What happens to a body on one breath.

At the surface the air in your lungs is at one atmosphere of pressure. Ten metres down the water adds another; the gas in your chest is now at two atmospheres and occupies half its volume. This is Boyle's law and it is the whole reason freediving feels the way it does: the first ten metres are the most violent change you will ever make, and they happen in the first few seconds.

Because the change is steepest near the surface, the pool is the ideal classroom: sixty metres of depth with none of the sea's variables, and most of the learning in the first fifteen.

Cold water on the face and breath-hold together trigger a set of reflexes shared with seals and dolphins: the mammalian dive reflex. It is not learned. It is uncovered.

• Bradycardia. Heart rate falls, often by a third within the first thirty seconds, in trained divers much further. Less work, less oxygen spent.
• Peripheral vasoconstriction. Blood vessels in the limbs narrow. Oxygen is kept for the heart and the brain, which are the two organs that matter in the next two minutes.
• Blood shift. Under pressure, blood plasma moves into the vessels of the chest and fills the space the collapsing lungs leave behind. This is what lets a human chest survive depths that would otherwise crush it.
• Spleen contraction. The spleen releases its reserve of red cells into circulation. More carriers for the oxygen you have.

The reflex strengthens with use. After a few weeks of regular, relaxed breath-hold it engages faster and deeper, which is one of the two reasons the first line of the practice is slow on purpose.

The thing that makes you want to breathe is rising carbon dioxide, not falling oxygen. The body measures CO₂ well and O₂ poorly. This has two consequences, one useful and one lethal.

The useful one: the urge arrives long before you are in danger. The first contraction of the diaphragm, an involuntary twitch that feels like a hiccup in slow motion, usually comes with more than half your usable oxygen still in the blood. Learning to sit with contractions, calmly, is the core skill of static breath-hold, and it is where the stillness is.

Tolerance to CO₂ trains quickly. Tolerance to low O₂ trains slowly and is never something to test alone. Tables exist for both and are described under training.

The air spaces in the middle ear and the sinuses do not shrink with the lungs. Unless you push air into them to match the water pressure, the eardrum is forced inward and, past a point, torn. Equalising early, often and gently is the first technique anyone learns, and the most common reason a dive turns short.

• Valsalva. Pinch the nose and push with the chest. It works in a swimming pool and fails below about fifteen metres, because the chest has no spare air to push. We teach it only to leave it behind.
• Frenzel. Pinch the nose, close the throat, and use the tongue as a piston to drive the air already in the mouth into the ears. Independent of the lungs, works head-down, works deep. The standard.
• Mouthfill. At twenty to thirty metres, before the lungs reach residual volume, take a last charge of air into the mouth and ration it on the way down with Frenzel. The technique that opens the thirties and forties.

With a thin suit and a little weight you are buoyant at the surface, neutral at around ten to fifteen metres, and negative below. Beyond that point every kick is wasted oxygen. The diver stops, straightens, relaxes every muscle that can be relaxed, and lets the sea take the body down the line.

Freefall is the part people cannot describe afterwards and the reason they come back. There is no sound. The chest is compressed and quiet. Heart rate is low. Nothing is required of you except not to interfere. Members tend to reach it in the second or third month and tend not to talk about it in the car on the way home.

The point where you stop trying is the point where it starts working.Freefall, in one sentence

On the way down pressure concentrates the oxygen in your lungs and the brain is well supplied. On the way up the process reverses: as pressure falls, the partial pressure of oxygen in the lungs falls with it, and the brain can be starved in the final metres even when the dive felt fine. This is hypoxic blackout, formerly called shallow-water blackout. It is silent, it gives little warning, and it happens to strong, fit, experienced people who were diving alone or whose buddy was not watching.

Its milder cousin is loss of motor control: a few seconds of shaking, blue lips, a blank look at the surface. Both are managed the same way, and both are, in this practice, a failure of safety rather than an achievement of depth.

