34

Injuries from Electromagnetic Energy

STEPHEN A. MCCURDY

Key words: electrocution, electromagnatic energy, non-ionizing radiation, ionizing radiation

Injury occurs when body tissues are subjected to levels of energy outside the normal tolerance bands. Excessive energy damages tissues, potentially beyond repair, and disrupts normal physiologic functioning. Injury may also occur when inadequate energy is available, such as extreme cold leading to frostbite injury, or disruption of normal cellular energy systems such as asphyxiation. Energy may be in the form of mechanical energy (e.g., moving parts of machinery), chemical energy (e.g., caustic substances), heat, poten- tial energy (e.g., working at heights; with a fall, the potential energy is con- verted into mechanical energy as the subject strikes the ground), and electromagnetic energy (e.g., electricity, radiation). The agricultural work environment contains many sources of energy, and agriculture is widely rec- ognized as one of the most hazardous industries in the United States (1–4).

Electromagnetic Energy

Electromagnetic energy is carried at low frequencies in electrons. The energy supplied by electrons is determined by the voltage (the force acting to push electrons through a conductor) and the flow of electrons, known as current. Current flow is measured in amperes or milliamperes (mA). Common resi- dential and industrial machinery uses alternating current, indicating that the flow of electrons alternates in direction, typically at a frequency of 60 cycles per second, or 60 hertz (Hz). A battery, in contrast, supplies direct current, indicating that the flow of electrons proceeds in only one direction. When the frequency of alternation of current flow is high, the electromag- netic energy can escape its conductor and radiate into space, traveling at the speed of light. Here the energy is carried by photons rather than electrons. The behavior and properties of this electromagnetic energy are determined largely by its frequency. The electromagnetic spectrum includes, in order of

477 478 S.A. McCurdy increasing frequency, radio waves, microwaves, infrared (heat) radiation, vis- ible light, ultraviolet radiation, X-rays, and gamma rays. X-rays and gamma rays have extremely high frequency and energy content. As a result, this radiation can strike molecules in the body, knocking away electrons and leaving a damaged, electrically charged (i.e., ionized) remnant. Ionized molecules raise the risk of subsequent mutations and cancer. Accord- ingly, such high-frequency radiation is termed ionizing radiation and has been associated with increased cancer risk. Lower frequency radiation, such as radio waves, visible light, and microwaves, does not cause ionization, and is termed nonionizing radiation. Damage from nonionizing radiation is usually due to simple heating of tissues.

Nonionizing Electromagnetic Energy Sunlight

The most abundant form of environmental electromagnetic radiation is sun- light. The sun emits a broad spectrum of radiant electromagnetic energy. Fre- quencies in the visible light range penetrate the atmosphere and allow us to see. Radiation at frequencies just above the violet, or high-frequency, end of the visible light spectrum can have important health effects. Such ultraviolet radiation can cause acute sunburn. Chronic exposure to ultraviolet radiation prematurely ages the skin and increases the risk for skin cancers. Sunlight- related injuries are an important problem for agricultural workers because of the need to work outdoors.

Prevention of Sunlight Injuries Reduction of exposure to direct sunlight is the simplest and most effective protection against sunlight-related injury. When work must be done in direct sunlight, workers should wear protective clothing, including long pants, long- sleeved shirts, gloves, and broad-brimmed hats to shade the face and neck. This may be uncomfortable on hot days, and workers should be careful to drink plenty of fluids and rest as needed so as to avoid heat exhaustion and sunstroke. Sunscreen should also be used.

Welding Flash Burns

Welding is a common activity in the agricultural work environment; its health effects have recently been thoroughly reviewed. Welding involves heating pieces of metal such that they liquefy and join together. Energy to raise the temperature of the metals may come from electricity (electric arc welding) or from the burning of gases such as acetylene. Temperatures reach several thousand degrees Celsius, and the process generates electromagnetic radia- tion across a wide frequency spectrum. Electric arc welding generates large 34. Injuries from Electromagnetic Energy 479 amounts of ultraviolet radiation. This can lead to an acute keratoconjunc- tivitis (“arc eye”), acute skin burns (“flash burns”) similar to sunburn, and chronic skin damage. The most commonly affected body parts are the face, neck, hands, and forearms. Radiant heat carried by infrared electromagnetic energy may also cause burns and skin damage (5).

Prevention of Welding Flash Burns Welders should wear protective equipment to shield from ultraviolet radia- tion. Long-sleeve upper-body clothing, gloves, and a welding helmet with ultraviolet filter plates for arc welding will minimize exposure and injury. Welding equipment should be well maintained and properly grounded to pre- vent electrocution injury.

