*Contact with 20 milliamps of current can be fatal. As a frame of reference, a common household circuit breaker may be rated at 15, 20, or 30 amps.

When current greater than the 16 mA "let go current" passes through the forearm, it stimulates involuntary contraction of both flexor and extensor muscles. When the stronger flexors dominate, victims may be unable to release the energized object they have grasped as long as the current flows. If current exceeding 20 mA continues to pass through the chest for an extended time, death could occur from respiratory paralysis. Currents of 100 mA or more, up to 2 Amps, may cause ventricular fibrillation, probably the most common cause of death from electric shock.¹¹ Ventricular fibrillation is the uneven pumping of the heart due to the uncoordinated, asynchronous contraction of the ventricular muscle fibers of the heart that leads quickly to death from lack of oxygen to the brain. Ventricular fibrillation is terminated by the use of a defibrillator, which provides a pulse shock to the chest to restore the heart rhythm. Cardiopulmonary resuscitation (CPR) is used as a temporary care measure to provide the circulation of some oxygenated blood to the brain until a defibrillator can be used.²³

The speed with which resuscitative measures are initiated has been found to be critical. Immediate defibrillation would be ideal; however, for victims of cardiopulmonary arrest, resuscitation has the greatest rate of success if CPR is initiated within 4 minutes and advanced cardiac life support is initiated within 8 minutes (National Conference on CPR and ECC, 1986).⁶

The presence of moisture from environmental conditions such as standing water, wet clothing, high humidity, or perspiration increases the possibility of a low-voltage electrocution. The level of current passing through the human body is directly related to the resistance of its path through the body. Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms. The following illustrations of Ohm's law demonstrates how moisture affects low-voltage electrocutions. Under dry conditions, Current=Volts/Ohms = 120/100,000 = 1 mA, a barely perceptible level of current. Under wet conditions, Current=Volts/Ohms = 120/1,000 = 120 mA, sufficient current to cause ventricular fibrillation. Wet conditions are common during low-voltage electrocutions.

High-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms. Once the skin is punctured, the lowered resistance results in massive current flow, measured in Amps. Again, Ohm's law is used to demonstrate the action. For example, at 1,000 volts,

Current=Volts/Ohms = 1000/500 = 2 Amps

which can cause cardiac standstill and serious damage to internal organs.

CONCLUSIONS

Electrical hazards represent a serious, widespread occupational danger; practically all members of the workforce are exposed to electrical energy during the performance of their daily duties, and electrocutions occur to workers in various job categories. Many workers are unaware of the potential electrical hazards present in their work environment, which makes them more vulnerable to the danger of electrocution.

The Occupational Safety and Health Administration (OSHA) addresses electrical safety in Subpart S 29 CFR 1910.302 through 1910.399 of the General Industry Safety and Health Standards.³ The standards contain requirements that apply to all electrical installations and utilization equipment, regardless of when they were designed or installed. Subpart K of 29 CFR 1926.402 through 1926.408 of the OSHA Construction Safety and Health Standards⁴ contain installation safety requirements for electrical equipment and installations used to provide electric power and light at the jobsite. These sections apply to both temporary and permanent installations used on the jobsite.

Additionally, the National Electrical Code (NEC)⁵ and the National Electrical Safety Code (NESC)⁶ comprehensively address electrical safety regulations. The purpose of the NEC is the practical safeguarding of persons and property from hazards arising from the use of electricity. The NEC contains provisions considered necessary for safety and applies to the installation of electric conductors and equipment within or on public or private buildings or other structures, including mobile homes, recreational vehicles, and floating buildings; and other premises such as yards; carnival, parking, and other lots; and industrial substations. The NEC serves as the basis for electrical building codes across the United States.

The NESC contains rules necessary for the practical safeguarding of persons during the installation, operation, or maintenance of electric supply and communication lines and associated equipment. These rules contain the basic provisions that are considered necessary for the safety of employees and the public under the specified conditions. Unlike the NEC, the NESC contains work rules in addition to installation requirements.

EPIDEMIOLOGY OF ELECTROCUTION FATALITIES

Suzanne Kisner, B.S., Virgil Casini, B.S.

