10166396444143Trans Soc Min Metall Explor IncTrans Soc Min Metall Explor IncTransactions of Society for Mining, Metallurgy, and Exploration, Inc1075-8623263460414558412HHSPA707258ArticleElectrical injuries in the US mining industry, 2000-2009HomceG.T.Lead electrical engineer, National Institute for Occupational Safety and Health, Office of Mine Safety and Health Research, Pittsburgh, PACawleyJ.C.Electrical safety consultant, McDonald, PA12820152013039201534367375

The U.S. National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) conducted a study of mining industry electrical injuries reported to the U.S. Mine Safety and Health Administration (MSHA) for the years 2000 to 2009. The findings of that study are detailed in this paper, and serve to characterize the circumstances surrounding electrical injuries and identify causal factors. The study included three tasks: 1) a direct review of mining industry occupational injury data compiled by MSHA, 2) interpretation of the narrative descriptions available for the injuries (from MSHA data) and 3) a separate examination of fatal electrical injuries. Eight-hundred sixty-five electrical injuries were reported during the 10-year period studied, with 39 of those being fatalities. This makes electrical injuries disproportionately fatal with respect to most other types of injuries in mining. Electrical injury rates were higher in coal mining than noncoal mining and, within the coal sector, rates were higher in underground operations than in surface operations. Of the 865 total cases, electrical and machine maintenance or repair activities were involved in 580 (69%), and electricians and mechanics were injured in 362 cases (42%). Of the 39 fatal electrical injuries, 27 (69%) involved electrical maintenance or repair work, and in 21 of these 27 cases, the failure to de-energize, lock-out and tag the circuit was the cause or a contributing factor. Also, contractor employees had a much greater chance of an electrical injury being fatal than did mine operator employees. The top three root causes for fatal electrical injuries were 1) no or inadequate lock-out and tagging, 2) failure of power system components and 3) contact of overhead electrical power lines by mobile equipment.

Health and safetyElectrical injuriesMSHAIntroduction

Electrical accidents cause a large number of serious occupational injuries each year. The U.S. Bureau of Labor Statistics (BLS) data indicate that 1,573 workplace fatalities in the United States between 2003 and 2009 had an electrical cause, and an estimated 18,260 nonfatal electrical injuries, resulting in days away from work, occurred over the same period.1 The electrical fatality rate for the composite of all U.S. industries averaged 0.16 deaths per 100,000 workers (annually) for 2003 to 2009.2 Electrical fatality rates can be much higher for specific industries, however, with BLS data reporting an average rate of 1.06 for the construction industry, 1.33 for the utility sector and 1.15 for the mining industry for the same period (Cawley, 2011).

Accident data compiled by the U.S. Mine Safety and Health Administration (MSHA) corroborate BLS electrical fatality statistics, revealing electrical fatality rates for the mining industry averaging 1.36 deaths per 100,000 workers for 2003 through 2009. These statistics show mining to be among the most dangerous industries with respect to electrical hazards, and suggest a need to clearly characterize the circumstances surrounding electrical injuries and identify causal factors. With this purpose, the U.S. National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) conducted a study of mining industry electrical injuries reported to MSHA for the years 2000 to 2009. The findings of that study are detailed in this report. The most recent comprehensive NIOSH study of mining electrical accidents and injuries covered the years 1990 to 1999 (Cawley, 2003).

Presented first is a brief explanation of the data used, including their source, processing and limitations. Next are the results of the study, including 1) a detailed review of information available directly from MSHA data, 2) interpretation of the narrative descriptions supplied for each accident and 3) a separate examination of fatal electrical injuries. Finally, key points and conclusions from the study are summarized.

