From Scotia to Brookwood, fatal US underground coal mine explosions

ignited in intake air courses

Thomas H. Dubaniewicz, Jr. *

National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236

abstract

The National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, conducted

a study of past mine explosions to identify the ignition locations and ignition sources responsible for the

most severe explosion events resulting in death. Since the Scotia disaster of 1976, many fatalities from

underground coal mine explosions have been linked to nonpermissible electrical equipment ignition

sources located in intake air courses. With few exceptions, explosion protected equipment is generally

not required in intake air courses of gassy underground coal mines in the US. Cigarette lighters were

another prevalent ignition source for fatal explosions ignited in intake air courses. Several mine rescue/

recovery teams have encountered electrical ignition hazards. The study provides evidence that intake air

courses of gassy underground coal mines fit the description of certain Hazardous (classified) locations

described in the US National Electrical Code. Class I Division 2 or Zone 2 explosion protection techniques may be used to design intake air equipment so that it does not present an ignition source under

normal operation, before mine power is shut down in emergency situations. Nonpermissible circuits in

intake air courses that are likely to remain energized during emergencies, e.g. battery powered equipment, should be protected by more stringent Class I Division 1, Zone 1, or Zone 0 techniques, to protect

rescue/recovery personnel.

1. Introduction

Several prominent US underground coal mine explosion disasters have been linked to electrical ignition sources located in intake

air courses. Thirteen miners were killed during the 2001 Jim Walter

Resources No. 5 mine, Brookwood, AL, double explosion disaster

(MSHA, 2002; UMWA, 2003). The Mine Safety and Health Administration (MSHA) investigation concluded that both Brookwood

explosions were probably ignited in intake air entries, and both

were probably ignited by electrical equipment. Twenty-six miners

were killed during the 1976 Scotia KY double explosion disaster

(Bethell, 1976; Richmond, Price, Sapko, & Kawenski, 1983; USMRA,

2007). The US Mine Rescue Association (USMRA) attributes the

ignition source for the first explosion (15 killed), to a normally

sparking battery powered locomotive in an intake air entry. The

large loss of life from the Scotia and Brookwood disasters suggested

that, even though releases of flammable gas into intake air courses

may be infrequent, ignition of these releases by nonpermissible

electrical equipment can lead to large numbers of fatalities.

Title 30 of the US Code of Federal Regulations (CFR) contains

federal coal mining safety regulations (30 CFR). The term permissible refers to equipment that meets MSHA specifications for the

construction and maintenance of such equipment, to assure that

such equipment will not cause a mine explosion or mine fire (30

CFR 75.2). Electrical equipment that is normally exposed to

methane or coal dust inby (closer to the working face than) the last

open crosscut (30 CFR 75.500), or within 150 feet of pillar workings

or longwall faces (30 CFR 75.1002), or in return entries (30 CFR

75.507), must be permissible. Any atmospheric monitoring system

operated during fan stoppages shall be intrinsically safe (30 CFR

75.313). Air quality detectors and measurement devices shall be

approved and maintained in permissible and proper operating

condition (30 CFR 75.320). Telephones and signaling devices shall

offer no probable explosion hazard under normal operation if used

in gassy or dusty mine atmospheres (30 CFR 23.6). Electrical

components of automatic fire sensors must be provided with

protection against ignition of methane or coal dust (30 CFR

75.1103-7). With these few exceptions, explosion protected electrical equipment is generally not required in intake air courses of

gassy underground coal mines in the US.

The National Institute for Occupational Safety and Health,

Pittsburgh Research Laboratory, conducted a study of past mine

explosions to identify the ignition locations and ignition sources

* Tel.: þ1 412 386 6596; fax: þ1 412 386 6764.

E-mail address: tcd5@cdc.gov
responsible for the most severe explosion events resulting in death.

