MICHELLEHAYWOOD
Divers on the storm
SCUBA ’ s science writer Michelle Haywood looks into the threats faced by divers when electrical storms occur in coastal areas
Lightning is far more likely to hit the land than the sea . Although the sea makes up 70 % of the Earth ’ s surface , NASA has estimated that only 2 % of lightning strikes occur over the water . It is rare for lightning strikes to occur in deep water areas , but near the coast , strikes can be more common . Summer weather conditions with heat and updrafts tend to create more storms with lightning and , of course , that ’ s the time we are most likely to be out on a boat or in the water . So , how scared should we be ?
A typical lightning strike can be around 300 million volts and 30,000 Amps . That ’ s easily enough to kill a human . When lightning strikes the sea , most of the electrical discharge radiates across the surface and this is the area where the greatest risk occurs . It ’ s been estimated that the very high-risk radius is around six metres from the strike , but the radius can extend up to 100 metres .
The electric current has to pass through your body to do you any harm , but the conductive sea water will carry much of the current around you . You are at greater risk if you are above the water in a boat , or on a paddleboard or windsurfer . Being immersed in the water actually lowers your risk , and the deeper you are reduces your exposure to the current .
We also need to consider the sound wave that a lightning strike generates . A strike at the surface creates a sound that is around 260 decibels , which is twice as loud as a gunshot . And we all know that sound travels well through water . There is some research that suggest cod lose their hearing from noises above 180dB ( decibels ), and for other species this may be around 220dB .
Lightning strikes near space shuttle Endeavour at Cape Canaveral
There has been some research to suggest that fish take refuge in deeper water when storms whip up sea conditions , so it ’ s likely that they are further away from the point of the strike . Even being within 100 metres of the strike could still expose them to that dangerous sonic level .
Divers at the surface are at risk of their cylinder being struck by lightning . In 2007 in Florida , a diver died when the lightning struck him as he surfaced . Obviously , the highest point of the diver is at risk , and for many of us hanging vertically in the water that ’ s either our head or cylinder . And given that scuba divers have a finite supply of breathing gas , attempting to stay underwater and wait out the storm isn ’ t practical . Being covered in non-conducting neoprene can help protect the diver to some extent , but it ’ s still not an experience that any of us would seek out . But what about being on a boat in a storm ? Different boats are at different levels of risk from lightning strikes , with trawlers at the highest risk . But in open sea , a boat presents the highest conductive point and may become the target for the lightning discharge . For many dive boats , the VHF antenna is usually the point of contact .
Some boats have lightning conductors installed to move the current away from risk areas such as passenger cabins . The lightning will take the path that allows it to travel through the boat and find its way to the water . Often the exit path is through the prop or rudder , so aside from some damage to the paint , the running gear isn ’ t compromised . Spilt fuel in the bilges can , however , present a risk for causing an explosion . Boats made of steel have an automatic ground in their hull , but wooden or fibreglass vessels are more at risk . The exiting lightning can even punch holes through the hull .
Electrical devices on boats can be affected if the lightning discharge is close . Lightning generates a powerful electromagnetic field and can induce currents in cabling . A boat doesn ’ t even have to suffer a direct hit to experience electrical faults . The random nature of electrical faults caused by lightning strikes is sometimes the first clue for boat owners to indicate their unattended vessel has been struck .
We all know the advice for keeping safe in a storm on land . Don ’ t shelter under trees or tall objects , avoid being near lightning rods , metal fencing etc . On a boat , you ’ re best to get to port and get off . But if the shore is out of reach , drop anchor , remove any jewellery , put on life jackets and get low in the centre of the boat . If the boat has a cabin , stay inside . �
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