Data used for the study

Per provisions of the Federal Mine Safety and Health Act of 1977, MSHA collects and maintains information on accidents, injuries and illnesses occurring at mining operations, as well as information on mines, employment and production, for mine operators and mining contractors.3 Most of the analyses described in this report used MSHA Accident, Injury and Illness (AI) data for the years 2000 through 2009.4 Injury rate calculations also used mining industry employment numbers for 2000 to 2009 taken directly from MSHA mining industry data summary tables and annual reports.5 In addition, most of the information used in the analysis of fatal electrical injuries came directly from MSHA fatal accident investigation reports.6 All data include mine operator employees and contractor employees unless otherwise noted.

MSHA AI data include a variable designated as Accident, Injury, Illness (variable name aii), which is a descriptor that most closely identifies the overall cause of an accident. This study included all reported cases with injuries having the cause (aii) listed as Electrical. In a wider review of the AI data, 12 other injuries for which the actual cause appeared to be electrical were found classified under cause categories other than Electrical, and these were added to the cases to be studied. These 12 additional injuries were found by identifying cases for which the MSHA accident type (variable name atype) was listed as Flash Burn, and/or the MSHA nature of injury (variable name natinj) was listed as Electrical burn, Noncontact electrical burn or Electrical shock/electrocution, but the cause was not listed as Electrical. Except where noted, the more complete set including these 12 extra cases was used throughout this study.

MSHA AI raw data contain not only entries for accidents that resulted in an occupational injury, but also numerous accidents that did not result in an injury. This is due to the statutory requirement for mines to report certain potentially hazardous events to MSHA, irrespective of whether any injuries occurred, such as unplanned gas or dust explosions, unplanned liquid or gas inundations, unplanned underground fires not extinguished within 10 minutes of discovery and certain types of roof falls and coal or rock outbursts. Such cases (not resulting in an injury) listing the cause as Electrical were found to yield little insight into electrical shock or burn hazards and, thus, were not included in the analyses for this study.7

Study resultsOverview of electrical injuries in mining

There were 125,594 mining injuries reported to MSHA for 2000 through 2009, and Electrical was the 10th most frequently listed cause, with 853 injuries. For comparison, the three most frequent causes of all mining injuries were Handling material at 42,426 cases, Slip or fall of person at 25,141, and Machinery at 16,556. Table 1 lists the number of injuries reported for all causes.

Of the 125,594 total mining injuries between 2000 and 2009, 620 were fatalities. Of the 853 mining electrical injuries for that period (those with the cause listed as Electrical), 39 were fatal, making electrical injuries the 6th most prevalent cause of death in mining. For comparison, the two leading causes of fatal injuries for the same period were Powered haulage with 186 cases, and Machinery with 123. Electrical fatalities were nearly as common as fatalities due to Ignition or explosion of gas or dust for the same period. Table 2 lists all mining fatalities by cause.

Although the total number of electrical injuries in mining was comparatively low for the period under study (10th highest among all injury causes, as shown in Table 1), electrical injuries were disproportionately fatal, with one death for every 21.9 injuries. Based on this parameter (the average number of injuries resulting in one fatality), Electrical was the fourth most deadly cause of injury in mining, 9.3 times higher than the composite average for all types of mining injuries for the period (one fatality for every 202.6 injuries). Table 3 lists the six most disproportionately fatal injury causes.

Electrical injury rates in the U.S mining industry for 2000 through 2009 exhibit some annual variation, but suggest an overall decline. For comparison, rates for all types of injuries in mining (not only electrical) were examined, and show that the drop in electrical injury rates was similar to a downward trend in rates for the composite of all injuries in mining over that period.8 Figure 1 compares trends in electrical injury rates and all injury rates in mining for 2000 to 2009.

Analysis of selected MSHA AI data variables for electrical injuries

MSHA data report 865 electrical injuries at U.S. mining operations for 2000 to 2009, including 853 with aii listed as Electrical, and 12 additional cases with apparent electrical causes for which aii was classified as something other than Electrical. The following is a summary of findings from analyses of selected MSHA AI data variables for these electrical injuries, including details on mining industry sector, general location at the mining operation, job title and activity of the injured worker, and the nature and degree of injury.