(The findings and conclusions in this report are those of the author

and do not necessarily represent the views of the National Institute

for Occupational Safety and Health.) Fatalities linked to nonpermissible equipment ignition sources in intake air courses were

compiled and compared to other ignition sources and ignition

locations, to put the hazard posed by nonpermissible equipment in

intake air courses into perspective. Recommendations are provided

for preventing similar disasters in the future.

2. Historical summaries of coal mine explosions

US Bureau of Mines historical summaries of coal mine explosions provide many examples of explosions that were ignited by

electrical equipment such as trolley wires and motor control contactors (Dobroski, Stephan, & Conti, 1996; Humphrey, 1960; Richmond et al., 1983). These summaries used the term disaster to

describe events producing at least 5 fatalities. In the most recent

summary, Dobroski et al. (1996) provided overviews and causal

analyses of coal mine explosions from 1981 to 1994. Causal analyses

involved only violations of MSHA regulations, which did not

include normally sparking equipment in intake air entries. For

example, the McClure mine explosion in 1983 (7 killed), was ignited

by electrical arcing in possibly 6 pieces of equipment in intake air

courses, but the causal analysis involved only ventilation practices.

The causal analysis was similar to the Brookwood investigation in

this respect, which also made no mention of the electrical equipment design in the causal analysis (MSHA, 2002). Some explosions

in Dobroski et al.’s (1996) summary tables were categorized as

electrical, but a distinction was not made as far as the location of

the equipment, or if the equipment was faulted permissible

equipment or normally sparking electrical equipment. In the

current study, fatalities linked to nonpermissible equipment ignition sources in intake air courses were compiled and compared to

other ignition sources and ignition locations, to put the hazard

posed by nonpermissible equipment in intake air courses into

perspective.

Dobroski et al.’s (1996) summary tables did not account for

uncertainties associated with multiple possible ignition sources or

ignition locations. For example, the summary tables attributed the

Pyro William Station Mine disaster of 1989 to a cutting torch even

though the gas valves on the torch were found closed. The narrative

description of the explosion pointed out that other types of ignition

sources were considered possible in no particular order of likelihood. The possible ignition sources were at the face or in an intake

air course. In the current study, explosion fatality summaries were

weighted for cases where a most likely ignition source or location

was not identified, to better account for multiple potential ignition

sources and locations for comparison purposes.

3. Surveillance study methods

Fatal accidents categorized as ignition or explosion since 1976

were identified through the Mining Accident, Injury and Illness

(MAII) database (NIOSH, 2007). MSHA investigation reports for

fatal accidents since 1995 were downloaded from the MSHA web

site (MSHA, 2007). Fatal accident reports prior to 1995 were

obtained from the MSHA Technical Information Center and Library,

Beckley WV. Richmond et al.’s (1983) and USMRA (2007) accounts

of the Scotia disaster were used because an MSHA investigation

report was never released. The review did not include MSHA fatal

reports categorized as fire. The review did not include fatal reports

categorized as explosives that did not also involve ignition of gas or

dust. High wall mines, which are categorized as surface mines, were

included in the study because they involved explosions of methane

and coal dust ignited in openings mined under the surface.

Ignition locations were categorized as follows.

Unsealed Gob refers to the space left by the extraction of a coal

seam into which waste is packed or the immediate roof caves

and the area had not yet been sealed from the active workings.

Sealed area refers to a worked-out area (30 CFR 75.301) that is

sealed. Sealed areas were not required to be maintained as an

inert atmosphere prior to 2007.

Return air is defined as air that has ventilated the last working

place on any split of any working section or any worked-out

area, whether pillared or nonpillared (30 CFR 75.301).

Intake air is defined as air that has not yet ventilated the last

working place on any split of any working section, or any

worked-out area, whether pillared or nonpillared (30 CFR

75.301.) Intake air is taken to include belt air course, as 30 CFR

does not make a distinction between intake and belt air course

for electrical equipment permissibility purposes in methane

contaminated atmospheres.

Shaft refers to a vertical or near vertical excavation in rock for

the purpose of providing access to an ore body.

