The potential impact of light emitting diode lighting on reducing mining

injuries during operation and maintenance of lighting systems

Michael R. Yenchek *,

* Corresponding author. Tel.: +1 412 386 6099.

E-mail address: mby5@cdc.gov (M.R. Yenchek).

John J. Sammarco

National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, P.O. Box 18070, 626 Cochrans Mill Road, Pittsburgh, PA 15236, USA

abstract

Research by the US National Institute for Occupational Safety and Health (NIOSH) indicates that light

emitting diodes (LEDs) can be used to enhance safety by improving a miner’s ability to see mining hazards and reducing glare. This paper investigates if LEDs provide another benefit by reducing miner exposure to hazards during maintenance and operation of LED lighting. LEDs could provide useful lives up to

50 times longer than incandescent lighting commonly used in mining and could enable design changes to

reduce certain hazards. The mining accident records compiled by the Mine Safety and Health Administration (MSHA) were examined to determine the extent and nature of accidents involving the maintenance

and operation of mine luminaries. A total of 140 relevant accident records were found for the years 2002–

2006. These incidents resulted in 3668 days lost from work with an additional 925 days of restricted

activity. The injury narratives were studied to determine if the implementation of LED-based luminaries

could reduce injury severity and frequency. The greatest near-term potential impacts appear to be related

to reducing maintenance and cap lamp redesign. Longer term (5 years), low-power and lightweight auxiliary LED lighting for surface mines could also have potential impact for improving safety.

1. Introduction

Coal is a vital energy source, with coal-fired electrical generation plants providing about 45% of the electricity for the US. The

importance of mining is even more evident when one considers

that approximately 619,000 people (US Bureau of Labor and Statistics, 2008a) are employed in the mining industry, including those

directly employed by mining companies and those in support-related jobs. The hazardous nature of mining is well-known throughout the world. There has been a declining trend of mining accidents

during the last century; however, recent mining disasters such as

at Sago Mine, West Virginia, quickly remind us of the many dangers encountered by miners.

Miners depend on established safe work practices, safety monitoring systems, safety devices and interlocks, and personal protection equipment to perform their work. Proper lighting plays a

significant role in safety; however, lighting is generally overlooked

as a safety factor and the risks associated with maintaining lighting

systems are often neglected (Driscoll et al., 2007). In underground

mining, the quality and quantity of illumination are important factors for miners to safely perform their jobs (Sanders and Peay,

1988). Miners depend heavily on visual cues to spot fall of ground,

potential machinery-related pinning and striking incidents, and

slipping and tripping hazards (Cornelius et al., 1998). The Illuminating Engineering Society of North America cites the working face

of an underground coal mine as the most difficult environment in

the world to illuminate (Rea, 2000). It is a dynamic environment

that includes dust, confined spaces, low reflective surfaces, low visual contrasts, and glare. This harsh environment poses many hazards encountered during the operation and maintenance of mining

equipment.

Miners wear cap lamps on their hard hats to illuminate nearby

areas where their vision is directed. Underground lighting installed

on mobile machinery is used to illuminate work areas for the machine operators. Headlights are used to improve visibility in the

direction of travel, while flood-type lights provide illumination

around the machine periphery. For surface mining, lights are used

to illuminate mobile surface-mining equipment and the hazardous

areas surrounding this equipment, as well as catwalks, walkways,

loading and dumping sites, and general work areas. Auxiliary light

plants are used to concentrate illumination on specific work areas

of interest, such as the entrances of highwall mines.

Recent safety analyses of mining accidents include a study of

electrical accidents during 1990–1999 (Cawley, 2003), an investigation of work locations (Karra, 2005), a global risk analysis

(Komljenovic et al., 2008), and an analysis of accidents involving

mining equipment (Groves et al., 2007). These prior reports did

not address lighting-related injuries in mining, nor did they address the extent of maintenance or operational-related accidents.

However, other industries have noted maintenance or operational-related accidents. A lighting-related injury study was
prompted by the high number of serious accidents involving electricians (Wolfman and Capelli-Schellpfeffer, 2002).