MSHA data identify a general commodity class (variable name canvass) for the facility associated with each incident. Table 4 shows the number of electrical injuries that occurred under each general commodity class, with Bituminous coal, Stone and Sand and gravel having the most incidents. The latter two include aggregate material operations. Figure 2 shows that electrical injury rates for coal mining were higher than for noncoal from 2000 to 2009.9

MSHA data identify the general location at a mining operation at which each reported incident occurred (variable name subunit). Table 5 lists the number of electrical injuries that occurred at each of several different general locations. Focusing specifically on the coal mining sector, Fig. 3 shows that coal mine underground operations had significantly higher electrical injury rates than coal mine surface operations for 2000 to 2009.

Two other important aspects of electrical injuries are the regular job title of the worker involved (MSHA data variable jobtitl2 was used for this study) and the worker's activity when injured (MSHA variable mwactiv). Not surprisingly, for electrical injuries, Electrician/helper/wireman and Mechanic/repairmen/helper were the two most common regular job title categories cited, and Electrical maintenance/repair and Machine maintenance/repair were the most common activities. Tables 6 and 7 provide more detail for regular job titles and worker activities associated with electrical injuries.

Although shock is the injury often associated with electrical accidents, for this study period burns were far more common nonfatal electrical injuries in mining, including tissue damage due to current flow through the body and burns from radiant energy. In comparison, electrical fatalities were nearly always due to shock. Table 8a lists the seven most common nature of injury categories (MSHA variable natinj) for coal mining injuries with the cause listed as Electrical, as well as the number of incidents and lost workday data for each. Table 8b provides the same information for noncoal operations. Table 9 further characterizes mining electrical injuries by listing the number of incidents for various degrees of injury categories (MSHA variable deginj).

Mine operators are required to report to MSHA accidents occurring on their property and involving operator employees and contract employees. During the 2000 to 2009 period, 733 mining electrical injuries involved operator employees and 132 involved contractors. Based on the average number of electrical injuries resulting in one fatality, contractors tended to have a higher proportion of fatal electrical injuries than operator employees, as shown in Table 10.

Analysis of MSHA AI data narrative descriptions

MSHA AI database information includes a narrative description of each reported accident. Although the clarity and level of detail for these descriptions can vary widely, they are overall a valuable source of additional information about the circumstances surrounding electrical injuries, providing insight into how and why the associated accidents occurred. The narratives for the 865 mining electrical injuries occurring between 2000 and 2009 were reviewed and analyzed, with information extracted that was not available in the other MSHA data variables. The scope and content of this analysis was dictated primarily by the detail available in the narratives, rather than by any preset structure.

Based on this narrative review, Table 11 lists the frequency with which several selected causal factors were involved in electrical injuries. Note that for each causal factor listed in Table 11, not all 865 narrative descriptions provided enough information to determine if the factor was or was not involved. Therefore, the actual number of cases on which each evaluation was based is noted. For the causal factor Personal protective equipment (PPE) would have prevented the injury or reduced its severity, such PPE would include not only electrically rated gloves and arc-rated clothing/equipment for electricians, but also nonelectrical-specific equipment such as leather work gloves to prevent burns while operating breakers or handling cables. Also, for each injury, a specific power system component or piece of equipment was identified as having played a primary role. The most commonly involved power system components/equipment are listed in Table 12.

Further analysis of the findings in Table 12 ultimately identified five general categories of components and equipment most often involved in mining electrical injuries, as listed below.

Electrical switchgear – 24.6% of 856 cases reviewed; combines the categories Circuit breakers, Switches and Line starters.

45% of injuries occurred at stone mines and 34% at coal mines.

59% of injuries occurred during maintenance and 36% during normal operation of devices.

Approximately 68% of injuries were noncontact electrical burns due to arcing.

Trailing cables - 8.9% of 856 cases reviewed.

91% of injuries occurred at coal mines, primarily involving mobile underground equipment trailing cables.

