Electric Shock Drowning (ESD) is a form of waterborne fatality that involves paralysis of the body caused by AC current. The ultimate result is that a person in the water becomes unable to swim and often drowns as a result. This current is produced by voltage gradients in the water which are caused by electrical faults in the marine environment. Since saltwater is so conductive, the voltage gradients in salt water are normally low enough so as not to present a danger to people in the water. Our research has revealed that this only occurs in freshwater and includes 45 deaths and more than a hundred casualties (see list at the following link: Electric Shock Drowning Incident List). We know of no other list or data base for this area.
To establish a voltage gradient in the water, 2 things must happen. First there has to be some form of electrical fault which causes the connection of an energized conductor to a metallic object connected to the boat's grounding system. The extent of the fault is such that it is not large enough to cause a circuit breaker to open, therefore the faulted condition continues unchecked indefinitely. This type of fault is known as an undetected ground fault. Second there has to be a failure in the grounding system which is designed to route dangerous fault currents harmlessly back to the source. Routing these fault currents back to their source acts to prevent establishing voltage gradients in the water.
When the two conditions above are established, a boat's or dock's grounded underwater metals become energized relative to the source's grounding system. The difference in voltage between these metals is what sets up the dangerous voltage gradients in the water. If a person in the water finds their way into one of these gradients, an AC current will pass through the body. If this current is high enough, nominally in the range of 12-16 milliamps (that's thousandths of amps), paralysis is likely, resulting in the inability to remain afloat followed by drowning.
Electric shock drowning does not show up in a post mortem since there are no physical effects to the body which can be detected. In all cases, the death is attributed to drowning. It is only in the cases where witnesses are available to identify electric shock as a circumstance that ESD becomes the official cause. Based on this, we estimate that scope of ESDs may be far more widespread than our research data indicates.
We have been selected to participate in a USCG Safety Grant to study ESD and recommend solutions to enhance personal protection in the marine environment. However there are steps that can be taken now to provide better protection for people who find themselves in the water around docks and boats powered with electricity.
First, swimming around docks which supply electrical power to boats and docks must be prohibited.
Second, marinas are required by NFPA 303 (refer to the safety section of this website by following this link: Safety) to conduct annual inspections which examine electrical safety aspects of a marina's electrical system. This includes an annual check of grounding system integrity. Unfortunately most marinas are unaware of this National Electric Code requirement, and of those that are, only a small percentage comply.
Third, today's technology provides for the 24/7 monitoring for electrical ground faults in a marina system. The equipment is known as the Marina Guard. More information on this equipment and further background is available at the following website: http://www.marinaguard.net.
Please contact us for more information in this area including a source of specialized training for marina personnel.