Unlike conventional electric shock, wherein the victim’s heart is stopped or goes into ventricular fibrillation as a result of exposure to a sufficiently high level of electric current, electric shock drowning (ESD) simply paralyzes the voluntary muscle reflexes. It’s important to understand the differences.
In a now well-known case, which occurred in 1999, a 9-year-old boy was electrocuted as he swam adjacent to a marina dock located on fresh water. He was wearing a life jacket and his face never touched the water, making this a straightforward electrocution. His mother jumped in to save him and as she did so, her limbs and extremities went numb. She was exposed to the early stages of ESD, and had she been unable to swim away from the electric current field, she may have drowned. In spite of this, she was able to pull her son to the dock, where others helped pull them from the water.
The ensuing investigation determined that this unfortunate tragedy occurred because of an electrical fault in a nearby unbonded (ungrounded) boat. A DC wire with improper overcurrent protection melted into an AC wire, and in turn allowed AC shore power current to leak into the DC system, and then into the water around the boat and the nearby dock where the boy was tubing (he had fallen off the tube and was swimming to the dock). While in seawater such electric “leaks” fan out, reducing their gradient of intensity, because this was fresh water, the current made its way in a narrowly focused field back to its source, when the boy entered its path.
Thanks to its saline content, the human body is a much better conductor than fresh water, offering the leaking current a lower resistance path, lower than fresh water, which is a comparatively poor conductor.
Had the vessel with the offending electrical fault been properly bonded, it’s likely this tragedy would never have occurred. The fault current would have passed safely ashore over the green safety-grounding wire, where it would likely have tripped the dockside circuit breaker. Similarly, if the vessel had been equipped with a shore power transformer, the leaking current would have returned to it rather than through the water, preventing this tragedy. If no other lesson is learned from this sad tale, let it be this: Never swim in a marina or adjacent to docks where shore power is present.