71% of injuries occurred while personnel were handling cables (not during repair activities) and 16% occurred during cable repair.

54% of injuries were electrical shocks, 24% were noncontact electrical burns and 17% were electrical burns.

Underground mine mobile-equipment batteries - 7.5% of 856 cases reviewed; includes approximately one-third of the cases in the Battery category in Table 12, as well as selected relevant cases from the categories Underground battery-powered equipment (not shown in Table 12) and Cable coupler or plug.

All injuries occurred at coal mines.

Most injuries involved support equipment such as scoops, mantrips and locomotives.

Injuries usually occurred during maintenance or battery changes.

Injuries were often noncontact electrical burns due to arcing.

Cable couplers or plugs — 6.9% of 856 cases reviewed.

90% of injuries occurred in coal mines.

47% of injuries occurred during insertion or removal, 29% during repair of the coupler or plug and 24% while energizing the associated circuit.

59% of injuries involved ac circuits, primarily on power centers (balance of injuries involved dc circuits).

73% of injuries were noncontact electrical burns due to arcing.

Engine-starter batteries on surface equipment or vehicles - 6% of 856 cases reviewed; includes approximately one-half of the cases in the Battery category in Table 12.

Injuries occurred at coal and noncoal operations, typically involving large off-road equipment.

Injuries occurred during battery maintenance or while using battery booster cables to start equipment.

Injuries were primarily chemical burns due to battery ruptures or explosions, and noncontact electrical burns due to arcing.

Analysis of fatal electrical injuries

As noted previously, electrical injuries, although the 10th most common type of injury in mining (Table 1), rank fourth with respect to the average number of injuries resulting in one fatality (Table 3). Therefore, the 39 electrical fatalities occurring between 2000 and 2009 were examined more closely in this study, by reviewing the detailed fatal accident investigation reports produced by MSHA. These reports were analyzed, and information was compiled about how and why the deaths occurred. Table 13 lists the types of mining operations, by mined commodity, at which the fatal injuries occurred, and Table 14 categorizes the fatalities by the circumstances surrounding the associated accident. The most common circumstance was electrical maintenance and repair work, accounting for 27 deaths, and this category is detailed further in Table 15.

One frequent cause or contributing factor in electrical accidents is the failure to create an electrically safe work condition, or more specifically, failure to effectively de-energize, lock out and tag the circuit in question. In 21 of the 27 Electrical maintenance or repair fatal injuries detailed above, the circuits could have and should have been put in an electrically safe work condition. Although for most of the 21 cases in question, it is difficult to determine exactly why the circuit involved was not de-energized, a number of key factors seem to be common in the accidents, such as existence of an unrecognized problem or abnormal condition on the power system, unfamiliarity with the power system or a component, lack of adequate focus by the worker on the task involved, failure to use appropriate personal protective equipment (PPE) and unsafe work procedures. Interestingly, although diagnosing a power system problem is often cited as a circumstance where working on an energized circuit is necessary and allowable, six of the eight Diagnostic work (troubleshooting) fatalities cited above involved situations where the circuits involved could have been de-energized without hampering the work. Such cases included removing power fuses for testing, examining malfunctioning mechanical components in a high voltage switch cabinet, disconnecting a malfunctioning control circuit connection and using temporary power connections instead of appropriate instruments for motor and cable testing.

Another analysis approach used to study the MSHA electrical fatality investigation reports was an attempt to determine a root cause for each incident. A root cause can be defined as the basic lowest-level causal factor for an event, with the event in this case being a fatal electrical accident (Ericson, 2005). The factor can be any hazardous element, such as a component, a system condition or an activity and, in this analysis, the root cause would best be described as the element that played the most important role in the chain of events leading up to the incident. As such, the root causes identified are not necessarily the last or most obvious elements involved in each case, and certainly they are usually accompanied by several contributing factors. The root causes identified for the 39 mining electrical fatalities are summarized under several general categories in Table 16.

