GHomce@cdc.gov

 

 

 

 

 

 

 

 

 

 

 

Protecting Miners from Electrical Arcing Injury 

James C. Cawley, P.E., and Gerald T. Homce, P.E. 

 Abstract - Electrical arcing injuries are the most common 

form of electrical injury in mining. MSHA data show that 381 

“non-contact electric arc burn” injuries occurred in the mining 

industry from 1996 - 2005. A more detailed study of data from 

1990-2001 showed that five types of apparatus - circuit breakers, 

conductors, nonpowered hand tools, electrical meters and test 

leads, and connectors and plugs were involved in two-thirds of 

the lost workday injuries. Many of the protections from 

electrical arcing injury available to workers in other industries 

stem from the application of National Fire Protection 

Association Standard 70E - Standard for Electrical Safety in the 

Workplace (NFPA 70E). NFPA 70E is a generally accepted 

industry guideline document, but excludes underground mining 

from its scope. Many of its practices and procedures, however, 

can be applied in the mining workplace to supplement the 

existing electrical safety requirements of Title 30 Code of 

Federal Regulations. This paper describes how NFPA 70E can 

be applied to mining workplaces after an analysis of the mine 

power system electrical arcing hazards has been completed (and 

Hazard/Risk Categories determined) using the tables from 

NFPA 70E or the calculation method as described in IEEE 1584. 

NFPA 70E can then be used to determine the levels and types of 

personal protective equipment (PPE) needed to protect miners 

against burn injuries. Appropriate lockout and tagout (LOTO) 

procedures for use in the mining industry are also described. 

Suggestions for better selection of electrically-rated hand tools 

are included. Recommendations for electrical meter selection 

and use based on transient withstand capability are also 

discussed.

 Index terms – arc, electrical arcing, PPE, burns, electrical 

shock, flame resistant, FR clothing, mining 

I. INTRODUCTION 1, 2 

Electrical injuries resulting from arc flash hazards are the 

most common form of electrical injury in mining. Fig. 1 

shows that “non-contact electric arc burns” (also referred to 

as arc burns or flash burns) (381 lost workday cases) were the 

leading source of electrical injury in nearly every major 

sector of the mining industry in a NIOSH examination of 

MSHA data covering 1996 - 2005. Injuries from electrical 

arcs are a serious problem in many other industries, too. 

IEEE Standard 1584 [3] gives detailed guidance for the 

engineering analysis of arc flash hazards using one-line 

1 NIOSH, Pittsburgh Research Laboratory, 626 Cochrans Mill Road, 

P.O. Box 18070, Pittsburgh, PA 15236. They can be reached by 

email at JCawley@cdc.gov & GHomce@cdc.gov 

2 The findings and conclusions in this report are those of the authors and do 

not necessarily represent the views of the National Institute for Occupational 

Safety and Health. 

diagrams and protective device settings for a specific 

installation. Standard NFPA 70E [5] addresses electrical 

hazards that are commonly encountered in the workplace, 

including arc flash hazards, and makes specific 

recommendations for protecting employees from these 

hazards. NFPA 70E gives detailed guidance for working on 

live equipment (although this practice is discouraged), 

lockout and tagout procedures, translating arc flash analysis 

data into “Hazard/Risk Categories”, and recommending 

specific clothing solutions to protect workers against serious 

burns. NFPA 70E also provides Hazard/Risk Category tables 

for specific electrical tasks that employees can reference 

during job planning when an engineering analysis of the arc 

flash hazard is unavailable. Underground mines are 

explicitly excluded from coverage by NFPA 70E. 

Underground mines, surface mines, and their associated mills 

and plants are subject only to Title 30 - Code of Federal 

Regulations (30 CFR) [6]. Parts 56, 57, 75, and 77 contain 

mining electrical safety provisions. 30 CFR does not 

explicitly require anything beyond rudimentary PPE for 

workers exposed to electrical arcing hazards. As the 

following statistics show, arcing injuries are a serious hazard 

in the mining industry, too. Miners could benefit from 

reduced injury incidence and severity by applying certain 

provisions of NFPA 70E. 