Prior safety research involving mine lighting aimed to improve

safety by increasing the light output. It was noted that accident

rates decreased as much as 60% when the overall illumination

was increased (Sanders and Peay, 1988). Other researchers noted

dramatic increases in the ability of miners to see loose rock as illuminance increased from 500 to 1500 lux (Trotter and Kopeschny,

1997). Recent NIOSH research has focused on the spectral characteristics of light from miner cap lamps to improve safety. The results indicate significant gains in visual performance that could

reduce pinning/striking accidents (Sammarco et al., 2009a), glareinduced accidents (Sammarco et al., 2009b), and slip/trip/fall

(STF) accidents (Sammarco and Lutz, 2007). These accidents pose

major risk to miners. For instance, our analysis of Mine Safety

and Health Administration (MSHA) accident data for 2003–2007

indicates that for underground mining, STFs are the third leading

accident class (17.8%, n = 2441) of lost-time injuries. For 2007, STFs

resulted in 42,716 non-fatal days lost of work for all US coal mining

operations (US Mine Safety and Health Administration, 2007).

High brightness, white light emitting diodes (LEDs) are emerging as a viable replacement for traditional (i.e. incandescent and

florescent) lighting in mines. LED technology has the potential to

improve mine safety in several areas. Illumination from LEDs can

potentially improve a miner’s visual performance for the detection

of mine hazards. LEDs can be used for visually communicating

warnings and alerts. LED technology can provide longer service life

and require less power than traditional mine lighting technologies. LEDs could provide, depending on the design and ambient

conditions, useful lives up to 50 times longer than incandescent

lighting technologies commonly used in mining thus greatly

reducing exposure to maintenance-related hazards associated with

lighting. Reduced power requirements can enable reductions in the

size and weight of mine lighting. LEDs can also enable the elimination of power cords that tether miner cap lamps to wearable

battery packs. These power cords are known to contribute to

accidents when they get caught against equipment or protruding

hazards.

Mine lighting safety research has not been conducted to address

operational and maintenance-related accidents. MSHA data from

2002 to 2006 indicated that there were a total of 74,154 mining

accidents in all of mining, with about 24.5% occurring during maintenance-related activities (US Mine Safety and Health Administration, 2002–2006). This significant number of accidents during

maintenance further motivates more detailed analysis. Therefore,

the objective of this study is to better understand the nature and

extent of these accidents, and determine if LED technology has

the potential to reduce operational and maintenance-related accidents of mine lighting systems.

2. Solid-state LED technology

Mine lighting systems, as with other lighting systems, typically

consist of a light source (lamp), a lighting fixture, optics, a power

source, and drive electronics (ballast). Incandescent and halogen

light sources do not require drive electronics because they can

operate directly from the power source; however, fluorescent

and metal-halide light sources require drive electronics known as

ballasts. LEDs usually require drive electronics to regulate current

to the LED. The light output efficiency depends on the entire lighting system so caution must be used in looking at the light source

efficiency. There are many variations in mine lighting systems,

but this paper focuses on the light source and the associated drive

electronics, if any, to enable a direct comparison of light source

technologies.

The photometric and energy characteristics of LED light sources

differ in important ways (Bullough, 2003) (Sammarco et al., 2008).

In general, LEDs exhibit longer life and thus require less maintenance with respect to light source replacement. A light source’s

usable life is important because it will dictate light source replacement requirements, which is a maintenance activity. LED lighting

systems could, depending on the design and ambient conditions,

have a useful life that exceeds 50,000 h. By comparison, an incandescent cap lamp bulb could last 800–1200 h, and metal-halide

light sources could last 7500–20,000 h. LEDs also differ from current mine lighting technology in other ways. LEDs consist of a

semiconductor die encapsulated by a clear, solid resin, so they

are much more durable than other lighting options. Most importantly, there are no glass envelopes to break such as with incandescent, halogen, fluorescent, and metal-halide lighting sources. In

addition, there are no incandescent filaments to break that could

result in a catastrophic failure and subsequent replacement of

the light source.

LEDs do not typically fail catastrophically such as with incandescent light sources; rather, they gradually decrease in light output over time. LED life is defined by lumen maintenance that is

typically reported as the operating time (L) in hours that corresponds to a set reduction in the initial light output. For general

lighting, the useful life (lumen maintenance) is denoted by L70,

which corresponds to a 30% reduction of the initial light output;

this is the approximate threshold considered acceptable by most

of the occupants within a space (Alliance for Solid-State Illumination Systems and Technologies, 2005). Note that L70 denotes a general threshold for detecting light reduction and is not related to

human visual performance required for safety. Fig. 1 depicts lumen

maintenance values for various light sources that are commonly

used in mining.

