Scientists were driven by personal tragedy and near-tragedy to engage a key collective of experts in the field to write a new, definitive report, emphasising that:
Anyone- including young, fit, healthy people, can lose consciousness underwater.
Education and supervision can reduce the risks.
Guidance to the community is essential.
For many, swimming is a source of joy and freedom, but holding your breath in shallow water can be fatal.
In July 2022, Andrew Baker, a professor working on cardiovascular disease, and his daughter had to rescue and resuscitate his son George after he lost consciousness swimming underwater in a pool. "None of us had ever heard of Hypoxic Blackout or knew of the risks George was taking," explained Andrew. "We were so lucky that the situation allowed a complete recovery for George. I can't imagine life without him, but I think about that every single day." He contacted Professor Hugh Montgomery , who lost his son to the water in 2020.
Professor Montgomery, said: "Oscar, my 17-year-old son, was extraordinarily fit - a keen rugby player whose true passion was the sea. He'd been swimming since the age of three, first used a mask and snorkel at four, and was a skilled spear fisher by twelve."
"By sixteen, every spare moment, even over Christmas, was spent in the water - no matter how cold or rough. He died snorkelling in calm, clear waters".
Together, they initiated the creation of a new report - published today in Experimental Physiology - to raise awareness of the risks and how to avoid them. "It aims to present information which can help others enjoy the water just as much as Oscar did, whilst also helping to keep them that bit safer," added Hugh.
Shallow water blackout (SWB) and hypoxic blackout (HB) can be fatal. They usually occur near the surface of the water. Lead author, Professor Mike Tipton from the University of Portsmouth's Extreme Environments Laboratory ( School of Psychology, Sport and Health Sciences ) and chair of the National Water Safety Forum (NWSF) , said: "Everyone is at risk, including the young, fit, and healthy. The key to preventing a problem is understanding how it happens. For both HB and SWB, this means figuring out the physical and biological reasons they occur - in other words - the cause of death."
"HB typically occurs during breath-hold swimming, such as swimming lengths underwater", added Professor Tipton. "When muscles work, they use oxygen and oxygen levels in the blood can drop rapidly especially when working hard and holding your breath underwater. This rapid fall means that the time between the initial drive to breathe and unconsciousness can be very short. If the drive to breath is overridden to achieve a goal (e.g. distance swum underwater) unconsciousness and drowning can occur".
"SWB occurs during breath-hold diving (e.g. free-diving or spear fishing) when returning to the surface. The reduction in pressure near the surface causes oxygen levels to fall and can result in unconsciousness and drowning. Hyperventilating just before a dive increases the risk because it removes carbon dioxide from the body and therefore delays the urge to get back to the surface and breathe".
The report identifies several preventative measures that could reduce the risk of serious incidents.
Recommendations for pool swimming include:
Pool users should be warned about the dangers of extended breath-holding
Lifeguards should discourage distance swimming underwater or remaining underwater for an extended period
Extended breath-holding should only be permitted in a structured, organised session led by a competent instructor or coach
Club "Lung buster" training drills where the swimmer holds their breath for 50 metres at a time and repeat multiple times - should be avoided or very closely supervised.
Recommendations for open water swimming include:
Coaches, lifeguards and competent lifesavers should be prepared to act, and should have ready access to
Rescue equipment
First aid equipment and a defibrillator
They should:
Be competent to complete a full risk assessment of the site and match that with the person(s) undertaking the activity
Agree on the signal for help with the swimmer
Swimmers should fully understand the risks, and should:
Always swim with a "safety buddy"
Wear appropriate personal protective equipment that assists with visibility
Enter the water slowly
Start with a gentle and slow process to assess individual's capability and understanding of the activity
Allow enough time between each activity to fully recover
Never hyperventilate before submerging.
Be aware of the advice provided above and educate yourself about SWB and HB
Know the early signs of SWB and HB and do not attempt to override them
Undertake specialist training before diving, including free diving
Never dive or snorkel alone, although it is recognised that in some cases (e.g. spear fishing) you may end up some distance from others for safety reasons
Recommendations for breath-hold diving and snorkelling include:
Be aware of the advice provided above and educate yourself about SWB and HB
Know the early signs of SWB and HB and do not attempt to override them
Undertake specialist training before diving, including free diving
Never dive or snorkel alone, although it is recognised that in some cases (e.g. spear fishing) you may end up some distance from others for safety reasons
The publication stresses that prevention of SWB and HB requires proper education about these conditions and awareness of their early symptoms such as an urge to breathe and clouding of consciousness, which should never be suppressed or ignored.