Summary

A study of electrical injuries occurring in the U.S mining industry between 2000 and 2009 was conducted by NIOSH to characterize the circumstances surrounding electrical injuries and identify causal factors. A total of 865 electrical injuries were reported to MSHA for this period, 39 of which were fatal. Of the total 865 electrical injuries, approximately 42% were noncontact electrical burns (due to arcing), 26% were electrical shocks and 13% were contact electrical burns (due to current flow through tissue). A summary of other important findings follows.

Electrical accidents were the 10th most common cause of injuries in mining, the sixth most common cause of fatal injuries and ranked fourth with respect to lethality (measured as the average number of injuries (fatal and nonfatal) resulting in one fatality).

Electrical injury rates for mining generally declined between 2000 and 2009, as did the composite rates for all types of injuries in mining over that period.

The bituminous coal sector accounted for 47% of electrical injuries, and had a higher electrical injury rate than noncoal mining.

In the bituminous coal sector, electrical injury rates for underground operations were notably higher than those for surface operations.

Electricians and mechanics accounted for 42% of electrical injuries.

Electrical and machine maintenance/repair activities were involved in 69% of electrical injuries.

Contractor employees tended to have a higher proportion of fatal electrical injuries than did mine employees.

Improper work procedures caused or helped cause 88% of electrical injuries.

The use of PPE would have prevented the injury or lessened its severity in 69% of cases.

The most common power system components or equipment involved in accidents resulting in electrical injuries were 1) electrical switchgear, 2) trailing cables, 3) batteries used in battery-powered underground mobile equipment, 4) power cable plugs and couplers and 5) surface equipment engine-starter batteries.

Of 39 total fatal electrical injuries, 21 occurred in coal mining, with 12 in underground operations and nine at surface operations.

Of 39 total fatal electrical injuries, 27 involved electrical maintenance or repair work, and in 21 of these 27, circuits should have been de-energized, locked out and tagged prior to work.

The top three root causes for fatal electrical injuries were 1) no or inadequate lock out and tagging, 2) failure of power system components and 3) contact of overhead electrical power lines by mobile equipment.

BLS occupational injury data is compiled differently than the accident and injury data collected and maintained by MSHA. For more information on BLS occupational injury data, see http://www.bls.gov/iif/.

Analysis of injury frequencies, that is, the actual number of injuries over a period of time, is useful for characterizing the nature and impact of safety hazards, as when comparing injury causes or severity; however, frequencies are usually not appropriate for comparing injury records among different exposed populations or for identifying trends, because they do not account for differences in workforce size. Rates of injury normalize data and, therefore, afford a means to directly compare the safety experience of different size groups, or study changes over time for a specific group. Typically, rates are calculated as the number of injuries per some standard population size over a one-year period. This paper presents both injury frequencies and rates as appropriate.

See http://www.msha.gov/30cfr/50.0.htm and http://www.msha.gov/30cfr/45.0.htm for more information.

MSHA AI raw data files are available at http://www.msha.gov/STATS/PART50/p50y2k/p50y2k.HTM, and MSHA data files converted to SPSS and dBase IV formats by NIOSH are available at http://www.cdc.gov/niosh/mining/data/default.html.

Historical mining industry employment data are available at http://www.msha.gov/ACCINJ/accinj.htm.

MSHA mining fatal accident investigation reports are available at http://www.msha.gov/fatals/fab.htm.

MSHA AI data include a variable called degree of injury (deginj) for each accident. The degree of injury categories that represent no injury or a noncountable injury, and so were excluded for this study, were: no injury, occupational illness, employee natural cause fatal and nonfatal injury, and nonemployee fatal and nonfatal injury (in the last category, nonemployee means a person other than 1) an employee of the mine operator or 2) a contractor employee working on mine property).