LEDs also use less electrical power than conventional incandescent or halogen lighting sources. Energy consumption is especially

important for portable lighting applications. As the energy efficiency increases, the portable lighting system power source (battery or generator) can become smaller and lighter. Energy

efficiency, the ratio of light output in lumens (lm) to input power

in watts (W), is expressed as lm/W. This energy efficiency is typically known in the lighting industry as luminous efficacy because

this measure has dimensional units. Efficiency is used to describe

dimensionless measures such as the energy efficiency of drive electronics, which is quantified by the ratio of input power to output

power. Table 1 lists the typical ranges of luminous efficacies for

various light sources, as of October 2007. The Department of Energy’s luminous efficacies goal for white LEDs is 160 lm/W in

cost-effective, market-ready systems by 2025 (US Department of

Energy, 2009a). A luminous efficacy of 139 lm/W for commercially-available, cool-white LEDs was made available during

2009. During early 2010, 208 lm/W was reported achieved for a

white LED in a research laboratory (Cree, 2010). LED luminaires

could use up to 90% less energy as compared to incandescent light

sources commonly used in mining. The reduced energy consumption can enable new designs of miner cap lamps. For instance, the

typical incandescent cap lamp requires about 4 W of battery

power. The most recent designs of LED cap lamps require less than

one watt of battery power, enabling integration of the battery and

cap lamp headpiece. This will eliminate the electric cable that connects the headpiece to the battery pack worn on the miner’s belt.

The electric cable presents a hazard given that it can be caught

on an object.

Overall, it appears that luminaires using LEDs have the potential

to significantly reduce the frequency of accidents related to the

maintenance and repair of lighting systems. The long life of LEDs

would enable an exposure reduction to the associated hazards.

Consequently, risks would be reduced. Secondly, LEDs use signifi­
cantly less power compared to other lighting technologies. New

designs can be realized that could reduce battery power enabling

new cap lamp designs that eliminate hazards associated with the

electric cable. Lastly, LEDs could reduce the frequency of accidents

related to the loss of light during operation, given they can provide

useful light in excess of 50,000 h of operation as compared to about

1000–3000 h for an incandescent bulb. lumen maintenance (%)

100% 

90% 400Watt Metal Halide 

28Watt T5 Flourescen t

80% 

32Watt T8 Flourescen t 

70% Hi-power white LED 

100 Watt

60% Incandescent. 

50% 

0 5000 10000 15000 20000 

operating time (hr) 

Fig. 1. Typical lumen maintenance values for common light sources. Adapted and used with permission (Bullough, 2003).

Note that there is a wide range of ‘‘white” available for LEDs;

note the ‘‘warm” and ‘‘cool” LED types in Table 1.

Table 1

Luminous efficacies for various light sources as of October 2007. Adapted from the US

Department of Energy (2009a).

Light source Typical luminous

efficacy range (lm/W)

Incandescent (no ballast) 10–18

Halogen (no ballast) 15–20

Compact fluorescent (CFL) (includes ballast) 35–60

Linear fluorescent (includes ballast) 50–100

Metal halide (includes ballast) 50–90

Cool white LED 5000 K (w/LED drive circuit) 47–64

Warm-white LED 3300 K (w/LED drive circuit) 25–44

The range is

dependant on the light source type and wattage rating. A coolwhite type of LED is characterized by a correlated color temperature (CCT) between 5000 K and 10,000 K. Warm-white LEDs typically have a CCT from 2600 K to 3700 K. The CCT for warm-white

LEDs is similar to that for incandescent lamps. Warm-white LEDs

generally have a lower efficacy compared to cool-white LEDs.

3. Methods

The Mine Safety and Health Administration (MSHA) is empowered by statute to collect detailed information on accidents, injuries, and illnesses that occur in the mining industry. MSHA also

collects information about mines, employment, and production.