An earlier NIOSH study of 836 electrical accidents covering 

the period from 1990-2001 produced key findings about 

“non-contact electric arc burns”; these are summarized 

below: 

•	 55% of arc burn injuries occurred in bituminous 

coal, 21% in stone and 10% in sand and gravel 

•	 42% of arc burn injuries occurred underground, 26% 

in mills or preparation plants, and 22% in surface 

operations 

•	 Electricians (39%), mechanics (20%), preparation 

plant workers (6%), and laborers (5%) were the 

most often injured workers 

•	 In 52% of the cases involving injury to “mechanics/ 

repairman” the victim was performing “electrical 

maintenance/repair” 

•	 Electrical work activities were involved in more 

than two-thirds of the cases: 

− installation (2%) 

− maintenance (5%) 

− troubleshooting and repair (42%) 

− unspecified electrical work (22%) 

− failed in normal operation (19%) 

− Other (10%) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Comparison of Nonfatal Electrical Injury 

Types, 1996-2005 

0 

20 

40 

60 

80 

100 

120 

140 

160 

180 

200 

Anthracite 

Coal 

Bituminous 

Coal 

Metal Nonmetal Sand and 

Gravel 

Stone 

Mining Sector 

Number of Nonfatal Injuries

Electrical Shock 

Non-Contact 

Electric Arc Burn 

All Other 

Source: MSHA AII Database 

N = 793 

Figure 1. "Non-contact electric arc burns" outnumbered “electrical shock” injuries in every mining sector except Anthracite Coal and Nonmetal mining from 

1996 to 2005. 

•	 Two-thirds of lost work day accidents involved five 

electrical components: 

− circuit breakers (17%) 

− conductors (16%) 

− nonpowered hand tools (13%) 

− electrical meters and test leads (12%) 

− connectors and plugs (11%) 

•	 34% of the cases involved component failure: 

−	 19% involved an electrical component that failed 

in routine operation 

•	 Only 35% of cases (302 of 836 cases) reported 

voltage: 

− 84% (253 of 302 cases) occurred at less than 600 

V 

− 2% occurred at 601-1000 V
 

− 10% occurred at more than 1000 V
 

in particular. A measure of protection can be achieved by 

applying many of the concepts from NFPA 70E to the mining 

workplace. The information that follows assumes that the 

Hazard/Risk Category of the task has already been 

determined either from an engineering analysis of the mine 

power system or from an examination of Table 

130.7(C)(9)(a) from NFPA 70 E. 

II. WORK PRACTICES 

A. Lockout and Tag Out (LOTO) 

The preferred method of controlling electrical hazards is to 

establish what NFPA 70E calls an “electrically safe work 

condition” before commencing work.3

 This can be 

accomplished by properly locking out and tagging out the 

circuit. Many miners have been injured by contacting circuits 

that were not locked out or locked out improperly. NFPA 

The remainder of this paper will discuss how miners can
 

protect themselves from electrical injury and arc burn injury 3

 NFPA 70E, Article 120.
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2. A properly applied lock and tag. Note that the tag cannot be 

easily removed, contains the name of the person who applied it, and 

the date of the work. 

70E devotes considerable attention to proper LOTO 

procedures. A “complex” LOTO procedure involves systems 

or workplaces where multiple energy sources feed equipment, 

multiple crews, locations, or employers are working on the 

system at the same time, different or unusual disconnecting 

means are required in a specific sequence, or the job will 

continue for more than one shift. A complex LOTO requires 

one qualified person to be in charge of the LOTO procedure 

and only that person will install or remove locks and tags. 

The NFPA 70E LOTO procedure differs from the one 

described in 30 CFR Part 75.820. When a miner cannot 

remove their own lock (e.g., work extends beyond a single 

shift), MSHA allows another qualified person to remove a 

lock provided that the miner who installed it is told of the 

removal when they next report to work. 