Injury rates presented in this paper are for fatal and nonfatal injuries combined, per 100 full-time equivalent employees annually, calculated as: Injury rate = [(number of injuries for target year) ÷ (total hours worked by exposed employees)] × [200,000]. Electrical injury totals used to calculate electrical injury rates include only the injuries reported to MSHA for which the cause (aii) was listed as Electrical. All rates were calculated excluding office workers from the exposed populations, and assuming 2,000 hours worked annually per employee.

Rates cannot be calculated for general commodity classes (canvass) because contractor hours worked are reported to MSHA identified only as coal or noncoal locations.

ReferencesCawleyJCElectrical accidents in the mining industry, 1990-1999IEEE Transactions on Industry ApplicationsNov-Dec200339615701577CawleyJCESFI White Paper - Occupational Electrical Accidents in the U.S., 2003-20092011http://esfi.org/index.cfm/page/ESFI-White-Paper-Occupational-Electrical-Accidents-in-the-U.S.,-2003-2009/cdid/11510/pid/10272EricsonCAHazard Analysis Techniques for System Safety2005II478Wiley Interscience

Rates for all types of injuries in mining and for electrical injuries in mining, for 2000-2009.

Electrical injury rates for coal mining and noncoal mining, for 2000-2009.

Electrical injury rates for underground and surface operations of coal mines, for 2000-2009. Underground and surface locations are defined based on MSHA general location (subunit) categories. Surface operations include all general location categories except underground operations of underground mines.

Injuries reported to MSHA for 2000-2009, listed by cause (aii).

Cause of injury (aii)Fatal and nonfatal injuries
Handling material42,426
Slip or fall of person (from an elevation or on the same level)25,141
Machinery16,556
Hand tools15,880
Powered haulage11,272
Fall of roof, back or brow (from in place)3,991
Stepping or kneeling on object1,952
Striking or bumping1,243
Fall of face, rib, pillar, side or highwall (from in place)1,147
Electrical853
Exploding vessels under pressure491
Falling, rolling or sliding rock or material of any kind474
Nonpowered haulage357
Fire250
Ignition or explosion of gas or dust185
Hoisting135
Explosives and breaking agents76
Inundation7
Entrapment5
Disorders associated with repeated trauma2
Dust disease of the lungs1
Other causes not listed as possible aii choices3,150
Total 125,594

Mining fatal injuries reported to MSHA for 2000-2009, listed by cause (aii).

Cause of injury (aii)Fatalities
Powered haulage186
Machinery123
Slip or fall of person (from an elevation or on the same level)62
Fall of roof, back or brow (from in place)58
Ignition or explosion of gas or dusta41
Electrical39
Fall of face, rib, pillar, side or highwall (from in place)31
Falling, rolling or sliding rock or material of any kind29
Exploding vessels under pressure8
Hoisting7
Handling material5
Hand tools3
Fire3
Explosives and breaking agents2
Stepping or kneeling on object1
Other causes (aii) not listed as possible choices21
Total 620

Note that the 41 fatalities from ignition or explosion of gas or dust include 30 deaths from three large accidents—13 at Jim Walters Resources #5 Mine on 9-23-01, 12 at the Sago Mine on 1-2-06, and 5 at Darby Mine #1 on 5-20-06.

Average number of injuries (fatal and nonfatal) resulting in one fatality, for the six most disproportionately fatal injury causes (aii), and for all mining electrical injuries combined, for 2000-2009 mining injuries reported to MSHA.

Cause of injury (aii)Average number of injuries (fatal and nonfatal) resulting in one fatality
Ignition or explosion of gas or dust1 death for every 4.5 injuries
Falling, rolling or sliding rock or material of any kind1 death for every 16.3 injuries
Hoisting1 death for every 19.3 injuries
Electrical1 death for every 21.9 injuries
Fall of face, rib, pillar, side or highwall (from in place)1 death for every 37.0 injuries
Explosives and breaking agents1 death for every 38.0 injuries
Injuries of all types (all aii categories combined) 1 death for every 202.6 injuries

Mining electrical injuries reported to MSHA for 2000-2009, listed by general commodity class (canvass) (N = 865).

