A lightning bolt is produced when the charged undersurface of a thundercloud sends its electrical charge to the ground. Since the undersurface is usually negatively charged, virtually all discharges are also negative. Approx-
imately 5% of lightning flashes, however, are positive discharges. These are most frequent in mountainous regions.
A lightning bolt may injure or kill an individual by a direct strike, a side flash, or conduction through another object. An example of the last instance would be a lightning bolt's hitting a crane, with the electricity's flowing down the metal structure and striking a grounded worker who is touching the crane. The injuries produced would be the same as if the crane had hit a high-power electrical line, that is, burns at the entrance and exit sites, often multiple and severe.
In a side-flash strike, the bolt of lightning hits an object, such as a tree, and then ricochets, striking the individual. In a direct strike or a side-flash strike where the individual is relatively close to the object from which the bolt jumps, the current can either spread over the surface of the body or enter it, or it can follow both routes. In most cases seen by the forensic pathologist, the current has both flowed over the surface of the body and entered. In such cases, it is quite common to find the clothing torn, shoes burst, hair seared, burns on the skin caused by zippers and other metal objects heated by the lightning, and burns caused by the entrance and exit of current. Cutaneous burns are not severe but always present.11 On histological examination, the epidermis is separated from the papillary dermis. Rupture of the tympanic membrane is present in approximately 81% of cases.11 Objects constructed of ferrous metal on the body may be magnetized. Other metal objects, such as coins, may show burns. The torn clothing and burst shoes sometimes have led to misinterpretation of the nature of the injuries. People struck by lightning and found next to a road have been thought to be hit-and-run victims. If one is inside a metal vehicle, such as a car or train, when it is struck by lightning, the probability of injury is extremely small. On rare occasions, death or injury has been reported when an individual was using a telephone and the line was hit by lightning.12
Deaths from lightning are caused by high-voltage direct current. Death is caused by cardiopulmonary arrest or electrothermal injuries. With a direct hit by lightning, death is probably inevitable, because of burns and injury to the respiratory center of the brain. Amperage in this case would be in the kiloampere range. If the electrocution is secondary to a close point of impac-tion, survival may be possible. In fact, most individuals injured by lightning do survive. One of the lesions considered pathognomonic for lightning injury is the "arborescent" or fern-like injury of the skin called Lichtenberg figures (Figure 16.3). This lesion is a patterned area of transient erythema that appears within 1 h of the accident and then gradually fades within 24 h. The erythematous marks are not burns. Ten Duis et al. believe that this lesion is caused by positive discharges over the skin.13 They hypothesize that the lesion occurs when an individual struck by a negative lightning bolt is then hit by a secondary positive flashover from a nearby grounded object. Another possibility is that it represents an entrance point in an individual struck by a positively charged lightning bolt. Both explanations, neither of which are exclusive of the other, would explain the relative rarity of the arborescent lesion in individuals struck by lightning.
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