A high wall opening refers to an underground excavation into

the wall of an open-cut excavation.

A working face is defined as any place in a coal mine in which

work of extracting coal from its natural deposit in the earth is

performed during the mining cycle (30 CFR 75.2). Face refers to

areas inby the last open crosscut up to the working face or

within 150 feet of pillar workings or longwall faces.

Electrical equipment ignition sources were subdivided into two

categories.

Faulted permissible equipment refers to permissible equipment

that malfunctioned in a manner that defeated the explosion

protection feature of the equipment.

Nonpermissible equipment refers to electrical equipment not

identified as permissible and not required to be explosion

protected. Vehicle refers to locomotives or personnel carriers.

Vehicle ignition source categories were subdivided as battery

powered and trolley wire powered.

For cases where a single most likely ignition source or location

was not identified, the number of fatalities attributed to categories

of ignition sources or locations were weighted by the uncertainty

associated with each. For example, if an explosion resulted in 10

fatalities, and two possible ignition locations with five possible

ignition sources were identified in no particular order of likelihood,

each ignition location was attributed 5 fatalities, and each ignition

source was attributed 2 fatalities.

4. Results

Appendix Table A1 lists fatal methane and/or coal dust explosions in underground and high wall coal mines since 1976. All

intake air entry explosions occurred when the ventilation system

failed or was determined to be inadequate. All fatal intake air entry

explosions involved only methane initially. The severities of some

of these explosions were enhanced by coal dust suspensions after

the methane was ignited.

The 1989 Pyro No. 9 explosion disaster originated in one of two

different locations and could have been ignited by 5 different types

of ignition sources. An intake air entry was identified as the transition zone where a strong explosion developed, but a weaker

explosion originating on a longwall face that propagated to the

transition zone was also plausible. A cutting torch and igniter were

found at the face, although both gas valves on the torch were found

closed. A permissible scoop with multiple faults was found at the
face. An undetonated blasting cap was found near the transition

zone, suggesting blasting caps conceivably could have been

involved. A roof fall with pyritic inclusions occurring in the transition zone was a conceivable ignition source. A messenger wire

strung through the transition zone that could have snapped under

tension was a conceivable ignition source. The most likely ignition

location or source could not be determined.

The 1983 McClure and 1987 Double R explosions involved

multiple possible electrical ignition sources in no particular order of

likelihood. All six electrical ignition sources identified for the seven

McClure explosion fatalities involved equipment not identified as

permissible. Three of the four possible electrical ignition sources

identified for the Double R explosion fatality involved equipment

not identified as permissible.

One of the Brookwood miners may have received fatal injuries

from the first explosion prior to the second massive explosion. This

fatality was attributed to the first 2001 Brookwood explosion in

Table A1. The battery assembly cited as the ignition source of the

first explosion had been removed from a permissible scoop and was

located at a nonpermissible charging station.

The fatality for the 1987 Dutch Creek No. 2 ignition suffered

a myocardial infarction while fighting a fire resulting from the

ignition. The miner later died from a cardiac arrhythmia. A fatality

review committee decided the accident was chargeable to the

mining industry because the conditions surrounding the miner’s

fire fighting activities contributed to his death. The MSHA investigation report classified this accident as a fatal methane–air ignition.

Using Table A1 data, Figs. 1–5 show fatalities linked to different

locations and ignition sources. In Fig.1, the numbers of fatalities per

location were weighted by the uncertainty of the location of the

1989 Pyro No. 9 disaster. Of the ten 1989 Pyro fatalities, 5 were

attributed to a face ignition and 5 were attributed to an intake air

entry ignition. 71 of 160 fatalities were linked to intake air courses

using this weighting method (Fig. 1). Considering all fatalities from

the 1989 Pyro disaster, 76 fatalities were linked to intake air courses. In Fig. 2, numbers of fatalities per category were weighted by

ignition source uncertainties of the 1989 Pyro No. 9 disaster and

1987 Double R explosion. In Fig. 3, numbers of fatalities per category were weighted by ignition source uncertainties of the 1989

Pyro No. 9 disaster and 1987 Double R explosion. In Fig. 4, numbers

of fatalities per category were weighted by ignition source uncertainties of the 1983 McClure disaster and the 1987 Double R

explosion.