Fortunately, most mining LOTO procedures are “simple” 

LOTOs. This means that only one person works on a circuit, 

that circuit has only one energy source, and that the job will 

be completed within one shift. The steps in a simple LOTO 

are straightforward: 

1.	 Wear appropriate PPE; 

2.	 Deenergize the equipment; 

3.	 Apply your lock to which you have the only key; 

keep the key in your pocket; apply your tag 

containing your name, the date, and warning others 

not to remove it; 

4.	 Visually verify (if possible) that switch blades are 

disconnected 4

; 

5.	 Ensure that no “backfeeding” occurs from another 

circuit; 

6.	 Release any stored energy; 

7.	 Verify that the equipment cannot be restarted; 

8.	 Test to ensure that the proper circuit is deenergized 

a.	 Using an appropriate meter on the correct 

setting, test the meter by measuring voltage 

on a known live circuit; 

b.	 Test the deenergized circuit for the 

presence of voltage between all conductors 

and between each conductor and ground; 

c.	 Retest for voltage on a known live circuit 

once again; 

9.	 Ground circuit conductors, if induced voltages could 

be a problem; 

10. Commence work; 

11. Remove installed grounding conductors before 

reenergizing; 

12. Wear appropriate PPE, then reenergize. 

Fig. 2 is an example of a properly applied lock and tag. 

B. Job Planning 

NFPA 70E recognizes that some work must be performed 

live. Exceptions are generally allowed when a shutdown 

“introduces additional or increased hazards or is infeasible 

due to equipment design or operational limitations.” 5

 For 

example, an exception is allowed when a shutdown would 

interrupt ventilation to a hazardous area. 

When work must be performed live, NFPA 70E suggests 

procedures beyond those described in 30 CFR6

 to protect 

miners against electric shock and arc flash injury. First, only 

qualified persons may perform live electrical work. Second, 

an “Energized Electrical Work Permit” should be obtained 

for the work.7

 The person requesting the live work must 

describe the job location, the work to be done, and justify in 

writing why the work cannot be deenergized or deferred until 

the next scheduled outage. In addition, the electrically 

qualified person doing the work is asked to: describe the job 

planning done for the task; explain what safety procedures 

will be employed; document the results of a shock hazard and 

arc flash hazard analysis; document the flash protection 

4

 MSHA requires the use of visible disconnecting devices on low and
 

medium voltage circuits (30 CFR 75.903) and on high voltage circuits (30 

CFR 75.808).

5

 NFPA 70E -2004, Article 130.1.
 6

 MSHA allows trouble shooting and testing tasks to be performed live when
 

necessary (30 CFR 75.509).

7 A sample Energized Electrical Work Permit is contained in Annex J of
 

NFPA 70E.
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

boundary; describe the required PPE; explain how access to 

the work site will be restricted; document that a job briefing 

was conducted, and; concur that the work can be done safely. 

Management is required to review, approve, and sign each 

request. 

A “Job Briefing and Planning Checklist” should be 

completed by those involved in the work. 8

 This checklist 

prompts workers and supervisors to consider a number of 

important aspects of the job planning process such as 

identifying the hazards (voltage, “back-feeding” voltage 

sources, unusual work conditions, and protection boundaries), 

and to reexamine whether the task can be performed without 

the equipment energized. It reminds the workers about 

lockout and tag out procedures, proper voltage measurement 

verification of lockout and tag out, and considerations for 

emergency preparedness. 

III. PERSONAL PROTECTIVE CLOTHING AND EQUIPMENT 

A. Establishing the Severity of the Electrical Arcing Hazard 

The preferred method of establishing the severity of arcing 

hazards is through an engineering analysis of the power 

system using IEEE Standard 1584. Such an analysis will 

produce specific information regarding the available fault 

currents on the system. Using these available fault currents 

and a detailed knowledge of protective device clearing times, 

arc flash energies can be estimated in cal/cm2

 for specific 

points in the mine electrical system. NFPA 70E classifies 

electrical arcing hazards into Hazard/Risk Categories 0 

through 4 using the level of incident arc energy predicted by 

the engineering analysis. 