General commodity class (canvass)Nonfatal electrical injuriesFatal electrical injuries
Anthracite coal00
Bituminous coal38521
Metal605
Nonmetal451
Sand and gravel1087
Stone2285

Mining electrical injuries reported to MSHA for 2000-2009, listed by general location (subunit) (N = 865).

General location (subunit)Nonfatal electrical injuriesFatal electrical injuries
Underground operations29213
Surface (strip or openpit mines)2629
Mill or preparation plant2137
Surface at underground397
Dredge operations133
Office3
Independent shops and yards2
Auger operations1
Other surface (for metal/nonmetal mines only)1

The 20 most frequently listed regular job title categories (jobtitl2) for electrical injuries reported to MSHA for 2000-2009 (N = 865).

Job title category of injured worker (jobtitl2)Nonfatal electrical injuriesFatal electrical injuries
Electrician/helper/wireman22017
Mechanic/repairman/helper1232
Supervisory/management/foreman/boss11210
Laborer/utility man/bull gang775
Sizing/washing/cleaning plant operator/worker66
Roof bolter (single head)29
Shuttle car/ram operator (standard side)261
Bulldozer/tractor operator201
Truck driver201
Continuous miner operator15
Front-end loader/high lift operator15
Scoop car/tram/load haul dump operator12
Miner NEC/surface miner81
Welder/blacksmith81
Oiler/greaser8
Dragline/crane/backhoe operator7
Engineer (electrical/ventilation/mining)7
Trainee6
Inspector/fire boss/pre-shifter5
Unknown or not elsewhere classified5

The 15 most frequently listed mine worker activities (mwactiv) for electrical injuries reported to MSHA for 2000-2009 (N = 865).

Mine worker activity (mwactiv)Nonfatal electrical injuriesFatal electrical injuries
Electrical maintenance/repair48927
Machine maintenance/repair831
Move power cable49
Handling supplies or material, load and unload422
Inspect equipment293
Hand tools (not powered)12
Welding and cutting122
Idle (eat lunch, coffee break, etc.)8
Observe operations8
Haulage truck6
Get on or off equip. machines, etc.5
Roof bolter, not elsewhere classified5
Surface equipment, not elsewhere classified5
Walking/running5
Conveyor belt (not riding)4

The seven most frequently cited nature of injury (natinj) categories, and lost workday data, for coal mining electrical injuries reported to MSHA for 2000-2009 (N = 406).

Nature of electrical injury (natinj)FatalNonfatalTotal lost workdaysAverage lost workdays per nonfatal injury
Noncontact electric arc burn11583,30121
Electric shock, electrocution19973,29934
Electrical burn1521,59531
Burn, chemical3331410
Burn or scald (heat)171,742102
Multiple injuries626945
Fracture, chip4441110

The seven most frequently cited nature of injury (natinj) categories, and lost workday data, for noncoal mining electrical injuries reported to MSHA for 2000-2009 (N = 459).

Nature of electrical injury (natinj)FatalNonfatalTotal lost workdaysAverage lost workdays per nonfatal injury
Noncontact electric arc burn2054,31721
Electric shock, electrocution17942,54827
Electrical burn5896117
Burn or scald (heat)2368330
Burn, chemical22402
Cut, laceration, puncture9354
Asphyxia, strangulation, drowning, etc.1431

Mining electrical injuries reported to MSHA for 2000-2009, listed by degree of injury (deginj).

Degree of electrical injury (deginj)Number of cases, coalNumber of cases, noncoalNumber of cases, total
Death, fatal211839
Permanent disability, partial or total123
Days away AND restricted activity164460
Days away from work only259203462
Days of restricted activity only174764
Injuries w/o death, days away or restricted activity87132219
All other cases (including first aid)51318
Total406459865

Average number of electrical injuries (fatal and nonfatal) resulting in one fatality listed for coal and noncoal mining by employer type, and for all mining electrical injuries combined, for 2000-2009 mining electrical injuries reported to MSHA.