5. Discussion

5.1. Class I hazardous locations

Certain techniques are used to design electrical equipment to

protect against igniting explosions in locations where flammable

materials may be encountered under normal or abnormal conditions. These locations are classified as Hazardous locations

described in the National Electrical Code(NEC)

1

. NECArticle

500 describes Division locations, while AT:/PGN/ELSEVIER/JLPP/

22(1)/web/00002010/rticle 505 describes Zone locations (NEC,

2005). The requirements for Divisions and Zones differ somewhat

because the Division system was developed in the US while the

Zone system was developed in Europe. Zones were recognized in

the NECbeginning in 1996. NFPA 497 and NFPA 499 provide

guidelines for classifying Hazardous Locations.

One description of Class I Division 2 or Zone 2 is a location where

ignitable concentrations of gases or vapors are normally prevented

by positive mechanical ventilation, and which might become

hazardous through failure or abnormal operation of the ventilating

equipment (NEC 500.5(B)(2); 505.5(B)(3)). Division 2 and Zone 2

were established to allow the use of less expensive equipment and

less restrictive wiring methods as a more practical approach to

preventing explosions in locations that become flammable only

under infrequent, abnormal situations (Babiarz, 2004). Babiarz,

Delans, and Hughes (1997) conducted a survey that found Division

2 classified locations were by far the most common Hazardous

(classified) locations in North American industries at risk from

ignition of flammable materials, outside of the underground coal

mining industry. A rule of thumb for Division 2 or Zone 2 equipment is that it should not be an ignition source under normal

operation. Redundant safety features are generally not required.

The safety justification for the equipment is that the explosion

protection features are not likely to fail simultaneously with the Intake, 71

Face, 54

Sealed area, 12

Return, 12

Shaft, 8 

Longwall gob, 2

Highwall

opening, 1 

Fig. 1. 160 methane and/or coal dust explosion fatalities by location of the ignition

source in underground or high wall coal mines from 1976 to 2006. Numbers of

fatalities per location were weighted by the location uncertainty of the 1989 Pyro No. 9

disaster.

Nonpermissible

equipment, 

44.75 

Smoking 

materials, 30

Explosives, 20

Faulted

permissible

equipment,

17.25 

Torch or welder,

15 

Roof fall, 15

Lightning, 12

CM bits, 2

Blasting cap, 2

Messenger

wire, 2 

Fig. 2. Ignition sources linked to 160 methane and/or coal dust explosion fatalities in

underground and high wall coal mines from 1976 to 2006. Numbers of fatalities per

category were weighted by ignition source uncertainties of the 1989 Pyro No. 9

disaster and 1987 Double R explosion.

1 National Electrical Codeand NECare registered trademarks of the National

Fire Protection Association, Quincy MA.
infrequent process failure that releases the flammable material. The

less redundant or robust features of Division 2 or Zone 2 equipment

reflect the layer of protection already provided by the flammable

material containment or ventilation system to prevent the flammable atmosphere from contacting the electrical equipment.

Requirements for Division 2 or Zone 2 approved equipment imply

that when lives are at stake, a good ventilation system should not

be used in place of the protected equipment; rather, the protected

equipment is a necessary layer of protection along with the ventilation system.