MSHA mining accident and illness annual records (US Mine Safety

and Health Administration, 2002–2006), maintained as SPSS data

documents by the National Institute for Occupational Health and

Safety (NIOSH), were used as the basis for this study. A narration

section contains a brief description of the accident. Narrative fields

for the years 2002–2006 were searched for key words including:

‘fixture(s)’, ‘bulb(s)’, ‘lamp(s)’, ‘light(s)’, ‘lighting’, ‘luminaire(s)’,

‘caplamp(s)’, and ‘caplight(s)’. These records, containing 60 fields

of information, were then imported into Excel for further analysis.

Non-germane incidents, such as when an employee hit his/her

head on a cab dome light while going over a bump, were discarded.

Mine accident reporting requirements are defined by Section 50.20 of Part 50, Title 30 Code of Federal Regulations. The regulations (Section 50-20-6) also define potential causes or

contributing factors as categorized by 12 accident/injury codes

that pertain to mining equipment, protective items, compliance issues with rules and regulations, and operator issues such as job

skills, training, and attitude. These codes are listed on a single page

form, MSHA Form 7000-1 Mine Accident, Injury, and Illness Report,

that is used to report accidents by mine operators and independent

contractors working on mine properties. Section C of the form has

an area for a narrative to describe contributing conditions and actual cause(s).

The MSHA accident/injury database is one of the most extensive

industrial safety databases. It encompasses all types of mining

including underground and surface metal, nonmetal, stone, and

coal mines. It also covers metal, nonmetal, stone, and coal mills

and plants, along with sand and gravel operations. Contractors

are also included. The authors note, however, that there are limitations. Mine lighting is not listed as one of the injury classification

options on the accident form. Poor illumination is seldom cited

as a cause or contributing factor in MSHA accident data. Incidents

may be documented by persons with expertise is mining, but not

necessarily in accident analysis nor in mine illumination; therefore, it is unlikely that root causes and contributing factors involving the human factors of visual performance or illumination can be

discerned. Another limitation is that not all accidents may actually

be reported, especially those resulting in very minor injury. Conversely, some events may be reported that result in no injury.

The narration texts also may contain misspellings or atypical

descriptions of circumstances that may hamper word searches. Finally, the accident narration may be overly brief or somewhat

cryptic, which may lead one to misread the rationale for the worker’s actions. For instance, the narrative description might simply

state that the miner was installing a light fixture when the accident

occurred. In this case it is not known whether the installation was

being done to enhance a poorly lighted area or to replace a faulty

fixture.

4. Accident analysis results and discussion

A total of 140 relevant accident records were found, averaging

28 annually. The leading mine commodity categories were 64 accidents (46%) in bituminous coal mines and 35 accidents (25%) for

stone mining as depicted by Fig. 2. Given all commodities, 105

accidents (75%) occurred during surface mining operations with

38 accidents (27%) at mills or preparation plants. Thirty-five accidents (25%) occurred during underground mining operations. For
surface mining accidents, the leading injuries were cuts (31),

sprains/strains (27), and fractures (10). For underground mining

accidents, fractures (12) and sprains (8) predominated.

sand & gravel, 

8 

nonmetal, 12 

metal, 21 bituminous 

coal, 64 

stone, 35 

Fig. 2. Lighting accidents by mining classification.

All of the accidents were non-fatal, but resulted in a total of

3668 days lost with an additional 925 days of restricted activity.

The leading injuries were sprains/strains (40), laceration/puncture

wounds (39), fractures/chips (18), or contusions/bruises (13). The

most common body parts injured were the fingers (26) followed

by the back (18), multiple parts (14), and the eyes (10). There

was a notable absence of injuries from lighting burn hazards which

could be explained by the required guarding around lights to prevent burn accidents. The leading accident classifications were handling materials (34%), followed by slip or fall of person (28%),

powered haulage (11%), hand tools (8%), and machinery (7%). The

MSHA accident classifications relate to the circumstances that contributed to the accident. Most accidents could be separated into

three main groups associated with maintenance, repair, and operation of cap lamps, auxiliary lighting, machine-mounted lighting,

and portable or fixed lighting.

The distribution of worker ages in Fig. 3 shows a high percentage occurring in the 45–55 age group with a median of 44 years

old.

55+ 

80 

70 

Number of incidents 60 

50 

40 

30 

20 

10 

0 

16-24 25-39 40-54 

Age Groups 

Fig. 3. Age distribution of workers in lighting accidents.