• One up, one down. Your seeb meets you on the ascent at a third of your depth and swims beside you to the surface, watching your face.
• Surface protocol. Grab the line or the buoy, three recovery breaths (short exhale, full inhale, hold a beat), remove the mask or clip, and signal. Thirty seconds of this before anyone speaks.
• Rescue. A blacked-out diver brought to the surface, airway open, face dry, with breath blown across the eyes and a spoken name, nearly always resumes breathing within seconds. Nearly always is the reason the seeb is always there.

Not by holding your breath as long as possible as often as possible. That teaches the body to panic. The method is a slow accumulation of comfort in three places.

Dry, at home

CO₂ tables: a fixed hold, say two minutes, repeated eight times with a shrinking rest between them. The body learns that contractions are survivable. O₂ tables: a fixed rest and a lengthening hold, used sparingly. Both done sitting or lying down, never in water, never in a bath. Ten to twenty minutes, three times a week, is more than enough.

In the pool

Static breath-hold, face down at the surface with your seeb's hand on your shoulder, is where the stillness is learned. Dynamic, swimming horizontally on one breath, teaches economy of movement. Depth in the pool, to fifteen and then twenty metres, teaches equalisation without current, swell or cold.

In the sea

A weighted line, a buoy, a boat, and a seeb. Every session begins at a depth you already own and ends before you are tired. Depth increases by a metre or two when the previous depth has become boring. Boring is the signal; not excitement, not pride, not the calendar.

The pearl diver and the spearfisher do the same thing: descend, settle, wait, decide once, return. Spearfishing on breath-hold is not the drifting of a scuba diver with a gun; it is a few minutes of absolute attention at a time, repeated through a morning, in which the fish you want arrives or does not.

• Agguato. Lie still on the bottom, behind a rock, breath held, and let curiosity bring the fish to you. The purest form, and the one closest to meditation, because nothing you do makes it happen faster.
• Aspetto. Hang in mid-water near a drop-off, motionless, waiting for pelagic fish to pass. Longer holds, deeper water, more patience.
• One shot. You take a fish you will eat, of a size and species you are allowed, with a shot you are sure of. There is no second attempt and no trophy. The fish is cleaned on the boat and eaten the same day.

Every contemplative tradition arrives at the same instruction: attend to the breath, notice the mind wander, return. The difficulty is that nothing enforces it. The mind wanders, and the only cost is that you noticed.

On one breath at depth the instruction enforces itself. There is a single object of attention, the breath you are not taking, and the body makes every other thought expensive. The dive reflex slows the heart in the way an hour of sitting is supposed to. The contractions are the wandering mind, made physical, and the skill of sitting calmly through them is exactly the skill the cushion is trying to teach.

Most members did not come for this. Most members, by the third month, say it is what they stay for.

الغوصGHAUS

The dive; the pearling season of the Gulf, four months each summer. Our name.

النهامNAHHAM

The singer on a pearling boat, who set the rhythm of the crew. Line I: breath.

الحجرHAJAR

The stone a diver rode to the bottom; also the mountains above our sea sites. Line II: depth.

الغواصGHAWAS

The diver. Line III: the hunt.

السيبSEEB

The rope-puller who brought the diver up. Your safety diver, one per member, all season.

الفطامFITAM

The turtle-shell nose clip of the pearl divers. Worn today in plastic.

STA · DYN · CWT · FIM · CNF

The competitive disciplines: static breath-hold; dynamic (horizontal) with fins; constant weight with fins; free immersion, pulling down the rope; constant weight with no fins. See records.

Residual volume

The air left in the lungs after a full exhale. Reached by compression at roughly thirty to forty metres; below it, equalisation needs air stored in the mouth.

Breathe-up

The two to three minutes of slow, relaxed breathing before a dive. Not hyperventilation. Ends with one full breath and a stillness.

LMC · BO

Loss of motor control and blackout: hypoxia at the surface or in the final metres of ascent. Both prevented by a watching partner and an early turn.