Before you spearfish — this comes first
- Get proper instruction before you spearfish. A recognised freediving or spearfishing course teaches the things that actually kill people in this sport, and reading about them is not the same as being taught them.
- Dive with a buddy, and dive one up, one down — one diver in the water, one on the surface watching them, every dive. A breath-hold blackout is silent and gives no warning; a watching buddy is the difference between an incident and a fatality.
- Stay inside your own training and experience. Depth and breath-hold times are personal, they change day to day, and nobody else's numbers apply to you.
- Understand the conditions before you enter the water: visibility, current, swell, tide, boat traffic and your exit. Conditions decide whether a dive is reasonable far more often than skill does.
- Use equipment you have been shown how to use, check it before every session, and be visible — a marked float and line are how boat traffic knows you are there.
- Never extend a dive for a fish. No catch is worth pushing a breath-hold, and the urge to take one more second is exactly what a blackout feels like from the inside — which is to say, like nothing at all.
Equalisation, and the injuries that follow forcing it
Explainer · Last reviewed 2026-08-17
Pressure rises fastest in the first few metres, and the injuries come almost entirely from continuing to descend when equalisation has failed — which makes stopping the whole of the technique that matters.
Safety
Barotrauma and pressure injury — Can cause injury needing treatment
Failing to equalise while descending pulls the eardrum inward and can perforate it, and produces sinus and mask barotrauma. A perforated eardrum in cold water can cause disorienting vertigo.
What reduces it: Equalising early and often from the surface, stopping the descent the moment equalisation fails, ending the dive rather than forcing it, and not diving while congested.
Descending compresses the air in the middle ear, the sinuses and the mask. Unless that air is replaced, the pressure difference pulls the eardrum inward and the tissue lining the sinuses towards the space, which is what the pain is.
The rate of change is greatest near the surface. Going from the surface to ten metres doubles the ambient pressure; going from thirty to forty metres changes it by a third. That is why most equalisation problems occur in the first few metres and why descending head-first requires equalising early and often rather than waiting for discomfort.
THE INJURIES. A middle-ear barotrauma ranges from discomfort to a perforated eardrum. Sinus barotrauma produces pain and bleeding. Mask squeeze — failing to exhale into the mask — produces bruising around the eyes and burst surface vessels. All are avoidable and all are common in self-taught divers.
THE RULE THAT PREVENTS ALL OF THEM: if equalisation fails, stop descending. Ascend slightly, try again, and if it still fails, end the dive. Forcing it is how eardrums perforate, and a perforated eardrum in cold water can cause disorientation severe enough to be an emergency in its own right.
AND DO NOT DIVE CONGESTED. A cold, allergy or infection makes equalisation unreliable and can produce a reverse block on ascent, where air trapped in the middle ear expands and cannot escape. That is a worse problem than not being able to descend.
What this page will not do
It will not teach an equalisation technique.
Frenzel, Valsalva and the rest are physical skills involving control of the soft palate, glottis and tongue, and they are taught by instructors who can watch, correct and stop a student. Learning them from text is unreliable, and unreliable equalisation practised at depth is precisely how the injuries above occur.
It also does not diagnose. Persistent inability to equalise, pain that continues after a dive, hearing changes, discharge or vertigo are matters for a doctor — ideally one with diving medicine experience — rather than for a fishing platform.
What this page does is state the mechanism, name the injuries, and be unambiguous about the only decision that reliably prevents them: when equalisation fails, the descent stops.
Authoritative guidance
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Guidance on barotrauma of the ears and sinuses in breath-hold diving, and on ceasing descent when equalisation fails.States this directlyPassage read and verified
- BSAC diving safety guidance and annual incident report — British Sub-Aqua Club (Water-safety or diver-training authority)Relied on for: Diving safety guidance including pressure-related injuries and the risks of diving while congested.States this directlyCitation checked — the work exists and is described correctly
Where to go next
Where it matters
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Freediving for spearfishing
A membership assertion rather than a topical one: this record teaches the discipline or its equipment, so the discipline's mandatory safety posture applies to it.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Freediving and breath-hold spearfishing safety practice, including the supervision requirement that applies across the discipline rather than to particular equipment.States this directlyPassage read and verified
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Breath-hold diving safety practice and discipline definition set out by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
Related reading
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Wetsuits, fins and masks for spearfishing
Equipment participates in the pressure system.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diving medicine guidance on ear and sinus barotrauma and on ceasing descent when equalisation fails.States this directlyPassage read and verified
How this compares
- Depth as an environmental variablePressure changes fastest in the first few metres, which is why most equalisation problems happen near the surface.
- Equalisation and pressureOne record covers the mechanism; this one covers what happens when it fails and the descent continues.
What these connections rest on (2)
Authoritative guidance — 2 connections
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Depth as an environmental variable
The rate of pressure change explains where the injuries occur.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diving medicine guidance on ear and sinus barotrauma and on ceasing descent when equalisation fails.States this directlyPassage read and verified
Equalisation and pressure
The technique page and the injury page answer different halves of one question.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diving medicine guidance on ear and sinus barotrauma and on ceasing descent when equalisation fails.States this directlyPassage read and verified
Sources for this page
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diving medicine guidance on equalisation, barotrauma and pressure injuries.States this directlyPassage read and verified
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