Electrocution Injury

The most common source of severe electromagnetic injury on the farm is electricity carried in conducting wiring and used for machinery, light, and heating. Electricity causes injury through several mechanisms. Voltage and current flow disrupt nerve and muscle function. Electrical current stimulates contractions in both flexor and extensor muscles. At currents above 16 mA, the stronger flexor muscles predominate, rendering the victim unable to let go of an energized object they have grasped. Currents of 20 mA may lead to paralysis of respiratory muscles and death. Current at 100 mA leads to ven- tricular fibrillation, lower currents may also lead to fatal cardiac arrhythmias. Current at 2 Amperes and above leads to cardiac standstill and internal organ damage (6). Conduction through the body is facilitated by moist conditions, such as contact with standing water and wet skin or clothing. Under dry condi- tions, the resistance of the body may be sufficient to limit current flow from a 120-volt source to 1 mA, a barely perceptible amount. Under wet conditions, resistance may be lowered to allow over 100 mA of current flow, sufficient to cause cardiac fibrillation. Skin damaged by electrical burns suffers further reduction in resistance, leading to increased current flow and injury (6).

Epidemiology of Electrocution in Agricultural Workers Data from the United States Bureau of Labor Statistics Census of Fatal Occupational Injuries (CFOI) for 1992 to 1999 show a total of 2,525 occu- pational electrocution deaths among all occupations, yielding a mortality rate of 0.23 deaths/ deaths/105 worker-years. With respect to ethnicity, the highest rate was seen among Hispanics (0.30 deaths/105 worker-years), an important observation because a majority of hired workers in agriculture are Hispanic. Of all occupational electrocution deaths, 320 (12.7%) occurred in agricul- 480 S.A. McCurdy tural, forestry, and fishing occupations. The number of such deaths in agri- cultural, forestry, and fishing occupations was exceeded only by those in the construction trades (988 deaths) and transportation and material moving occupations (517 deaths). When these deaths are expressed as mortality rates, the rate for agriculture, forestry, and fishing occupations (1.16 deaths/105 worker-years) is exceeded only by extractive (mining) occupations (2.38 deaths/105 worker-years) and construction trades (2.10 deaths/105 worker- years) (7,8). Within agriculture, the majority of deaths occurred among farm workers (92 deaths, 1.24 deaths/105 worker-years) and groundskeepers and gardeners (91 deaths, 1.50 deaths/105 worker-years). While only 11 deaths occurred among supervisors of farm workers, this group demonstrated the highest mortality rate within agriculture (3.41 deaths/105 worker-years) (7,8).

Common Electrocution Injury Scenarios in Agriculture Electrocution injury occurs when a worker comes into contact with an electri- cally energized source. Risk for electrocution rises when electrical networks and equipment are improperly designed, built, or maintained. Poorly grounded machinery and tools are a common source of electrocution. Workers come into physical contact with the faulty machinery, which carries an electric charge that flows to the ground through the worker’s body. Risk is heightened for work in standing water, such as around pumps or on damp ground. A second common scenario involves accidental contact with power lines. Overhead power lines typically carry between several hundred to several thousand volts, which is stepped down through transformers at various stages to bring either 220 or 110 volts to the point of use. Accidental contact can occur when lines are insufficiently elevated above ground or drop due to wind, storms, or inadequate maintenance. Electrocution injuries also have occurred when workers accidentally brush against the lines with metal lad- ders, pipes, or other tools. Damaged or weathered line insulation may prove inadequate to prevent current flow through the metal tool and ultimately to the ground through the worker’s body. Metal booms and cranes may also contact lines and electrocute workers who come in to contact with them. Grain augers, when moved in an elevated position, may be able to contact high-voltage lines (6,9).

Prevention of Electrocution Injury NIOSH described a series of 224 fatal electrocution incidents from 1982 to 1994 and noted that at least one of five factors was present for all cases. These included:

1. Failure to follow safe work procedures 2. Failure to use required personal protective equipment 34. Injuries from Electromagnetic Energy 481

3. Failure to follow lock-out/tag-out procedures 4. Failure to comply with existing OSHA, or recognized electrical safety code regulations 5. Inadequate safety training (10).

Prevention of electrical injury requires involvement by employers and employees. Electrical equipment should be inspected for safety and proper grounding on a periodic basis. This is especially important for equipment used for water or wet circumstances, such as pumps. Failsafe mechanisms that automatically shut off power to machinery when casings are opened should be incorporated in the design and not defeated by the operator. Work- ers should be certain that power is shut off before beginning maintenance work on electrical equipment. Electrical hand tools should be in good repair and properly grounded with a three-wire electrical system or have doubly insulated casings. Ground-fault circuit interrupters, which halt current flow when current to ground is detected (e.g., through the body of the tool opera- tor), add further protection. Workers should wear dry gloves when operating electrical machinery, especially hand tools such as drills and sanders. In some settings, rubber insulated gloves are appropriate. Grain augers should be in the lowered position when moving to prevent contact with overhead high- voltage wires. Metal ladders should not be used in areas where there is a risk of contact with power lines. Request that the power company de-energize lines, if feasible, where there is risk of contact (6). A comprehensive description of electrical safety regulations and recom- mendations is available in Subpart S 29 CFR 1910.302 through 1910.399 of the General Industry Safety and Health Standards. Subpart K of 29 CFR 1926.402 through 1926.408 of the OSHA construction safety and health standards address electrical equipment and installations used to provide elec- tric power and light at the jobsite. The United States National Electric Code and National Electrical Safety Code comprehensively address electrical safety regulations. Most other countries have similar codes (11,12).

