Freediving Safety Rules

Freediving is safe. More precisely: freediving with trained buddies following established safety protocols is safe. Freediving alone, or with untrained companions ignoring the rules, is genuinely dangerous.

The rules in this guide exist because people died before they were understood. They are not bureaucratic caution — they are knowledge purchased at real cost. Follow them every time. There are no exceptions worth making.

Never Freedive Alone — The Absolute Rule

This is the foundational rule of freediving safety. It has no qualifications and no exceptions:

Never freedive alone. Not in the ocean. Not in a pool. Not even in shallow water.

The reason is shallow water blackout — explained in detail in the next section. The short version is that a freediver can lose consciousness with no warning, at any depth, in any conditions. An unconscious person face-down in water drowns within minutes. A buddy on the surface watching the diver is the only reliable prevention.

The rule applies equally to:

• Static apnea (breath holding while floating)
• Dynamic apnea in a pool
• Ocean or bay diving at any depth
• Snorkeling alone (drowning from shallow water blackout in snorkelers who hyperventilate is well-documented)

A surprising number of freediving fatalities occur in shallow water — 2 to 5 metres — where the diver (or observers) assumed depth posed no risk. This assumption is incorrect. Depth is irrelevant. Lack of a competent buddy is the risk factor.

What Is Shallow Water Blackout?

Shallow water blackout (SWB) is loss of consciousness caused by hypoxia (critically low blood oxygen) during the ascent phase of a breath-hold dive. It is one of the leading causes of freediving fatalities worldwide.

The Mechanism

During a freedive, two things happen related to gas pressures:

1. Descent: As the diver goes deeper, water pressure increases. This compression raises the partial pressure of oxygen in the blood — artificially increasing the diver's perceived oxygen level. The diver feels fine and may feel less urgency to ascend than their actual oxygen state warrants.
2. Ascent: As the diver rises and pressure decreases, the oxygen partial pressure drops. In the final metres of ascent — often at 5–10 metres — the partial pressure can fall below the threshold for consciousness. The diver loses consciousness without warning, mid-ascent.

There are typically no clear warning signs. Some divers experience a brief tunnel vision or "greying out" (loss of motor control, or LMC — distinct from full blackout). But many simply lose consciousness with no prior sensation.

Why It's Called "Shallow Water" Blackout

The name is slightly misleading — SWB can happen at any depth, but it most commonly occurs in the shallower portion of the ascent, typically 5–10 metres from the surface, where the pressure change is most rapid. Divers and observers who believe shallow water is inherently safe are exactly the people at risk.

Recovery Without a Buddy

Without a buddy, an unconscious freediver will remain face-down in water. Without immediate intervention, drowning follows within 2–4 minutes. With a trained buddy on the surface watching the dive, rescue is typically straightforward — position the diver face-up, clear the airway, and recovery breathing begins spontaneously in most cases.

Hyperventilation — Why It Kills

Hyperventilation — rapid, deep breathing before a dive — is responsible for a significant proportion of freediving fatalities. The mechanism is specific and important to understand.

The urge to breathe in humans is driven primarily by carbon dioxide accumulation in the blood — not oxygen depletion. When you hyperventilate, you blow off CO2, reducing blood CO2 levels dramatically. This delays the urge to breathe. It does nothing to increase the oxygen in your blood.

The result: a hyperventilating diver can extend their breath-hold significantly past the point where their oxygen is critically low. They feel comfortable — because their CO2 is low — while their oxygen is quietly dropping toward the blackout threshold.

The correct pre-dive breathe-up uses slow, relaxed, natural breathing — not forced or rapid. No more than two or three full, relaxed exhalations followed by a comfortable last breath in. The goal is a relaxed state, not CO2 washout.

If your dive buddy is hyperventilating before dives, correct them. This is not a technique optimisation — it is a safety matter.

The Buddy System in Practice

The buddy system for freediving has specific mechanics. It is not the same as scuba buddy diving, where both divers are in the water simultaneously. Freediving uses a "one up, one down" protocol (see below), but the surface supervision has precise requirements:

Surface Buddy Responsibilities

• Active watching: The surface buddy watches the diver from the moment they begin breathe-up through the entire dive and until the diver gives the OK signal after surfacing. No distractions — no phone, no conversation, no looking elsewhere.
• Positioning: Stay close to where the diver will surface — within 3–5 metres. In ocean conditions with current, adjust for drift.
• Count the time: Know your buddy's expected maximum dive time and begin counting when they submerge. After the expected time plus 30 seconds, begin rescue protocols.
• Readiness to act: Know rescue protocol before every session. Every buddy pair should practice rescue technique before diving.

The OK Signal

After surfacing, every freediver must give an explicit OK signal before the buddy considers the dive complete. Standard signals:

• Hand on top of head (circle with arm)
• Thumbs up
• Verbal "OK"

The buddy confirms with the same signal in return. Until this exchange happens, the surface buddy's attention does not break. The diver removing their mask, spitting out their snorkel, or beginning to talk does not replace the explicit OK signal — a diver experiencing LMC may do these things reflexively while not actually conscious.