B. Flame Resistant Clothing 

When a circuit cannot be deenergized to work on it, 

precautions must be taken against both electrical arcing and 

electrical shock injury. For arcing hazards, protections 

include flame resistant (FR) work clothing. Ordinary work 

clothing is usually made from 100% cotton, cotton-synthetic 

blends, or synthetic material alone. FR clothing is made from 

FR synthetic fabrics or FR cotton-synthetic blends. Some FR 

materials are inherently flame resistant while others are 

chemically treated. FR materials must meet the requirements 

of ASTM F-1506 [1], which defines their ability to self 

extinguish when controlled amounts of energy from an 

electrical arc is incident upon them. In addition, FR textile 

materials must resist the tendency of ordinary materials to 

“break open” during an electrical arc, exposing the wearer to 

further injury by having skin exposed directly to the electrical 

arc. 

8

 A sample Job Briefing and Planning Checklist is contained in Annex I of 

NFPA 70E. 

The ability of clothing or personal protective equipment 

(PPE) to withstand the energy from an electrical arc is called 

its Arc Thermal Performance Value 9 (ATPV) and is printed 

on FR clothing and PPE, usually on the label. Many users 

believe that FR garments sold as protection against arcing 

hazards will protect them from all injuries within the arc 

rating on the label. Such is not the case. The ATPV is the 

number of incident cal/cm2

 a FR garment can withstand while 

still offering its wearer a 50% chance of a sustaining no more 

than a second degree (curable) burn. Other PPE, such as face 

shields and full flash hoods are also characterized by their 

ATPV values and the meaning of the rating is the same. 

Non-FR materials that melt when exposed to electrical arcing 

or flame, such as acetate, rayon, nylon, polyester, 

polypropylene, spandex, etc., should never be worn, even as 

under garments, to perform electrical tasks. Wearing non-FR 

garments made from these materials exposes the wearer to 

injury from both the initial electrical arc and from the 

continued melting and burning of the fabric directly on the 

wearer’s skin. 

Table 1 shows that as the energy available from an electrical 

arc hazard increases, the Hazard/Risk Category increases 

from 0 to 4. The need for FR clothing with higher ATPVs 

increases, as well. In addition, the need for other FR PPE 

(face shields, flash suit hoods, switching coats, full flash 

suits, etc.) increases as well. The need for FR clothing with 

higher ATPVs can be satisfied in several ways. First, 

clothing of heavier single layered FR fabric weights (in 

oz/yd2

) can be worn. Alternatively, multiple layers of FR 

clothing can be worn to achieve a higher ATPV. For 

example, donning FR coveralls over FR work clothing 

increases the overall ATPV of the clothing system. Simple 

addition of the ATPV values of individual layers of FR 

clothing gives a conservative estimate of the ATPV value of a 

clothing system. An accurate estimate of the ATPV for 

layered FR clothing may be available from the clothing 

manufacturer. For higher-level hazards, switching coats and 

multilayer flash suits can be worn to yield successively 

increasing ATPVs when worn over the basic FR pants and 

FR shirt. 

C. Everyday Work Clothing for Mine Electrical Workers 

Everyday wearable FR work clothing is available from 

several manufacturers in the form of pants or jeans and long 

sleeve shirts. Workers at risk for electrical arc exposure 

should wear only underwear that is 100% cotton. Never wear 

underwear containing synthetic materials.10 Shirts must 

always be worn with the sleeves rolled down and neck 

9

 ATPV is defined in ASTM F 1959-99.
 10 An incidental amount of elastic in the waistbands of non-melting
 

underwear is allowed under NFPA 70E, Article 130.12 (c).
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TABLE 1 TABLE 2 

HAZARD/RISK CATEGORIES AND THEIR ASSOCIATED ATPV AND FREQUENCY OF BURN INJURY TO BODY PARTS EXPOSED TO 

CLOTHING REQUIREMENTS 11 ELECTRICAL ARCING. 

