Electrical injuries, which may be fatal, can arise from low-voltage currents (i.e., in the home and workplace) or from high-voltage currents carried in power lines or by lightning. Injuries are of two types: (1) burns and (2) ventricular fibrillation or cardiac and respiratory center failure resulting from disruption of normal electrical impulses. The type of injury and the severity and extent of burning depend on the amperage of the electric current and its path within the body.
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Voltage in the household and the workplace (120 or 220 V) is high enough that with low resistance at the site of contact (as when the skin is wet), sufficient current can pass through the body to cause serious injury, including ventricular fibrillation. If current flow continues long enough, it generates enough heat to produce burns at the site of entry and exit as well as in internal organs. An important characteristic of alternating current, the type available in most homes, is that it induces tetanic muscle spasm, so that when a live wire or switch is grasped, irreversible clutching is likely to occur, prolonging the period of current flow. This results in a greater likelihood of extensive electrical burns and, in some cases, spasm of the chest wall muscles, producing death from asphyxia. Currents generated from high-voltage sources cause similar damage; however, because of the large current flows generated, these injuries are more likely to produce paralysis of medullary centers and extensive burns. Lightning is a classic cause of high-voltage electrical injury.
Radiation is energy that travels in the form of waves or high-speed particles. It has a wide range of energies that span the electromagnetic spectrum; it can be divided into nonionizing and ionizing radiation. The energy of nonionizing radiation, such as ultraviolet (UV) and infrared light, microwaves, and sound waves, can move atoms in a molecule or cause them to vibrate but is not sufficient to displace electrons from atoms. By contrast, ionizing radiation has sufficient energy to remove tightly bound electrons. Collision of these free electrons with other atoms releases additional electrons, in a reaction cascade referred to as ionization. The main sources of ionizing radiation are (1) x-rays and gamma rays, which are electromagnetic waves of very high frequencies, and (2) high-energy neutrons, alpha particles (composed of two protons and two neutrons), and beta particles, which are essentially electrons. At equivalent amounts of energy, alpha particles induce heavy damage in a restricted area, whereas x-rays and gamma rays dissipate energy over a longer, deeper course, and produce considerably less damage per unit of tissue. Some of the total dose of ionizing radiation received by the U.S. population is human-made, mostly originating from medical devices and radioisotopes. In fact, the exposure of patients to ionizing radiation during radiologic imaging tests roughly doubled between the early 1980s and 2006, mainly because of much more widespread use of CT scans.
Ionizing radiation is indispensable in medical practice, but this application constitutes a two-edged sword. Radiation in this form is used in the treatment of cancer, in diagnostic imaging, and as therapeutic or diagnostic radioisotopes. However, it also is mutagenic, carcinogenic, and teratogenic.
The following terms are used to express exposure, absorption, and dose of ionizing radiation: • Curie (Ci) represents the disintegrations per second of a spontaneously disintegrating radionuclide (radioisotope). One Ci is equal to 3.7 × 1010 disintegrations per second.
Gray (Gy) is a unit that expresses the energy absorbed by a target tissue. It corresponds to the absorption of 104 ergs per gram of tissue. A centigray (cGy), which is the absorption of 100 ergs per gram of tissue, is equivalent to the exposure of tissue to 100 rads (R) (“radiation absorbed dose”). The cGy nomenclature has now replaced the rad in medical parlance.