Occupational fatalities associated with electrocutions are a significant, ongoing problem. Data from the NIOSH National Traumatic Occupational Fatality (NTOF) surveillance system indicated that an average of 6,359 traumatic work-related deaths occurred each year in the United States from 1980 through 1989; an estimated 7% of these fatalities were due to electrocutions.¹² In 1995, the Bureau of Labor Statistics reported that electrocutions accounted for 6% of all worker deaths.¹³ For the year 1990, the National Safety Council reported that electrocutions were the fourth leading cause of work-related traumatic death.¹⁴

A review of hazards in the farming industry showed that electrocutions accounted for about 7% of all agricultural work-related deaths.¹⁵ The specific hazards involved in these electrocutions include internal wiring in farm buildings, buried electrical cables, and overhead powerlines.¹⁵ A study of work-related electrocution deaths was conducted using data from the Occupational Safety and Health Administration (OSHA) Integrated Management Information System (IMIS).¹⁶ This study identified 944 work-related electrocutions for the period 1984 to 1986; 61% of these fatalities were caused by contact with high-voltage powerlines. From 1980 through 1989, NIOSH reported an average of 15 electrocutions each year were caused by contact between cranes or some other type of boomed vehicles and energized, overhead powerlines.¹⁷

NTOF ANALYSIS

Methods

The National Traumatic Occupational Fatalities (NTOF) surveillance system is composed of information taken from death certificates for decedents 16 years of age or older with a positive response to the "Injury at Work?" item, and an external cause of death (International Classification of Diseases, Ninth Revision [ICD-9]; E800-E999).¹⁸ Electrocutions which occurred from 1980 through 1992 were identified by selecting those cases which had an ICD-9 code of "E925-accident caused by electrical current."

An initial manual review identified certain events that occurred with greater frequency. Based on this review, 17% of the cases with specific circumstances were grouped through keyword searches of the literal information from the death certificates. A keyword search was done for "crane," "boom," "hoist," and "rigging" to identify electrocutions involving boomed vehicles. Electrocutions involving ladders and scaffolds were identified through a search for "ladders" and "scaffolds." A keyword search was conducted for "short cir," "faulty," "shorted," "defective," "malfunctioning," "short," and "damaged," to identify those electrocutions involving contact with a short-circuited, damaged, or improperly installed wire or equipment. Contacts with a truck or other vehicle were located using the keywords "truck" and "vehicle." Electrocutions involving grain augers and elevators were found through a search for "auger" and "elevator." Because of the level of detail contained on death certificates, specific circumstances surrounding most of the deaths were not as easily categorized. For most of the remaining cases, the circumstances surrounding the electrocutions were missing, incomplete, or vague. While these cases were not removed from the analysis, to assign them to specific groups would involve a much more detailed review, which is not possible with death certificate data alone.

Industry was coded into division-level industry categories using the 1987 Standard Industrial Classification System.¹⁹ Occupation was grouped into major occupation divisions according to the 1980 and 1990 Bureau of the Census Occupational Classification System.^20,21 Employment estimates used to calculate fatality rates were extracted from the Bureau of Labor Statistics' Employment and Earnings annual average employment data.²² The employment data from Employment and Earnings are based on the annual averages from the Current Population Survey, a sample survey of the population 16 years of age and over.

A detailed description and the limitations of the NTOF surveillance system have been reported previously.¹² Because the amount of detail on death certificates is sometimes limited and death certificates are known to capture approximately 81% of all work-related deaths,²³ the number of electrocutions presented should be considered the minimum number of deaths.

Results

A total of 5,348 workers were electrocuted in 5,180 incidents from 1980 through 1992. One-hundred fifty-three (3%) of the fatal incidents resulted in multiple fatalities: 140 incidents involved 2 victims each, 11 incidents involved 3 victims each, and 2 incidents involved 4 victims each.

An average of 411 workers were electrocuted each year, with an average annual rate of 0.4 per 100,000 workers. Figure 1 provides the frequency and rate per 100,000 workers of electrocutions by year of death. The substantial decrease is noteworthy, but it varies by industry. While total work-related fatalities decreased 23% from 1980 to 1989,²⁴ the number of electrocution deaths have decreased by more than 50% from 1980 to 1992.

Figure 1. Frequencies and Rates of Electrocution Deaths Identified by NTOF by Year, 1980-1992

Sixty percent of the electrocutions occurred to workers less than 35 years of age. Figure 2 provides frequencies and rates per 100,000 workers of electrocutions by age group.

Ninety-nine percent of the electrocutions occurred among men. Whites accounted for 86% of the electrocutions, followed by Blacks (7.1%), Hispanics (5.3%), Asians (0.4%), Native Americans (0.3%), and other and unknown races (0.8%).