Hazard /Risk 

Category 

Required 

Minimum 

Arc Rating 

(ATPV) 

(cal/cm2

) 

Typical Protective Clothing 

Required 

0 2* 

Non-melting, flammable 

materials (i.e., untreated 

cotton wool, rayon, or silk, or 

blends of these materials) 

with a single fabric weight at 

least 4.5 oz/yd2

 (1 layer) 

1 4 FR shirt and FR pants or FR 

coverall (1 layer) 

2 8 

Cotton underwearconventional short-sleeved 

and brief/shorts plus FR shirt 

and FR pants (1 or 2 layers) 

3 25 

Cotton underwear plus FR 

shirt and FR pants plus FR 

coverall, or cotton underwear 

plus FR coverall (2 or 3 

layers) 

4 40 

Cotton underwear plus FR 

shirt and FR pants plus 

multilayer flash suit 

* See NFPA 70E-2004, Table 130.7 (C) (11) Protective Clothing 

Characteristics and Paragraph 130.7 (5) 

buttoned to provide the intended protection from electrical 

arcs. Shirts are available with ATPVs ranging from 4 to 8. 

The FR pants are available with ATPVs ranging from of 6 to 

11. FR work jeans are available with ATPVs up to 20. 

A typical work outfit consisting of a long sleeved shirt with 

an ATPV of 8 and work pants with an ATPV of 11 would 

provide everyday protections against electrical arcs up to 

Hazard/Risk Category 2. The addition of FR coveralls with 

an ATPV of 8 could be worn but the Hazard/Risk Category 

would remain at 2. Combined with appropriately rated face, 

eye, and hand protection this easily wearable outfit could 

protect a mine electrician against many common on-the-job 

electrical arcing hazards. 

D. FR Clothing for Higher Hazard/Risk Categories 

Hazard/Risk Category 3 (8-25 cal/cm2

) requires additional 

protective clothing to protect against burn injuries. Several 

clothing solutions are available. Two set of FR coveralls 

(each 11 cal/cm2

) worn over the everyday work outfit 

11 Face, eye, hand, and other PPE are also required for complete protection. 

They were omitted here to clarify the discussion of clothing requirements. 

For other PPE requirements based on Hazard/Risk Category, see NFPA 70E 

Table 130.7(C)(10). 

Body Part Frequency of Burn Injury 

Right hand 67% 

Right forearm 41% 

Left hand 56% 

Left forearm 34% 

Face, neck, head 50% 

(8 cal/cm2

 shirt and 16 cal/cm2 jeans) with an FR hood can 

increase the overall clothing system ATPV to cover arcing 

hazards in Hazard/Risk Category 3. Alternatively, a long 

sleeve undershirt (11cal/cm2

) plus the everyday work outfit 

plus one set of FR coveralls (11cal/cm2

) with an FR hood 

would also work. Hazard/Risk Category 4 requires the 

worker to wear cotton underwear, a FR shirt, FR pants, and a 

multilayer FR flash suit with FR hood. 

E. Face and Eye Protection 

When performing electrical maintenance and repair work, the 

hands, forearms, and face are usually positioned closest to the 

work. Consequently, these body parts often experience burn 

injury more often and, presumably more severely. One 

European guideline cites the frequency with which body parts 

sustained 1st, 2nd, or 3rd degree and higher injuries in 

electrical arcing accidents.[4] The results are shown in Table 

2. It is a good practice to always wear safety glasses with 

side shields on the job. However, safety glasses do not 

protect the wearer from electrical arcing hazards. There are 

no arc-rated safety glasses on the market as of this writing. 

