|Fig. 1: This is an example of a Lichtenberg figure etched into plexigas. The branching discharges ultimately become hairlike, but are thought to extend down to the molecular level. (Source: Wikimedia Commons)|
When conditions within a thunder head strip electrons from rising water vapor they create an electric field. This field is the origin of lightning. The field is so intense that the negative electrons within the cloud repel the other electrons found on the ground. These electrons found on the ground are pushed so far into the strata that the surface of the Earth becomes positively charged. Once this is the case, molecules of air around the clouds ionize. They discharge the electrical field through a short circuit back to the ground, thus neutralizing the charge difference. This occurrence is what is commonly known as lightning. 
Because humans are good conductors, they are vulnerable to being electrocuted in all sorts of ways ranging from bathtub hairdryer incidents to being struck by lightning itself. While all of these electrocutions are damaging to the human body, lightning strikes differ from most industrial shocks. They differ in several key ways: the level of voltage is much greater in a lightning strike, the duration of the lightning strike is greater, and the location of the injuries sustained are different.  A bolt of lightning generates 300kV, which is much greater than most industrial shocks which generate 20-60kV.  The duration of the shocks also differ. Man made, or industrial shocks usually last about half a second. These shocks last until the human is either blown clear or the circuit breaker trips, ending the shock. In comparison, a lightning strike course through a human at a much faster rate of a mere 3 milliseconds.  The last difference is that most man made shock injuries occur on a person’s hands and arms. Whereas a lightning strike injury will usually occur in a person’s head, shoulder, or upper torso area. 
In addition to the 300kV of energy that course through a person’s body upon being struck by lightning, the power of the strike heats the surrounding air to 50,000°F. This can cause massive burns at the sight of the bolt’s entry, and exit, into, and out of, the human body.  Other injuries suffered as a result of a lightning strike include Lichtenberg figures, shown in Fig. 1, cardiovascular damage, and neurological damage. Lichtenberg figures are lightning bolt-shaped burn marks cause by bursting blood vessels throughout the damaged area of the body. 
Direct lightning strikes cause considerably more damage than other types of shocks. The voltage of the shock is much greater, the duration of the shock is much smaller, and the location of the shock is a more vital body part. This results in more serious burn, cardiovascular, and neurological injuries.
© Nico Corti. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 W. Beasley, M. A. Uman, P. L. Rustan, "Electric Fields Preceding Cloud-to-Ground Lightning Flashes," J. Geophys. Res. 82, 4883 (1982).
 R. D. Hill, "A Survey of Lightning Energy Estimates," Rev. Geophys. 17, 155 (1979).
 R. Lichtenberg et al. "Cardiovascular Effects of Lightning Strikes," J. Am. Coll. Cardiol. 21, 531 (1993).
 P. F. Mellen, V. W. Weedn, and G. Kao, "Electrocution: A Review of 155 Cases with Emphasis on Human Factors," J. Forensic Sci. 37, 1016 (1992).
 B. I. Resnik and C. V. Wetli, "Lichtenberg Figures," Am. J. Forensic Med. Pathol. 17, 99 (1996).