Figure 2. Frequencies and Rates of Electrocution Deaths Identified by NTOF by Age Group, 1980-1992

The industries with the highest percentage of electrocutions were construction (40%), transportation/communication/public utilities (16%), manufacturing (12%), and agriculture/forestry/fishing (11%) (Figure 3). The construction industry had a rate of 2.4 per 100,000 workers, followed closely by mining which had a rate of 2.2 (Figure 3).

Over the 13-year period, 61% of the electrocutions occurred in two occupation divisions: 46% among craftsmen and 15% among laborers (Figure 4). These two groups also had the highest rates of electrocution death: 1.4 per 100,000 workers each (Figure 4).

Much of the information from death certificates for decedents involved in electrocutions is vague. However, certain circumstances were easily identifiable. Three-hundred thirty-seven (6%) of the victims contacted a boomed vehicle that was in contact with an energized power source. Two-hundred seventeen (4%) contacted a ladder or scaffold that was in contact with an energized power source. One-hundred fifty-three (3%) contacted short-circuited, damaged, or improperly installed wire or equipment. One-hundred twenty-nine (2%) contacted a truck or other vehicle, other than a boomed vehicle, which was in contact with an energized power source. Eighty-two (2%) contacted an energized grain auger or grain elevator. As previously described, the specific circumstances surrounding the electrocutions in the remaining 83% of the deaths were not categorized in these data.

Figure 3. Frequencies and Rates of Electrocution Deaths Identified by NTOF by Industry, 1980-1992

Figure 4. Frequencies and Rates of Electrocution Deaths Identified by NTOF  by Occupation, 1980-1992

FATALITY ASSESSMENT AND CONTROL EVALUATION (FACE) INVESTIGATIONS

Methods

During the period from November 1982 to December 1994, NIOSH investigated 224 electrocution incidents resulting in 244 occupational fatalities.²⁵ These investigations were undertaken as part of the Fatality Assessment and Control Evaluation (FACE) program conducted by (NIOSH). The FACE program was initiated in 1982 and directed from its inception by the NIOSH Division of Safety Research. FACE is a research program for the identification and investigation of fatal occupational injuries.

Derived from the research conducted by William Haddon, Jr. (the Haddon model), this approach reflects the public health perception that the etiology of injuries is multifactorial and largely preventable.²⁶ For each case, factors associated with the agent (mode of energy exchange), the host (the worker who died) and the environment are identified during the pre-event, event, and post-event time phases. These contributory factors are investigated in detail in each FACE incident, and are summarized in each FACE summary report, along with recommendations for preventing future incidents of a similar nature.

Investigators conducted investigations at the incident sites, evaluating each event's circumstances, including agent, host, and environmental characteristics. When an incident involved multiple fatalities, data were collected for each victim. Percentages presented here describe frequencies of incident characteristics. Rates could not be calculated due to the lack of comparable denominator data. Percentages do not necessarily reflect the risk to workers, but rather describe the problem's proportional magnitude.

Industry was coded into categories using the 1987 Standard Industrial Classification System³¹ and occupations were grouped using the 1980 Bureau of the Census Occupational Classification System.³²

Results

The victims (243 men and 1 woman) ranged in age from 17 to 70 years, and the mean age was 34 years. The loss of years of potential life before age 65 was substantial; for the 244 victims discussed in this analysis, the years of potential life lost (YPLL) equaled 7,903 years or an average of 33 years per victim. Sixty-four percent of the victims died prior to age 35 (Figure 5).

The industries with the highest number of electrocutions were Construction (121); followed by Manufacturing (40); Transportation, Communications, Public Utilities (30); and Public Administration (19) (Figure 6).

Figure 7 shows the 10 job classifications (occupations) with the highest number of fatalities. Although utility line workers (linemen) typically receive extensive training in electrical safety and the hazards associated with electrical energy, they had the highest number of fatal injuries. Twenty-six (55%) utility line worker fatalities were due to the failure to utilize required personal protective equipment (gloves, sleeves, mats, blankets, etc.). Laborers, who generally receive little or no electrical training, were the next highest classification.

Figure 5. Frequencies of Electrocution Deaths Identified by FACE by Age Group, 1982-1994

Figure 6. Frequencies of Electrocution Deaths Identified by FACE by Industry, 1982-1994

Figure 7. Frequencies of Electrocution Deaths Identified by FACE by Occupation, 1982-1994

The number of investigated electrocution incidents by month of occurrence are provided in Figure 8. The largest number of incidents occurred in months where weather conditions were most favorable for the highest level of outside activity.