To protect workers from serious injury to the face, eyes, and 

neck areas NFPA 70E requires that employees wear 

nonconductive head and face protection when the danger of 

head injury exists from exposure to electric shock or 

electrical arcing hazards.12 For Hazards/Risk Category 2, an 

arc-rated face shield with a minimum ATPV of 8 or more 

with wrap around guarding to protect not only the face, but 

also the forehead, ears, and neck, is required. (See Fig. 3) 

Alternatively, a flash suit hood with an ATPV of 8 or more 

could be worn. NFPA 70E also prohibits the use of face 

shields that are not arc-rated.13 Wearing a face shield that is 

not arc-rated may present a greater danger of serious injury 

than not wearing a face shield. Face shields that are not arcrated can melt and ignite during an electrical arcing event. 

The blast shockwave can then deform it back onto the 

wearer’s face. It may continue to melt and burn on the 

wearer’s face after the arc has been extinguished, causing 

injury even more severe than from the arc alone. 

12 NFPA 70E Article 130.7 (C)(3) 

13 NFPA 70E Article 130.7(C)(13)(b) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3. This worker is dressed for Hazard/Risk Category 2. He 

is wearing a hooded jacket and bib-overalls over FR work clothes, 

a combination face shield/hardhat over safety glasses, and 

voltage-rated gloves with leather protectors. 

In addition, always wear ANSI-rated safety glasses or 

goggles under a face shield. 

Three issues regarding face shields are problems for mine 

electricians. One is that the use of a face shield reduces 

transmitted light, making an underground workplace appear 

even darker. One possible solution is to use auxiliary lighting 

when working in electrical arc-prone situations underground. 

Newer face shield designs can now transmit about 70% of the 

available light to the wearer’s eyes. Another problem is that 

available face shields/hard hat combinations do not 

accommodate the standard miner’s cap lamp. Manufacturers 

of mine safety equipment should produce an arc-rated face 

shield/mine helmet combination to overcome this barrier. 

Finally, arc-rated face shields distort the wearer’s perception 

of color to some extent. Newer designs have less color 

distortion, but still present problems for tasks requiring good 

color vision. 

When an employee will be exposed to electrical arcing 

hazards determined to fall within Hazards/Risk Category 3, 

NFPA 70E requires employee head and face protection to be 

provided by a flash suit hood with an ATPV equal to or 

greater than the anticipated hazard.14 When Hazards/Risk 

Category 4 hazards are present, a full flash suit and an 

14 NFPA Table 130.7(C)(10) 

TABLE 3 

VOLTAGE-RATED GLOVE DESIGNATIONS 15
 

Class Maximum Working 

Voltage (Vac) 

00 500 

0 1,000 

1 7,500 

2 17,000 

3 26,500 

4 36,000 

appropriately rated flash hood, as described in Table 

130.7(C)(10), are required. 

F. Hand Protection 

Table 2 shows that the hands are the most often injured body 

parts in an electrical accident. They are usually the body 

parts closest to an electrical arcing fault when it occurs. For 

protection from electrical arcing hazards alone, the minimum 

hand protection recommended is a pair of heavy-duty leather 

(more than 12 oz/yd2

) work gloves for arcing hazards up to 

Hazard/Risk Category 2. For Hazard/Risk Category 3 or 4, 

arc-rated gloves made from FR materials should be used. 

When working where electrical shock hazards are present, 

voltage-rated gloves must be worn. As shown in Table 3, 

voltage-rated gloves are available from Class 00 (500 Vac) 

through Class 4 (36,000 Vac). A non-insulating inner liner 

can be worn next to the skin for moisture absorption and 

general comfort. Next, a rubber insulating glove covers the 

liner. Finally, a leather protector glove is worn over the 

rubber insulating glove to protect it from punctures, cuts, and 

abrasions in use. The rolled top of the rubber insulating 

gloves must extend up the forearm beyond the top of the 

leather protectors by at least 0.5-in for Class 00 or 0 gloves 

and by 1, 2, 3, and 4-in for Class 1, 2, 3, and 4 gloves, 

respectively. Never perform electrical work using the rubber 

gloves without the leather protectors. The rubber gloves 

alone are too susceptible to punctures and cuts. In addition, 

never wear the liners or the leather protectors alone without 

the rubber insulating gloves as protection from electrical 

shock. 