Total mining experience averaged 10.5 years with an average

of 7.7 years at the particular mine and job. Fig. 4 shows that, except

for the oldest group of workers, experience with a particular job increased with age as expected.

10 

Average Experience, Years 9 

8 

7 

6 

5 

4 

3 

2 

1 

16-24 25-39 40-54 55+ 

0 

Age Groups 

Fig. 4. Average worker experience with a job versus age.

The leading job titles of the employees were electricians (31), mechanic/repairman (31), and laborer

(20). These job titles account for 59% of the 140 accidents.

4.1. Maintenance, repair, and operation of machine-mounted lighting,

and portable or fixed lights

Lighting is used in mines to illuminate workplaces and areas

where employees routinely travel. It may consist of machinemounted lights, portable, or fixed lights. Illumination of work areas

is needed both underground and on the surface. The greatest percentage of accidents (53%) occurred when employees were maintaining or repairing light bulbs or light fixtures. Maintenance of

lights may involve cleaning or replacement of bulbs. Light fixtures

may need to be replaced if subjected to damage. Often, hand tools

are also needed to perform their work. Maintenance activities require workers to walk to the area of the mine where the light

maintenance is needed, and might involve climbing ladders and

placing their bodies in awkward positions. Thus, worker exposure

is increased to slip, trip, or fall hazards, moving machinery hazards,

and hand-tool related hazards. Lastly, workers are exposed to broken glass hazards if the light has been damaged. Lacerations have

occurred even though workers were wearing gloves. The longer life

and packaging (no glass envelope) of LEDs would decrease the

exposure to these hazards. Thus, the risk, a product of accident frequency and severity, would be decreased.

Seventy-four accidents (53%) occurred during lighting maintenance, predominantly while changing light bulbs. The accident

severities were significant. Although 37% of the maintenance, and

repair accidents resulted in non-fatal days lost injuries, the days

away from work averaged 78.4 per incident. The remainder yielded

no days lost. Eleven workers were hurt while using a ladder. Many

of these occurred when personnel over extended their reach. In five

cases, the ladder collapsed and wrist, back, hip, and leg injuries

were sustained. Five workers fell from a ladder, while two were

hurt positioning it. One worker slipped on a wet surface while dismounting. While standing on vehicles, two workers slipped while

changing lights. For the maintenance worker, fixtures must be held

in place with one hand while the other hand pulls wire or operates

a tool. Four employees sustained lacerations to hands/fingers on

the sharp fixture edges while another was cut while splicing wires.

There were five instances where employees received cuts when the

bulb being removed broke in their hands. Eye injuries resulted

when a bulb of the wrong voltage exploded following installation

and when dust was put in suspension. Three employees lacerated

their hands while popping open light covers with knives, and one

injured an eye with a popped cover. One worker was shocked while

changing a light bulb.

There were 27 injuries associated with the repair of lights and

fixtures. These occurred in a variety of fashions. Among the total,

three happened when employees slipped while dismounting vehicles after repairing lights. One employee was struck by a service

truck after pulling up to a dozer to repair lights. Three were cut

on broken bulbs. Three workers were cut using knives to strip wire.

While removing or repositioning fixtures, three were injured when
the fixture fell, while another was shocked during fixture removal.

Safe work practices concerning ladder safety and eye and hand

protection would likely have eliminated or reduced the accident

severity. Some workers were wearing gloves but still received hand

lacerations. The role LED technology plays in these accidents is in

reducing the need for maintenance thus reducing exposure to

these maintenance-related hazards.

There were accidents related to the operation of lighting. Thirty

accidents occurred while personnel were working or walking in

the vicinity of operating lights. Three workers suffered burns to

the eyes and skin from a 1000-W mercury vapor flood light operated with a broken outer shell at a gold processing plant. In another incident two employees at a surface coal mine were eating

lunch near a metal halide lamp with a broken outer shell and received ultraviolet burns to the eyes. At a copper mine, an unguarded light exploded cutting the eyes of two nearby workers.