In 79 (35%) of the incidents, no safety program or established, written safe work procedures existed.

Factors common to these incidents included the lack of enforcement of existing employer policies concerning the use of personal protective equipment, and the lack of supervisory intervention when existing safety policies were being violated. Supervision was present at the site in 120 (53%) of the incidents, and 42 victims were supervisors.

Of the 244 victims, 194 (80%) had some type of electrical safety training. On-the-job training, received by 102 victims, was the most common type of training. Thirty-nine victims received no training at all. One hundred (41%) of the victims had been on the job for less than 1 year.

Fifty-one (23%) of the incidents occurred at establishments that employed 500 or more workers. Eighty-five (38%) of the incidents occurred at establishments that employed less than 50 workers.

Two hundred twenty-one (99%) of the incidents involved alternating current (AC). One incident involved direct current (DC). Two incidents involved AC arcs. Of the 221 AC electrocutions, 74 (33%) involved less than 600 volts and 147 (66%) involved 600 volts or more. The number of electrocutions by voltage level is listed in Figures 9 and 10. Forty (54%) of the lower-voltage electrocutions involved household current of 120 to 240 volts. Manufacturing companies accounted for 40 (54%) of the lower-voltage incidents. This is particularly disturbing due to safety features such as electrical safety interlocks, emergency stop devices, and electrical guarding inherently designed into manufacturing equipment.

Of the 147 higher-voltage incidents, 111 (76%) involved distribution voltages (7,200-13,800 volts) and 21 incidents involved transmission voltages (above 13,800 volts). Of the incidents involving at least 7,200 volts, 41 (28%) resulted from contacting an energized powerline with a boomed vehicle. Thirty-five incidents occurred when conductive equipment such as an aluminum ladder or scaffold contacted an energized powerline. The weight of this equipment sometimes required more than one worker to move or position it, resulting in multiple fatalities. Thirteen deaths occurred in six separate incidents when workers erected or moved scaffolds that came in contact with energized, overhead powerlines. Electric powerline line mechanics were victims in 47 (36%) of the incidents involving transmission and distribution voltages.

Almost all American workers are exposed to electrical energy at sometime during their work day, and the same electrical hazards can affect workers in different industries. Based on the analysis of these cases, NIOSH identified five case scenarios that describe the incidents resulting in the 244 fatalities: (1) direct worker contact with an energized powerline (28%); (2) direct worker contact with energized equipment (21%); (3) boomed vehicle contact with an energized powerline (18%); (4) improperly installed or damaged equipment (17%); (5) conductive equipment contact with an energized powerline (16%).

Figure 8. Frequencies of Electrocution Incidents Identified by FACE by Month, 1982-1994

Figure 9. Frequencies of Electrocution Incidents Identified by FACE by High Voltage Level (>600 Volts), 1982-1994

Figure 10. Frequencies of Electrocution Incidents Identified by FACE by Low Voltage Level (<600 Volts), 1982-1994

Scenario 1

Workers in various occupations such as sign technicians, tree trimmers, utility line workers, and telecommunication workers are often exposed to overhead powerlines. These exposures can be greatly reduced by isolating or insulating the energy source from the worker. This can be accomplished by erecting a physical barrier, by insulating the powerline, or by following required clearance distances. More than once during FACE investigations, co-workers interviewed did not know the powerlines posed a hazard, i.e., they thought the powerlines were insulated.

Scenario 2

Direct worker contact with energized equipment can occur in a variety of ways. Maintenance technicians might inadvertently contact overhead crane runway conductors. Electricians or technicians troubleshooting or testing electric circuitry might contact an energized circuit. Maintenance workers may fail to replace an isolating plate covering electrical conductors, exposing passing workers. Compliance with the applicable articles of the National Electrical Code and lockout/tagout procedures established by OSHA could eliminate the potential for such contact, thereby reducing the risk of electrocution.

Scenario 3

Workers guiding suspended loads, or standing against or near a crane or other boomed vehicle—such as a concrete pumping truck, or derrick truck—whose boom contacts a powerline are in danger of electrocution. The risk of electrocution could be reduced if OSHA regulations regarding clearance distances [(29 CFR 1926.550 (a)(15)] are observed, or if the required lookout person [29 CFR 1926.550 (a)(15)(iv)] is utilized.