The rubber insulating gloves must be inspected before each 

use by inflating them and looking and listening for air leaks 

from pinholes, cracks, etc. Glove inflators are available for 

this purpose or the inflation can be done manually. Leather 

protector gloves must also be inspected for imbedded wire 

strands, metal particles, or other material that could 

15 Excerpted from ASTM F 496-02a Standard Specification for In Service 

Care of Insulating Gloves and Sleeves, Table 1, p2, available from ASTM 

International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, 

PA 19428-2959 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4. Hand tools electrically rated for 1000Vac can significantly 

reduce the likelihood of starting an electrical arc if accidentally 

dropped into equipment. 

compromise their ability to protect the rubber insulating 

glove underneath. 

IV. OTHER EQUIPMENT 

A. Electrically-rated Tools 

About one in eight electrical arcing accidents happened when 

non-powered hand tools such as screwdrivers, wrenches, 

pliers, etc., accidentally bridged two phase conductors or a 

single phase to ground while performing live work. Insulated 

hand tools are available that are ASTM rated [2] for 1000 

working volts AC and have a minimum of metal exposed 

with which to bridge nearby conductors. They are impact 

resistant and flame resistant. At least one brand of tools has 

two layers of insulation; a yellow inner layer and an orange 

outer layer. If the yellow insulating layer becomes visible, 

the tool’s insulation rating has been compromised and it 

should be discarded. Complete tool sets are available 

including open end and box wrenches, screwdrivers, pliers, 

cutters, and ratchet sets. (See Fig. 4) Never use ordinary 

uninsulated hand tools for live work. 

B. Meters and Test Leads 

About one in eight electrical arcing accidents happened while 

using a multimeter. One common type of accident involves 

taking measurements while using the wrong multimeter 

settings. For example, attempting to measure voltage with 

the test leads plugged into the current terminals can cause a 

low resistance fault across the source voltage. Newer 

multimeters beep to warn of this situation and are protected 

with a fuse that can clear a high-energy fault; older 

multimeters or inexpensive, non-professional multimeters 

may not be properly fuse protected and could seriously injure 

Figure 5. Test leads are marked with their CAT ratings. Make sure that the
 

CAT rating of your test leads matches that of the multimeter you are using.
 

the user. Never replace a blown multimeter fuse with 

anything other than an exact replacement fuse. The improper 

use of a 600-1000V multimeter to measure voltages higher 

than 1000Vac is a common theme in mine electrical 

accidents. The voltage rating printed on the multimeter is the 

maximum voltage it can measure. Attempting to measure 

voltages beyond the multimeter and test lead ratings often 

leads to an explosion, with accompanying shock and burn 

hazards. Always double check to ensure that your multimeter 

and test leads are voltage-rated for the circuit you want to 

 16, 17 measure.

Multimeters are often used in mining to measure electrical 

parameters on motors, switchgear and 480-600V three-phase 

ac circuits near their connection to utility power. Newer 

multimeters for use at or below 1000V are transient rated. 

This transient rating defines Overvoltage Installation 

Categories I through IV, often abbreviated as CAT I, CAT 

IV, etc. A mine power distribution system can be divided 

into categories based on the likelihood of the presence of 

high-energy switching or lightning transients. A multimeter 

with a higher CAT number is needed when working on a 

section of the mine electrical system close to the utility 

connection, where higher-energy transients are more likely to 

occur. A higher CAT rating (e.g., CAT III, CAT IV) denotes 

a multimeter designed to be more resistant to high-energy 

transients. Multimeters used in mining applications should 

be CAT-rated for CAT III or IV. Test leads are also an 

important consideration in multimeter safety. In addition to 

using multimeters with the proper CAT ratings, it is 

important to use test leads with at least the CAT rating of the 

multimeter. The CAT rating is listed on the test lead. (See 

fig. 5) Most professional multimeters are supplied with test 

16 The interested reader should go to the Fluke Corporation website
 

http://us.fluke.com/usen/apps/Safety/Default.htm for a more detailed 

discussion of multimeter Category ratings.