One worker was cleaning a housing with a solvent and was burned

on the face and neck when a halogen work light ignited vapors. Finally a worker suffered burns to the face and neck when he

brushed against an unguarded light. The cooler operation temperatures and lack of UV radiation of LED lights would have precluded

these injuries. A number of incidents could be tied to catastrophic

failures of lighting. One worker tripped over the tongue of a welder

in an area where a light had gone out. Two accidents occurred

while employees were operating mobile machinery with headlights out. One involved a haulage vehicle that struck the rib at

an underground potash mine; the operator suffered neck and back

sprains and missed 97 days of work. The other incident involved

two vehicles, one without lights, at an underground coal mine.

Overall, it appears that LEDs have the potential to significantly

reduce the frequency of accidents related to the maintenance,

operation, and repair of lighting systems because the long life of

LEDs would enable an exposure reduction to the associated hazards; thus, risks would be reduced. To help facilitate risk assessment, accident severity and frequency categories have been

recommended for mining in Table 2 (Komljenovic et al., 2008

Sammarco, 2005) and 3 (Sammarco, 2005), respectively.

Table 2

Frequency category examples. Adapted from (Komljenovic et al., 2008).

Category Specific individual item Example frequencies

(work h/year)

Frequent Likely to occur frequently >1.0E-04

Probable Occurs several times in the 2.5E-06 to 1.0E-04

life of an item.

Occasional Likely to occur some time 1.0E-07 to 2.5E-06

in the life of an item

Remote Unlikely but possible to 1.0E-08 to 1.0E-07

occur in the life of an item

Rare So unlikely, it can be assumed <1.0E-08

occurrence may not be experienced

The frequency categories of Table 2 are based on the total number of

hours worked annually for all employees, including contractors

but excluding office workers, and for all commodities. Using MSHA

data from 2002 to 2006, the average annual work hours are about

609.5 million work hours (US Mine Safety and Health Administration, 2002–2006). A subjective risk assessment can be made by

using a risk matrix tool as depicted by Table 4. The potential risk

reduction enabled by LEDs could be significant. As an example,

24 accidents (62%) resulted in lost work days that correspond to

a severity category of marginal (Table 3).

Table 3

Severity category examples recommended for mining (Sammarco, 2005).

Category Example definitions

Catastrophic Death or multiple deaths

Critical Severe injury, permanent disability (partial or total)

Marginal Moderate injury, medical treatment and lost work days

Negligible Minor injury, first aid treatment and no lost work days

The average frequency

of these 24 accidents per work hours per year is less than

0.39E-07 so the frequency category is remote (Table 2). The resulting risk index (Table 4) is ‘‘C,” which suggests it could be an acceptable risk with management review and approval.

Table 4

Risk assessment matrix.

Catastrophic Critical Marginal Negligible

Frequent A A A B

Probable A A B C

Occasional A B B C

Remote B C C D

Rare B C C D

Risk index suggested criteria.
 

A – unacceptable risk.
 

B – undesirable risk.
 

C – acceptable risk with management review and approval.
 

D – acceptable risk without review or approval.
 

However, using

the total worked hours for all of mining to determine frequency

can yield a misleading result because all the people are not exposed to maintenance-related hazards. According to labor statistics

for 2007, about 53,850 people directly employed in mining are in

electrician occupations and installation, maintenance, and repair

occupations (US Bureau of Labor and Statistics, 2008b). This represents about 24% of all people directly employed in mining. This 24%

is conservative given that not all those in installation, maintenance, and repair occupations would be installing or maintaining

lighting. Electricians are the most likely workers to be involved

in maintaining lighting and they comprise only about 3% of all people directly employed in mining. Taking a conservative approach

by using 24%, the frequency is about 1.64E-07 so the category is

occasional (Table 2). The resulting risk index (Table 4) is ‘‘B,” which

suggests it could be an undesirable risk. Continuing the example of

the potential risk reduction potential of LED-based lighting for

maintenance-related accidents, consider the maintenance required

for incandescent lighting that could last 750–1000 h before failing

catastrophically and resulting in no light output. This typical life

can be shortened if the incandescent bulb is exposed to shock,

vibration, or voltage fluctuations all of which are common in mining. It could take 50,000 h for an LED’s light output to decrease 30%

and require replacement. Note that this is not a catastrophic failure

that results in no light output. Therefore, an incandescent light

source would be expected to need approximately 28 lamp replacements before an LED would need replaced. Translating this factor

of 28 to the frequency categories of Table 2 reduces the frequency

from occasional to rare with the resulting risk index reduced to C.