One condition for Class I Zone 2 locations is that if a flammable

atmosphere is released, it will exist only for a short period (NEC

505.5(B)(3)). During mine emergencies, however, battery powered

equipment may be abandoned and exposed to methane for an

extended period of time. More stringent Class I Division 1, Zone 1 or

Zone 0 protection would therefore be necessary for battery powered equipment abandoned during a mine emergency. One

description of a Class I Division 1 or Zone 1 location is a location in

which ignitable concentrations of flammable gases or vapors can or

are likely to exist under normal operating conditions (NEC

500.5(B)(1); 505.5(B)(2)). Class I Division 1 overlaps with Zone 0,

which is a location where flammable gases or vapors are present

continuously or for a long periods of time (NEC 505(B)(1)).

The Hazardous Class refers to the flammable material; Class I

materials are flammable gases and vapors (NEC 500.5 (B)). Methane

is a Class I Group D (Division system) or Class I Group IIA (Zone

system) flammable material. Class I Group I (Zone system) refers to

firedamp, defined as a mixture of gases, composed mostly of

methane, found underground, usually in mines. NFPA 497 provides

guidelines for classifying flammable liquids, gases, or vapors.

5.2. Risk assessment for explosion protected equipment

A risk assessment approach for the acceptance of explosion

protected equipment has been introduced by the International

Electrotechnical Commission, Technical Committee 31 (IEC TC 31),

as an alternative method to the current prescriptive practice linking

equipment to Zones (IEC 60079-0). To facilitate this, a system of

equipment protection levels (EPLs) has been introduced to indicate

the inherent ignition risk of the equipment, no matter what type of

protection is used. For coal mining, EPL Ma refers to equipment

having a ‘‘very high’’ level of protection, which has sufficient

security that it is unlikely to become an ignition source, even when

left energized in the presence of an outbreak of gas. Typically,

communication circuits and gas detection equipment would be

constructed to meet the Ma requirements. EPL Mb refers to

equipment having a ‘‘high’’ level of protection, which has sufficient

security that it is unlikely to become an ignition source in the time

span between there being an outbreak of gas and the equipment

being de-energized. Typically all coal mining equipment would be

constructed to meet the Mb requirements, for example flameproof

motors and switchgear. EN 1127-2 describes basic explosion

prevention concepts for mining equipment used in Europe. EN 1710

notes that high energy mining equipment batteries cannot be deenergized when an explosive atmosphere occurs, and are ignitionprotected according to EN 60079-7 as type ‘‘e’’ – ‘increased safety

apparatus’. Groh (2004) explains ‘‘increased safety’’ among other

Nonpermissible

equipment, 13 

Lightning, 12

Torch, 8

Roof fall, 2

Explosives, 1

Fig. 5. Most likely ignition sources identified by MSHA for 36 fatalities from methane

and methane plus coal dust explosions in underground coal mines from 2000 to 2006.

Nonpermissible

equipment, 

44.75

Smoking

materials, 21 

Faulted

permissible

equipment, 0.25 

Messenger

wire, 2

Blast cap, 2

Roof fall, 2

Fig. 3. Methane and methane plus coal dust explosion fatalities linked to ignition

sources in intake air courses of underground coal mines from 1976 to 2006. Numbers

of fatalities per category were weighted by ignition source uncertainties of the 1989

Pyro No. 9 disaster and the 1987 Double R explosion.

Vehicle, battery

powered, 20.2 

Cable fault,

14.55

Vehicle, trolley 

wire, 5

Cable

connector, 2.3 

Power center,

1.7

Battery , 1

Fig. 4. Methane and methane plus coal dust explosion fatalities linked to nonpermissible electrical equipment in intake air courses from 1976 to 2006. Numbers of

fatalities per category were weighted by ignition source uncertainties of the 1983

McClure disaster and the 1987 Double R explosion.
explosion protection techniques for underground coal mining

equipment commonly used outside of the US.

5.3. Intake air course hazards

Fig. 1 shows that many US explosion fatalities since 1976 can be

linked to ignition sources in intake air courses. In all of these

accidents, the ventilation system failed or was found to be inadequate. These fatalities suggest intake air courses of gassy underground coal mines should be considered Class I Division 2 or Zone 2

locations at a minimum, i.e. locations in which flammable gases or

vapors are normally prevented by positive mechanical ventilation,

and which might become hazardous through failure or abnormal

operation of the ventilating equipment (NEC 500.5 (b) (2); 505.5

(b) (3)).