17 Mention of specific products, services, or manufacturers does not imply 

endorsement of those products, services, or manufacturers by NIOSH, CDC,
 

or the U.S. Government.
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

leads that match the CAT rating of the multimeter. In 

addition to their heavier insulation, these test leads have a 

minimum of exposed metal at the probe tips to prevent 

bridging conductors if the probe slips. In addition, a finger 

guard is used to prevent fingers from accidentally sliding 

onto the exposed metal of the probe tip. Never use 

uninsulated alligator clips to make measurements on live 

electrical connections. 

Whenever possible, use straps or hangers to attach the 

multimeter to a nearby grounded metal surface. This leaves 

both hands free to manipulate test probes and to make 

measurements. It also gets the multimeter out of the user’s 

hands in the event of a malfunction. 

V. SUMMARY 

Although IEEE 1584 and NFPA 70E provide guidance in 

other industries, they have yet to find wide application in the 

mining industry. Many of the protections from electrical 

arcing afforded other workers could easily be used by miners, 

too. It is important to thoroughly examine decisions to work 

live and rigorously prepare for such work via a more formal 

live work permitting system. A thorough knowledge of 

LOTO is also important. By applying a series of steps from 

NFPA 70E, LOTOs can be performed quickly and safely. 

Supplementing the existing electrical safety provisions of 30 

CFR with arc-rated FR clothing and face, eye, and hand 

protection could mitigate or prevent many of the electrical 

arcing injuries in the mining industry. After the Hazard/Risk 

Category is determined, either by calculation or by use of 

NFPA Table 130.7(C)(9)(a), appropriate clothing can be 

determined from Table 130.7(C)(11) and other PPE can be 

determined using Table 130.7(C)(10). Proper application of 

FR clothing and other arc-rated PPE is crucial to miner 

safety, especially for those who routinely work with 

electricity. In addition, the appropriate selection and use of 

tools and CAT-rated meters is also important to electrical 

safety. 

REFERENCES 

[1] ASTM F-1506-02a, Standard Performance Specification for 

Textile Materials for Wearing Apparel for Use by Electrical 

Workers Expose to Momentary Electric Arc and Related Thermal 

Hazards, available from ASTM International, 100 Barr Harbor 

Drive, P.O. Box C700, West Conshohocken, PA 19428-2959 

[2] ASTM F 1505-01 Standard Specification for Insulated and 

Insulating Hand Tools, available from ASTM International, 100 

Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 

19428-2959 

[3] IEEE Standard 1584 – 2004, IEEE Guide for Performing Arc 

Flash Hazard Calculations, available from IEEE, Inc., 3 Park 

Avenue, New York, NY 10016-5997 

[4] ISSA, 2000, Guideline for The Selection of Personal Protective 

Clothing When Exposed to the Thermal Effects of an Electric Arc 

[2000] ISBN-Nr. 3-9807576-3-3 available from the International 

Social Security Association, Electrical Section - Gas - LongDistance Heating – Water, c/o Berufsgenossenschaft der 

Feinmechanik und Elektrotechnik Gustav-Heinemann-Ufer, 50968 

Koln , Germany 

[5] NFPA Standard 70E-2004, Standard for Electrical Safety in the 

Workplace, available from NFPA, 1 Batterymarch Park, Quincy, 

MA 02169-7471 

[6] U.S. GPO, Title 30-Code of Federal Regulations – 2006 (30 

CFR) is available in print from the Government Printing Office at 

888-293-6498 or in electronic format at www.gpoaccess.gov/nara .