Industry segment and employerAverage number of electrical injuries (fatal and nonfatal) resulting in 1 fatality
Coal operators1 death for every 23.4 injuries
Coal contractors1 death for every 9.2 injuries
Noncoal operators1 death for every 31.8 injuries
Noncoal contractors1 death for every 12.8 injuries
All mining1 death for every 21.9 injuries

Selected causal factors for accidents resulting in mining electrical injuries, for 2000-2009.

Selected causal factors for accidents resulting in mining electrical injuriesPercent of cases (based on the number of cases out of 865 total injuries, for which enough narrative information is available to make a determination)
Improper work procedures caused or helped cause the accident88% (based on 774 cases)
Personal protective equipment (PPE) would have prevented the injury or reduced its severity69% (based on 777 cases)
The accident involved an arcing fault59% (based on 775 cases)
An electrical system component failure caused the accident49% (based on 655 cases)
Accident involved electrical troubleshooting27% (based on 583 cases)
Accident involved use of a portable electrical meter7% (based on 710 cases)

The 11 most common power system components or pieces of equipment identified as having played primary roles in mining electrical injuries for 2000-2009.

Power system components or equipment involved in mining electrical accidents resulting in injuriesPercent of cases (based on 856 of 865 total injuries)
Circuit breaker14.5%
Battery11.6%
Trailing cable8.9%
Electrical components not elsewhere classified8.1%
Switch7.1%
Cable coupler or plug6.9%
Cable not elsewhere classified6.3%
Fuse or fused disconnect5.0%
Electrical enclosure not elsewhere classified4.1%
Overhead electrical power line3.4%
Line starter3.0%

The categories cited here were derived as needed for analysis of the accident narratives, and are not based on MSHA data variables.

Mining fatal electrical injuries for 2000-2009, listed by type of mining operation (commodity) (N = 39).

Type of mining operation (commodity produced) at which fatal electrical injury occurredNumber of fatal electrical injuries
Coal, bituminous (underground operations)12
Coal, bituminous (surface mines and surface at underground mines)9
Sand and gravel7
Crushed limestone5
Copper2
Gold1
Taconite1
Potash1
Tunneling operation1

Mining fatal electrical injuries for 2000-2009, listed by circumstances of accident causing the electrical fatality (N = 39).

Circumstance of accident causing fatal electrical injuryNumber of fatal electrical injuries
Electrical maintenance or repair work27
Overhead electrical power line contact, not during electrical maintenance or repair work6
Contact with equipment or structures that were energized due to power system damage or disrepair, during activities other than electrical maintenance or repair work4
Welding (contact with welding leads)2

Detail on fatal electrical accidents occurring during electrical maintenance or repair work, for mining fatal electrical injuries 2000-2009 (N = 27).

Specific electrical maintenance or repair work underway when fatal electrical injury occurredNumber of fatal electrical injuries
Repair work11
Diagnostic work (troubleshooting)8
Installing new equipment4
Inspection of equipment2
Operating a cable-fault-locating device1
Unsafe temporary wiring in use1

General categories of root causes for mining fatal electrical injuries for 2000-2009 (N = 39).

General category of root cause identified for mining fatal electrical injuryNumber of fatal electrical injuries
No or inadequate lock-out and tagging procedure used during electrical maintenance or repair work17
Faulty power system components such as damaged power cable or wiring insulation, electrical system components improperly installed or in disrepair, and switchgear not working properly8
Overhead power line contacts by mobile equipment during activities other than overhead power line maintenance or repair5
Unsafe diagnostic procedures (troubleshooting)3
Mobile equipment frames energized after striking and damaging a trailing cable, during equipment operation2
Contact with arc-welding leads2
Inappropriate use of a 480 Vac circuit for explosives initiation1
Improper use of a cable-fault-locating device1