All intake air ignitions involved methane initially. The severity of

some of these explosions was enhanced by coal dust suspensions

after the methane was ignited. Equipment designed for methane

atmospheres would reduce the risk of fatal explosions compared to

the risk of using normally sparking equipment in intake air courses

of gassy underground coal mines. This does not preclude the need

to protect against hazards from coal dust layers that may accumulate on equipment or in entries, posing a fire hazard or explosion

enhancement hazard after the dust is entrained in the air. 30 CFR 75

subpart E addresses combustible materials and rock dusting. 30 CFR

75 subpart L addresses fire hazards. Direct ignition of coal dust

suspensions is a primary concern when using explosives. 30 CFR 75

subpart N addresses explosives and blasting.

Figs. 2 and 3 show that nonpermissible equipment can be linked

to more explosion fatalities than any other ignition source category,

for all locations, and especially in intake air courses. Fig. 5 shows

this trend continues to recent times. All of the nonpermissible

equipment ignition sources linked to explosion fatalities were

located in intakes. Fig. 4 shows that nonpermissible vehicles

(battery and trolley powered) were linked to most intake explosion

fatalities. Today, several underground vehicle manufacturers offer

explosion protected locomotives and personnel carriers, track or

tire, battery or diesel. Given the history of vehicle ignited fatal

explosions and the availability of explosion protected vehicles, use

of explosion protected vehicles in intake air courses of gassy

underground coal mines is recommended to reduce this hazard.

Twelve of the cable fault fatalities (Fig. 4) can be linked to the

damaged block light cable igniting the second massive Brookwood

explosion. The block light system was not required to be designed

to prevent methane ignition as it was installed in an intake air

entry. The description of the block light circuit (MSHA, 2002)

suggests the block light installation may not have met several

requirements for flexible cords in Class I Hazardous Locations

(2005 NEC 501.140; 505.17)2

. Potential violations involved: lack

of a separate grounding conductor, cord not listed for extra hard

usage, cord not protected from damage by location or suitable

guard. Compliance with these NECand OSHA requirements

might have prevented the 2nd 2001 Brookwood explosion

(Dubaniewicz, 2007).

30 CFR 75.323 directs workers to disconnect electrical circuits

at the power source when excess methane is present. Disconnecting circuits can produce an incendiary spark. Yet, explosion protected disconnects are not required in intake air entries

that may become flammable during emergencies, when the

ventilation system fails. Activation of nonpermissible circuit

breakers in power centers were implicated in the 1987 Double R

and 1983 McClure fatal explosions. The most likely ignition

source for the first 1976 Scotia explosion was arcing created by

the open type electric motor controller on the locomotive when

the controller was turned to the ‘‘off’’ position. Thirty years later,

a miner disconnected battery leads to a nonpermissible vehicle

during the early stages of the 2006 Sago disaster. This action was

prompted by a carbon monoxide alarm alerting the miner to bad

air. Even if a methane monitor alarm had sounded in this situation, a literal interpretation of 30 CFR 75.323 would have directed

this miner to disconnect the circuit in the presence of excess

methane. Shutting off a light switch in a faulted explosion proof

enclosure while evacuating during a methane outburst was the

likely ignition source for the 1981 Dutch Creek disaster, 15 killed.

Although the enclosure was faulted, this disaster is a horrific

example of the dangers of disconnecting unprotected circuits in

a flammable atmosphere. Inspection, maintenance, and repair of

explosion protected equipment are of paramount importance.

Explosion protection is recommended for all electrical disconnects in intake air courses that may activate automatically or be

activated manually in the presence of excess methane during

emergencies.

