The human body simply isn't built to conduct 300kV of electricity. So when things backfire while you're fishing in a thunderstorm, and you find yourself doing an impromptu rendition of Powder, here's what you can expect.
While there is still debate within the scientific community as to the exact nature of the process, most believe that cloud-to-ground lightning originates when conditions within a thunder head strip electrons from rising water vapour to create an electrical field. Free electrons gather at the bottom of the cloud while positive ions move to the top.
This electrical field is so intense that the negative electrons in the cloud repel electrons on the ground. These ground-level other electrons get pushed far enough into the strata that the surface of the planet becomes positively charged. Once that occurs, air molecules around the cloud ionise, discharging the electrical field via a short-circuit back to Earth, neutralising the charge difference. That's lightning—and you don't want to be anywhere near it when it strikes.
Humans are good conductors. Being comprised of atoms that can transmit electrons is great for our neural network's basic functionality. But it's very bad when we drop a hairdryer in the tub, crack open an industrial capacitor, or become a human lightning rod on the links.
Lightning strikes do, however, differ from the industrial shocks you'd receive from high-voltage equipment. First, the level of voltage is greater in lightning—most industrial shocks generate 20-60kV, but a bolt of lightning generates 300kV. Second, the duration of a lightning strike is much shorter. Man-made shocks last about a half second (500 miliseconds), on average, until the worker is either blown clear or the circuit breaker trips. A lightning strike courses through you in in just 3 milliseconds. Finally, most industrial electrical injuries hit the worker's hands, arms, and shoulders while natural lightning most often strikes the head, shoulders, and upper torso.
When a bolt of lightning does strike a human frame, very bad things happen. In addition to the 300kV of energy coursing through you, the power of the strike heats the surrounding air to 50,000 degrees F, causing third degree burns at the bolt's entry and exit points. It can also create lightning bolt-shaped burn marks, called Lichtenberg figures, which are caused by bursting blood vessels. The heat and force can singe and shred clothing. Lightning strikes have blown people clear out of their shoes.
The damage can be even worse if you are holding a metal object. For one thing, doing so increases the likelihood of being struck in the first place. A big reason Florida leads the nation in annual lightning-related deaths and injuries (126 deaths in the last decade alone) isn't from regional topography but due to the state's vibrant golf industry. Legions of players frantically break out the nine irons to finish the round ahead of an oncoming storm. Second, wearing metal objects while—chains, necklaces, braces...piercings—can cause electrical arcing and rapidly heat, causing serious burns of their own.
Burns aren't the only way lightning will hurt you. A lightning strike can act as a massive fibrillator, upsetting the heart's electrical rhythm and causing cardiac arrest. That's in addition to bursting blood vessels and damaging the cardiac muscles. Fortunately, only one in ten Americans have died from being struck by lightning in the three decades between 1981 and 2010. That period saw 54 fatalities a year on average, though between 2001 and 2010, that number dropped to 39 annually. Ninety percent of lightning strike victims do survive, but at a significant cost.
"Lightning injuries are varied and take many different forms," wrote Dr. Elisabeth Gourbière of the Electricité de France, Service des Etudes Médicales in Lightning Injuries to Humans in France. "The most dangerous (and possibly fatal) immediate complications are cardiovascular and neurologic. It must be kept in mind that only immediate and effective cardiorespiratory resuscitation (started by rescuers), followed as soon as possible by emergency medical treatment, can save victims who are in cardiopulmonary arrest, or avert the serious consequences of cerebral hypoxia. Some victims remain in a coma despite intensive resuscitation and die of secondary causes including hemorrhages and multiple lesions (encephalic, cardiac, pulmonary, intra-abdominal)."
Immediate post-strike symptoms can include caridac arrhythmia, myocardial damage, and pulmonary edema in the circulatory system. Neurologically, you will likely lose consciousness for anywhere from a few minutes to a few years. You could suffer brain damage (because in the cellular structure of your brain literally cooks from the current) resulting in short-term memory loss or amnesia. Longer term neurological maladies include personality changes, learning disabilities, sleep disorders, seizures, Parkansonism (not actual Parkinson's Disease but a similar constant twitch). Last, victims commonly report numbness and weakness in the limbs, temporary or permanent paralysis, concussions, blown ear drums, cataracts, and a whole lot of pain.