Scenario 4

Improperly installed or damaged equipment can be responsible for occupational electrocutions in a variety of ways. The most frequently cited OSHA electrical regulation is improper grounding of equipment or electrical circuitry. If the frame of a piece of electrical equipment or machinery does not have a grounding conductor attaching the frame to ground, as required to divert dangerous fault current to ground, and an electrical fault occurs, anyone touching that frame and any other object at ground potential would receive an electrical shock. Should a fault occur with a grounding conductor present, the circuit would open or trip as an alert that a problem existed, except in high-resistance grounding applications. Damaged guards can expose workers to energized conductors in proximity to their work areas. Additionally, damaged extension cords or extension cords with their ground prong removed can expose workers to the danger of electrocution.

Failure to maintain a continuous path to ground can expose entire electrical systems to damage and can expose the structures within which they are housed and workers within these structures to electrical and fire hazards.

For example, many electrical systems are installed in a manner that allows a structure's water pipes or other conductive conduit to serve as a continuous path to ground in compliance with the NEC. However, FACE investigations have identified cases of electrocution or fire as a result of an interruption in a continuous path to ground. During renovation or repair activities, conductive components may be replaced by nonconductive components such as PVC pipe, which will interrupt the path to ground. This may result in fire due to the intense overheating of components of the electrical system. Additionally, workers contacting improperly grounded components while being at ground potential would be exposed to electric shock.

Scenario 5

The task of positioning or repositioning conductive equipment may place more than one worker at risk. The weight of mobile scaffolding, grain augers, or aluminum extension ladders equipped with pendant-operated lifts often requires more than one worker for positioning or repositioning, resulting in multiple electrocutions if contact with an overhead powerline occurs. Using a lookout person, observing required clearance distances, or lowering this equipment before transport would greatly reduce worker exposure to any potential electrical hazards present.

DISCUSSION

The fatality data from NTOF help to illustrate the magnitude of the electrocution problem nationally and allow a comparison of the potential risks in various industries. The information from FACE investigations allows for the identification of more detailed information on electrocution hazards, such as contact with overhead powerlines, contact with exposed conductors, inadequate personal protective equipment, and nonexistent lockout/tagout procedures, or other measures necessary for working around energized conductors and equipment.

FACE reports and NTOF death certificates identified many of the same hazards for fatal electrocutions. The largest number of deaths were in Construction, Transportation/Communication/Public Utilities, and Manufacturing, while the highest fatality rates were in the Construction and Mining industries. Linemen were involved in the largest number of electrocutions.

Direct worker contact with an energized powerline caused the largest number of electrocution deaths. Almost all of the incidents investigated by FACE involved alternating current. Over half of these incidents involved voltages over 600 volts. Of the 147 higher-voltage electrocutions, over two-thirds involved distribution voltages (7,200-13,800 volts).

While progress has been made in reducing the number of work-related electrocutions, (50% decrease from 1980-1992), additional efforts are needed if we are to continue progress towards preventing deaths due to electrocution.

PUBLIC HEALTH SUMMARY

What are the hazards?

Based on data from the NIOSH National Traumatic Occupational Fatalities (NTOF) surveillance system, electrocutions were the fifth leading cause of death from 1980 through 1992. The 5,348 deaths caused by electrocutions accounted for 7% of all fatalities and an average of 411 deaths per year.

How can a worker be exposed or put at risk?

Electricity is present at most jobsites, and many American workers, regardless of industry or occupation, are exposed to electrical energy daily during the performance of their tasks. These hazardous exposures may exist through contact with an object as seemingly innocuous as a broken light bulb to an energized overhead powerline.

What recommendations has the federal government made to protect workers' health?

The Occupational Safety and Health Administration (OSHA) addresses electrical safety in Subpart S 29 CFR 1910.302 through 1910.399 of the General Industry Safety and Health Standards. The standards contain requirements that apply to all electrical installations and utilization equipment, regardless of when they were designed or installed. Subpart K of 29 CFR 1926.402 through 1926.408 of the OSHA construction safety and health standards contain installation safety requirements for electrical equipment and installations used to provide electric power and light at the jobsite. These sections apply to both temporary and permanent installations used on the jobsite. Additionally, the National Electrical Code (NEC) and the National Electrical Safety Code (NESC) comprehensively address electrical safety regulations. NIOSH recommendations focusing on prevention are included in this Technical Document.

MORE

Have fun. That is the goal of many of the offerings here at ElectricianEducation.com.