Surface Intervals — The 2:1 Rule

Oxygen debt and hypoxia are cumulative over a dive session. Each dive depletes oxygen and creates physiological stress. Adequate rest between dives allows normalisation.

The minimum surface interval rule: rest at least twice the duration of your dive before diving again. A 2-minute dive requires 4 minutes rest minimum. A 3-minute dive requires 6 minutes.

This is a minimum, not a target. Many experienced freedivers use a 3:1 ratio when pushing depth or duration. Factors that increase the required rest include:

• Deep dives (greater physiological stress)
• Long dives (near maximum breath-hold time)
• Cold water (increases metabolic demand)
• Multiple consecutive long dives
• Physical exertion between dives

If you feel breathless, light-headed, or unusually tired at the surface — rest longer. These are your body's signals. Ignore them and the risk of blackout on the next dive increases significantly.

The OK Signal Protocol

The full OK signal protocol is worth knowing in detail:

1. Diver surfaces
2. Diver performs recovery breathing (3 slow, full breaths)
3. Diver signals OK (hand on head, thumbs up, or verbal)
4. Buddy returns OK signal
5. Only now does the buddy relax attention

Recovery breathing must happen before the OK signal — not simultaneously. Three full, slow, controlled breaths to replenish oxygen and normalise CO2, then the signal. Rushing straight to the OK signal (or the buddy accepting an immediate signal before recovery breathing) defeats part of the protocol's purpose.

One Up, One Down

Only one diver should be at depth at any given time in a dive session. When one diver is underwater, their buddy remains at the surface and watches. The dive order alternates: one diver completes their dive, gives the OK, rests the required surface interval, then the second diver goes.

This protocol ensures there is always one person at the surface with full attention on the diver below. If both divers are underwater simultaneously — a practice that does happen informally, particularly in snorkeling — neither can rescue the other in the event of blackout.

Pool Training Safety

Pool freediving carries the same blackout risks as ocean diving. Additional considerations:

• Most public pools do not have lifeguards trained in freediving rescue — your buddy is your sole safeguard. Do not rely on pool staff.
• Hypoxic training in pools (extended static apnea, CO2 tolerance tables) requires a trained, dedicated surface buddy at all times. No exceptions.
• Never practice breath-holds alone in any body of water — bathtub, spa, pool, or ocean. People have died doing exactly this.
• When training CO2 tables, inform your buddy of the training protocol and the expected maximum breath-hold time for each repetition.

See our pool training locations guide for Melbourne venues that support freediving sessions with appropriate space for buddy diving.

Ocean & Open Water Safety

Open water adds hazards beyond hypoxia:

• Boat traffic: Use a dive flag (SMB — Surface Marker Buoy) when freediving in areas with any boat traffic. Victorian law requires this. The flag is only useful if it is visible — use a bright orange or red flag on a float that rides high above the water.
• Currents: Know the tidal state before diving at any site with current. Plan your dive so the return is with or across the current, not against it when tired.
• Surge and swell: At exposed sites, surge can push divers into rocks. Know your exit before entering. Never get between reef and the shore in surge — swim parallel to shore and exit where the surge works with you.
• Conditions assessment: Check BOM marine forecasts before any ocean dive session. If conditions have deteriorated from the forecast on arrival, do not dive. Conditions change faster than forecasts.
• Cold water: Cold shock from sudden immersion in 13°C water can cause involuntary gasping and hyperventilation. Enter the water slowly and allow your body to adjust before beginning breathe-up.

Emergency Response — What to Do If Your Buddy Blacks Out

This is the practical knowledge every freediver must have before diving. Practise this with your buddy before the session — not after something goes wrong.

1. Do not panic. Response time matters. A composed rescue is a fast rescue.
2. Approach from behind or the side. An unconscious diver may inhale water if turned face-up abruptly — keep their face above water throughout.
3. Lift the face clear of the water. The airway must be open. Tilt the head back gently to open the airway.
4. Call for help. If others are present, shout for assistance and ask someone to call emergency services (000 in Australia).
5. Begin rescue breathing if trained. Two rescue breaths while maintaining the diver's face above water. Continue regular rescue breaths until the diver begins breathing independently or emergency services arrive.
6. Recovery position. Once the diver is breathing, place them in the recovery position (on their side) to prevent aspiration if they vomit.
7. Get the diver out of the water. Even a conscious diver who has experienced LMC or blackout should exit the water immediately. Do not allow them to continue diving that session.

Rescue breathing and CPR training are strongly recommended for all freedivers. Many Melbourne freediving schools include basic rescue skills in their courses. If yours did not, First Aid + CPR courses are available through St John Ambulance and the Red Cross throughout Melbourne.

Frequently Asked Questions

For more on the physiological side of freediving safety, see our Is Freediving Dangerous? guide. For breath-hold training that builds your capacity safely, see our breath hold training guide.