Lightning Injury

Lightning injury is an extreme form of electrocution injury. Tremendous volt- ages build up between the atmosphere and the earth, typically discharging in a spark striking high points, such as buildings or trees. The arcing electricity causes instantaneous superheating of the air, resulting in an explosive flash of visible lightning and thunder. Agricultural workers are at risk for lightning strikes because of their out- door work. Lightning may cause injury through a direct strike, which is usu- ally fatal, or indirectly through current flows that occur in the vicinity of a strike. Indirect electrocution from lightning often causes burns but is not nec- essarily fatal. 482 S.A. McCurdy

Outdoor work should be halted during lightning storms. Workers caught outdoors in a lightning storm should take shelter in a building or car. If shel- ter is unavailable, they should seek low ground, such as gullies, and keep low. Workers should not remain on farm machinery such as tractors and should get out of the water if swimming or boating. It is unwise to seek shelter under lone or prominent trees or other objects. Tools, especially long tools like hoes or metal ladders, should not be carried. Lightning may also cause injury indirectly by downing trees, power lines, or starting fires. Downed power lines should not be handled. If a downed power line strikes a car, the occupant should avoid contact with metal in the car and drive away if possible. If this is not possible, it is safest to remain in the car, avoiding contact with metal, until the line is deenergized.

Ionizing Radiation

Ionizing radiation is uncommon in agricultural settings. Ionizing radiation may be used in food sterilization and decontamination procedures. Excessive exposure to ionizing radiation may lead to acute or chronic radiation sick- ness. Rapidly dividing cells, such as the lining of the gastrointestinal tract and blood-generating cells in the bone marrow, are particularly sensitive to radi- ation exposure. Hence, acute radiation sickness is characterized by gastroin- testinal disturbances, bleeding due to platelet loss, infections due to immune-system damage, and anemia. Exposed skin may suffer acute burns and subsequent scarification. Chronic radiation exposure may be associated with cancer and reproductive abnormalities. Prevention of illnesses and injuries from ionizing radiation involves eliminating or minimizing exposure. Radiation sources should be properly shielded and radiation exposures mon- itored. Persons not educated in working around such sources should not have access.

References 1. Robertson LS. Injury Epidemiology. New York, NY: Oxford University Press, 1992. 2. Hard DL, Myers JR, Gerberich SG. Traumatic injuries in agriculture. J Agric Saf Health 2002;8:51–65. 3. McCurdy SA, Carroll DJ. Agricultural injury. Am J Ind Med 2000;38:463–80. 4. Rautiainen RH, Reynolds SJ. Mortality and morbidity in agriculture in the United States. J Agric Saf Health 2002;8:259–76. 5. Antonini JM. Health effects of welding. Crit Rev Toxicol 2003;33:61–103. 6. National Institute for Occupational Safety and Health. Preventing Electrocution of Workers Using Portable Metal Ladders Near Overhead Power Lines. DHHS (NIOSH) Publication No. 89–110. Morgantown, WV: NIOSH, 1989. 7. Taylor AJ, McGwin G Jr., Valent F, Rue LW 3rd. Fatal occupational electrocu- tions in the United States. Inj Prev 2002;8:306–12. 34. Injuries from Electromagnetic Energy 483

8. Meister JS. The health of migrant farm workers. In: Cordes DH, Rea DF, eds. Occupational Medicine State of the Art Reviews: Health Hazards of Farming. Philadelphia, PA: Hanley and Belfus, Inc., 1991;6:503–18. 9. National Institute for Occupational Safety and Health. Preventing Grain Auger Electrocutions. DHHS (NIOSH) Publication No. 86–119. Morgantown, WV: NIOSH, 1986. 10. National Institute for Occupational Safety and Health. Worker Deaths by Elec- trocution: A Summary of NIOSH Surveillance and Investigative Findings. DHHS (NIOSH) Publication No. 98–131. Morgantown, WV: NIOSH, 1998. 11. National Fire Protection Association. National Electric Code. Quincy, MA: National Fire Protection Association, 2005. 12. American National Standards Institute. National Electrical Safety Code. New York, NY: American National Standards Institute, 2002.