4.2. Personal cap lamp cables

Personal illumination in mines is provided by a cap lamp that is

typically the primary and most important source of light (Trotter

and Kopeschny, 1997). Traditionally, miner cap lamps used an

incandescent bulb as the light source and a lead-acid battery. Today, LED light sources and lithium technology batteries are gaining

acceptance.

The main parts of a typical cap lamp are the headpiece, battery,

and an interconnecting cable. The cap lamp headpiece contains the

light source and is mounted on the top of the employee’s protective helmet or hard hat. The cap lamp is powered by a battery

mounted in a pouch that is worn on the miner’s belt. Typically,

lead-acid batteries weighing about 2.2 kg (4.8 lbs) have been used.
Newer battery technologies such as lithium ion and nickel-metal

hydride are gaining wide usage due to the significant reductions

in size and weight. The lithium ion batteries are about one-third

the weight of a lead-acid battery. The battery, regardless of the various battery technologies, connects to the cap lamp headpiece by a

flexible electrical cable that contains two 18-gauge insulated wires.

The cable is firmly attached to the battery and to the cap lamp

headpiece. Disconnection requires the removal of mechanical fasteners. The cord diameter range is 0.838–0.884 cm (0.330–

0.348 in.) and 1.6 m (63 in.) in length. Some manufacturers provide

a longer, 1.7 m (66.9 in.) cable for taller miners. The cable can hang

over the front of a miner’s torso or over the miner’s back or side.

Placement of the cable and the battery is a matter of personal

preference.

The cap lamp cable can be loosely hanging, thus it can pose a

hazard of getting caught on or hitting against an object or a

machinery control lever. Consequently, the miner’s head could be

jerked back and the helmet could be pulled off; the cable could

interfere with a control lever and cause the machine to unexpectedly move; the cable could become entangled and the miner could

be pulled into moving parts or be dragged by moving machinery

(Blake et al., 1980). The hazard potential varies due to cable and

battery placement, the miner’s physical size and weight, the physical positioning of a miner’s body, and the miner’s proximity to the

mining machine. The height of miners varies considerably when

considering the seated height to eyes. The range is 68.5 cm

(27 in.) for the 5th percentile female to 84.8 cm (33.4 in.) for the

95th percentile male. There is a 91.44 cm (36 in.) difference in

cable length versus height for a 5th percentile female. This excess

cable poses a hazard that has a greater likelihood of causing an

accident. The analyses of MSHA data reveal that the cord is also a

hazard that could result in injury. Coiled cap lamp cables were recommended as a safety intervention that could reduce the risk to

miners (Blake et al., 1980). However, this intervention was never

implemented in the industry.

During the period 2002–2006, there were 24 incidents in the

mining industry involving the miner’s cap lamp cable getting

caught on an object. Nine resulted in no days lost while the

remainder, though non-fatal, averaged 44 days away from work

per incident. As expected, 83% (20) occurred underground, with

bituminous coal the leading commodity (29 occurrences). Cables

were caught in/on diverse items, including the tram levers of roof

bolters and a continuous miner, a drill steel rotation lever, a bridge

carrier, and a mucker door handle, and a belt splice. The cables

caught on machine controls caused unintended machine movements, running over the victims’ feet. One worker was struck in

the face by a drill steel. Others fell after their cable snagged a roof

bolt, a canopy post, a drill steel following a small roof fall, a steering wheel for a material handler, an overcast handrail, or a conveyor belt. A worker tripped over a cable while carrying the cap

light and another was sitting on a portion of the cable. Insufficient

lighting from a cap lamp was either the direct or indirect cause in

two accidents. An employee tripped when his light was going dim.

Another twisted a knee by stepping in a hole that was not seen because his cap lamp failed.

Currently, LED technology is being used for cap lamps in the US

mining industry. All of these cap lamps use a cable to a battery. The

current design of these cap lamps cannot enable the elimination of

the cable because the luminous efficacy is too low. In the future, it

would be expected that LED cap lamps in the US would be cordless

because of the rapid progress in LED efficacy. Cool-white LEDs in

2005 had luminous efficacies of about 20 lm/W. Assuming 80%

electronic driver efficiency, the resulting luminous efficacy is

16 lm/W. Today, LED luminous efficacies have significantly increased. Cool-white LEDs are available at 100 lm/W. Assuming

80% electronic driver efficiency, the resulting luminous efficacy is

80 lm/W, which would require about 20% of the electrical power

compared to the 2005 example. Thus, the technology for cordless

LED cap lamps appears to be viable today.

