.

The practical consequence is that we have no protocol to copy out of a book, because the book does not exist. Resting after blood or lasting symptoms is defensible mostly because nothing supports going back sooner. Lasting symptoms belong with a dive doctor, not with a dive school.

The two consensus documents also disagree about diving after an episode of pulmonary oedema. SPUMS/UKDMC advises strongly against it but writes only about scuba. UHMS includes freediving and calls one episode a relative contraindication and repeated episodes a serious one. That disagreement is unresolved, which is another reason this is a doctor’s call.

Things people say that have never been studied

Descent speed, water temperature, the number of dives in a day, and having had a previous squeeze have never been analysed as risk factors in a freediving study. They are barely even recorded. Anyone telling you that two deep dives in a day raises your risk is reasoning plausibly without a number behind it. There is also no recurrence rate for freedivers after a first squeeze.

The advice may well be sensible. It has just never been tested, and we would rather say that than let it sound like a finding.

How we run courses at The Gate Freediving

These are the rules we teach by.

• Two students per instructor, never more. Someone always has eyes on you.
• An instructor in the water with you, not watching from a boat.
• The buddy system at every level. No solo diving, including in the pool.
• Depth is earned. There is no schedule to keep up with, and a session that stops early is a normal session.
• Warm, clear, current-free water. That is comfort, and comfort helps you relax, which is the skill this sport is built on. We do not present it as a safety margin.

Who should speak to a doctor first

Freediving is open to most healthy people. If you have a heart or lung condition, uncontrolled high blood pressure, epilepsy, or ear problems that stop you equalising, speak to a doctor before you start, ideally one with dive medicine experience. Pregnancy is a reason to wait. If you have ever had fluid in your lungs after being in the water, that is specifically a dive doctor’s question, given the disagreement between the consensus documents.

We describe what has been measured. We do not give medical advice, and we would rather have the conversation before you book than after.

The honest conclusion

Freediving within a course, with a buddy, at depths you have trained for, is a calm and controlled activity. That part we stand behind.

The rest of what you read about it, including the reassuring parts, rests on a research base far thinner than the confidence of the writing suggests. So when you read that freediving is safe, or that it is deadly, look at what is behind the sentence. Often it is a competition study at 60 metres, and sometimes it is nothing at all.

Where these numbers come from

Every figure above says in the sentence what it came from, because that is the part that survives when a paragraph gets quoted somewhere else. This list is here so you can check any of it yourself.

• The 166-study review, and the absence of any hydration analysis: Paganini et al., Advances in breath-hold diving research: a state-of-the-art review, European Journal of Applied Physiology, 2025. Read it
• The competition squeeze figures, the B-line prevalences and the poor predictive value of symptoms: Yu, Silva, Lussier & Lindholm, Wilderness & Environmental Medicine, 2024. Field study, 44 divers, 143 dives, 212 measurements. Read it
• The 30 percent symptomatic dives and the depth correlation: Patrician et al., Frontiers in Physiology, 2021. Field study at an AIDA world championship, 40 divers. Read it
• The world championship with no depth relationship: Fitz-Clarke, Undersea and Hyperbaric Medicine, 2006. 57 participants, 35 adverse events. Read it
• Pool apnea loading the lungs as much as depth: Lambrechts et al., European Journal of Applied Physiology, 2011. 42 people, before-and-after field study without a control group. Reported through the 2025 review above.
• The spearfishers: Boussuges et al., Scandinavian Journal of Medicine & Science in Sports, 2011. 30 spearfishers across two competitions.
• The ten people sensitive to pulmonary oedema, and the pressure figures: Moon et al., Swimming-Induced Pulmonary Edema, Circulation, 2016. Ten susceptible subjects against twenty controls, with heart catheters, cycling in 20 degree water. Read it
• The swimmer data, the 8 of 30, and the thousandfold spread in rates: Spencer, Dickinson & Forbes, Sports Medicine Open, 2018. Systematic review of nine studies, all in surface swimmers, freedivers deliberately excluded. Read it
• The advice against pre-dive overhydration, and the scuba-only scope: SPUMS and UKDMC joint position statement on immersion pulmonary oedema, 2024. Expert consensus, not peer reviewed. Read it
• The freediving-inclusive guidance and the contraindications: UHMS Diver Medical Screen Committee, Diving Medical Guidance to the Physician, 2023. Read it
• The FIPS term, and the finding that there is not enough data for standards: Barotrauma and SIPE in Freediving, workshop proceedings, San Diego, October 2023, published 2024. Expert consensus, no vote or Delphi process. Read it
• Packing and arterial gas embolism: Blogg, Tillmans & Lindholm, Diving and Hyperbaric Medicine, 2023. Read it
• The three-week recovery case: Wagner et al., Diving and Hyperbaric Medicine, 2025. One diver, treated with corticosteroids and antibiotics. Read it

Two things in this article have no citation on purpose. The long-term CT work on 14 divers with a squeeze history is a conference abstract without a results section, and we say so where we use it. The claim that most serious incidents come from diving alone or overreaching is what every agency teaches, and we could not find a study that measured it.

New to it? The gentlest way to start is an introduction session in our pool, and you can read what a course actually looks like before you commit.