No one wants to talk about it

What Causes Freediver Blackout?

by Julie Richardson
Freediving blackout

Simplified, freediver blackout is the result of oxygen starvation at the end of a breath-hold dive. As a diver descends to depth the increasing water pressure causes an increase in overall oxygen pressure, even as oxygen is being consumed. However, during ascent with water pressure and oxygen pressure decreasing, and oxygen supplies running low at the end of the dive, blackout can come on quickly with little or no warning.

The diver will experience the greatest decrease in oxygen pressure at about 30 ft (9.1m) below the surface and shallower. After the diver inhales air at the surface, it takes about 20 heartbeats for the fresh oxygen to make it to the brain. Until this circuit is complete, the diver continues to be in danger of blackout even though he is breathing and may have even signalled to his buddy that he is ‘okay.’

Freediver blackout is a risk every spearfisher accepts, yet too few people engaged in the sport feel comfortable talking about it. Statistics reveal that everyone who freedives is at risk, yet too many spearfishers are unwilling to accept that the risk of blackout applies to them. This fact concerns me.

Because I know that until more divers believe they are at risk and adopt safe diving practices, I will continue to receive freediver fatality reports of brothers, sons, fathers, and husbands – most of them at the top of their game – taken far too soon.

My own sons nearly lost their lives on a 90 ft (27.4 metre) dive as one brother tried to rescue the other, resulting in both blacking out. Friends pulled my boys out of the water blackish blue and unresponsive, their wide-open eyes staring lifelessly at them. The brothers were medivaced under life support to a hospital, where they eventually both fully recovered.

That year there were 35 breath-hold incidents reported in the US. Only three of these 35 divers survived blackout. My sons were two of them. My family has seen the face of blackout and near death. We have suffered through the trauma. And as a result I am passionate about sharing what I have learned so that together we can begin to make this great sport safer for the participants.
Free diving blackout

Dr Neal Pollock from Divers Alert Network (DAN) has maintained a breath-hold incident database since 2005. Not everyone knows about this database, so we are only able to look at reported fatalities, which are estimated to be only a fraction of actual worldwide numbers. But reported fatal and near-fatal events have tripled since the database was started six years ago. Who are the victims? Primarily men age 20-50, and predominantly experienced divers who spearfish.

So what can we do to protect ourselves? I recommend investing in a professional freedive course. Or investing in the Freedivers Recovery Vest (

). Or both. If you lack the resources for these investments, below is a list of safety guidelines, which I compiled after much research into the common triggers of fatal events. This list is not intended to be comprehensive, but if a diver follows these guidelines, the risk of a fatal blackout will be significantly reduced.

Dive With A Buddy

Choose a dive partner with skills and abilities that closely mirror your own, or conform to the level of the least capable diver. Be aware of each other’s limitations and don’t be lured into taking unnecessary risks because your buddy has your back. Never dive alone. In extreme conditions (depth, visibility, current), have additional support on the surface.

Take Turns

Divers should practice diving one up, one down. A diver should receive constant and direct supervision by a partner before, during, and after a dive before the partner begins their dive and the roles are reversed.

Wait 30 Seconds

freediving blackout

After surfacing, a diver should be observed for 30 seconds. This is the time it takes for the heart to pump inhaled oxygen to the brain. Until this circuit is complete, divers remain at risk for blackout even if they signal they are okay. Many blackouts occur at the surface.

Breathe Sensibly

Excessive pre-dive breathing can critically lower carbon dioxide – the trigger that tells the body it’s time to breathe.

Delaying the drive to breathe can cause a diver to stay down too long, leading to blackout.

Weight Properly

Overweighting will cause a diver to sink after blackout. This complicates a successful rescue, often resulting in fatality. Being over-weighted can also cause divers to burn more oxygen, as they work harder to stay off the bottom while hunting, and again on ascent. Because blackout most often occurs on ascent, 30 ft (9.1m) from the surface and shallower, it is best for divers to be neutrally buoyant at 30 ft so that in a blackout they have a good chance of floating up to and on the surface where rescue is possible. To determine if you are properly weighted, adjust your weight at the surface until you are positively buoyant after fully exhaling.

Ditch Your Belt

When a diver feels at risk, or is involved in a rescue, the weightbelt should be immediately released to eliminate all impediments to a good outcome. In a rescue, the victim’s belt should also be released.

Rest Between Dives

The body needs time to recover from oxygen depletion and carbon dioxide buildup. A diver should remain at the surface twice as long as the last dive time to allow for tissue re-oxygenation and to offload carbon dioxide buildup.

Be Prepared

Every member of a dive team should know how to handle a marine based emergency. It is a good idea to review partner rescue and other safety procedures so that these skills become instinctive when you find yourself involved in a rescue.

Every spearfishing fatality is tragic, particularly because following these simple guidelines can prevent most deaths. It is the responsibility of every diver who is exposed to dive safety education to practice dive safety and to share it with fellow divers. And teaching the next generation of divers – our children and grandchildren – how to enjoy this great sport safely can ensure.

Julie Richardson lives in Florida with her husband and three sons. She speaks regularly at conferences and dive shows, and has been published in freedive/spearfishing magazines worldwide. The National Water Safety Congress presented their 2010 National Award to Julie for her outstanding work in water safety through DiveWise, the nonprofit she founded after her boys’ dive accident.

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