4.3. Auxiliary lighting

Mobile light plants are used in surface areas of mines to provide

concentrated illumination where work is taking place, such as

highwalls. They consist of a bank of lights mounted on a tower that

can be raised or lowered via a hand winch. These plants can weigh

2000 lb, so they are towed to a needed location by hitching to a

vehicle. Power for the lights is typically provided by an onboard

generator. These mobile plants typically contain four 1000 W metal-halide light sources, each producing about 110,000 lm.

From 2002 to 2006, there were 12 accidents involving light

plants in the mining industry. Eleven of these involved lifting or

moving the light plant. All occurred at surface mines with bituminous coal (4), limestone (3), and copper ore (2) as the leading commodities. Six resulted in days lost, averaging 25.3 days per

incident. Typically, accidents occurred when employees attempted

to hitch the light plant to the truck. The light plant would inadvertently move and a hand or foot injury would result. Others strained

their backs or shoulders attempting to lift the light plant. Two injured their hands with the winch handle or crank as they were

lowering the light plant tower.

Metal halide lamps produce light in the range of 50–90 lm/W,

making them more energy efficient than fluorescent lamps and

incandescent lamps (Table 1). Metal halide lamps have an efficacy

comparable to commercially-available LEDs. The current state of

LED technology would not enable a power reduction for mobile

light plants because LED efficacy, measured by lm/W, is approximately equal to the metal halide lamps currently used for portable

mine lighting. Thus, the light plant size and weight would remain

about the same. However, in the near future this should change given the rate of LED technology advancements. By 2015, if LED efficacy projections are met, cool-white LEDs efficacy will be 188 lm/

W (US Department of Energy, 2009b). Assuming a 90% efficiency

for the drive electronics and neglecting the fixture, the result is

169 lm/W. This is a 58% energy reduction assuming an average

70 lm/W efficacy for metal halide.

5. Summary and conclusions

From 2002 to 2006, an average of 28 accidents involving lighting occurred annually within the US mining industry. Nearly half

occurred in bituminous coal mines. Most the incidents could be

separated into three main groups associated with operation and

maintenance/repair activities, cap lamps, and auxiliary lighting.

The greatest number of accidents occurred when employees were

maintaining or repairing lighting. This is also the area of greatest

severity as measured by the days away from work.

These 28 accidents a year represent an undesirable level of risk

when looking at the exposure to those workers involved in maintaining or repairing lighting in mines. The longer life and robustness of LED lighting systems can potentially reduce the

frequency of accidents associated with maintenance, repair, and

the catastrophic lamp failures occurring during operation. To a lesser extent, it appears that LEDs could reduce accident severity for

the cases of eye injury from an exploding bulb and the eight cases

of cuts from broken glass. For these cases, the hazards would be

eliminated by the LEDs given the physical construction of this light

source.

Elimination of the cap lamp cable could eradicate cable-related

accidents. It is anticipated that new LED cap lamp designs will use

high efficacy (100 lm/W) cool-white LEDs thus enabling consider­
able power reductions such that the battery that it will be integrated with the cap lamp headpiece, thus eliminating the cable.

Major changes such as reductions in power, size, and weight in

mobile light plants do not seam achievable given today’s state of

LED technology; however, by 2015, LED efficacies could enable

such reductions of about 50%. While these reductions could potentially reduce the risks associated with lifting or moving mobile

light plants, this is not a major safety benefit for LEDs given that

only six accidents involving days lost from work occurred from

2002 to 2006.

Thus it appears that overall, LED technology could provide some

added safety benefits in terms of reducing operational and maintenance-related accidents involving lighting. This is primarily through

reduced hazard exposure given that LEDs could potentially reduce

lamp replacement by a factor of 28 as compared to incandescent

bulbs. However, given the risks posed by other accidents the primary

benefit of LEDs is likely to be improving the visual performance of

miners such that they can better detect mining hazards.

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