Most fatalities linked to cigarette lighters occurred when the

miner was lighting up in intake air courses (Fig. 3). Smoking

materials are prohibited in underground coal mines (30 CFR

75.1702). The smoking related fatal explosions emphasize the

hazard of open ignition sources located in intake air courses of

gassy mines should the ventilation system fail or become inadequate. The use of explosion protected electrical equipment in

intakes of gassy mines may make the miner more aware of ignition

hazards in these areas, including smoking materials.

5.4. Rescue team hazards

Rescue/recovery teams have encountered electrical ignition

sources, some with fatal consequences. An energized block light

circuit was the likely ignition source for the second 2001 Brookwood explosion, killing all of the rescuers. While recovering the

deceased miner from the 1987 Double R explosion, the recovery

team encountered an arcing cable connected to a battery. Following

the 2001 Brookwood disaster, the United Mine Workers of America

recommended rubber conduit be placed over battery charging

cables. This recommendation would have also applied 15 years

earlier to the 1987 Double R explosion. 1989 Pyro recovery

personnel encountered a faulted permissible battery powered

scoop tractor with a pump motor running. 2006 Sago rescuers

encountered a battery powered mantrip with lights on. Class I

Division 2 or Zone 2 techniques are not appropriate for circuits that

may be immersed in a flammable atmosphere for a long time

during a mine emergency. More stringent Class I Division 1, Zone 1,

or Zone 0 techniques are recommended for nonpermissible battery

powered equipment in intake air courses, to protect rescue and

recovery personnel.

6. Recommendations

Since 1976, many fatalities from explosions in gassy underground coal mines can be linked to ignitions in intake air entries,

when the ventilation system failed or was inadequate. The fatal

explosions ignited in intake air courses of gassy underground coal

mines involved only methane initially. The severity of some of these

explosions was enhanced by coal dust suspensions only after the

methane was ignited. The fatality data suggests intake air entries

that may become flammable should the ventilation system fail

should be considered Hazardous (classified) Locations per the

NEC, Class I Division 2 or Zone 2 at a minimum.

2 The 1999 NECwas in effect at the time of the Brookwood disaster. Requirements for flexible cords in Class I hazardous locations are found under Article

501-11 of the 1999 NEC.
Many fatalities from explosions ignited in intake air entries can

be linked to electrical equipment. Class I Division 2 or Zone 2

explosion protection techniques are recommended for nonpermissible equipment used in intake air courses so that it does not

present an ignition source under normal operation, before the

power source is removed in the event of an emergency. Nonpermissible equipment that is likely to remain energized during

emergencies, e.g. battery powered equipment, should be protected

by more stringent Class I Division 1, Zone 1, or Zone 0 techniques, to

protect rescue/recovery personnel. US mining industry participation with the IEC to develop a risk assessment approach for the

acceptance of explosion protected mining equipment is

recommended.

Of the nonpermissible equipment ignition sources, vehicles

were linked to most intake explosion fatalities. Use of explosion

protected vehicles in intake air courses of gassy underground coal

mines is recommended to reduce this hazard. Compliance with NEC

requirements for flexible cords in Class I Hazardous Locations is

recommended to reduce the ignition hazard of cable faults in intake

air courses of gassy underground coal mines. Explosion protection

is recommended for all electrical disconnects in intake air courses

of gassy mines that may activate automatically or be activated

manually in the presence of methane during emergencies.

Inspection, maintenance, and repair of explosion protected equipment are of paramount importance.

The smoking related fatalities emphasize the hazard of open

ignition sources located in intake air courses or other active

workings of gassy mines where miners are normally required to

work or travel.

Acknowledgements

The author thanks Melody E. Bragg, Technical Information

Specialist, Technical Information Center and Library, for providing

the MSHA fatal investigation reports released prior to 1995.

Appendix

Table A1

Fatal methane and/or coal dust explosions in underground and high wall coal mines

1976–2006

Year Operator, mine,

and state

Fuel Ignition

location

Ignition sources Killed

1976 Scotia Coal Co.,

Scotia Mine, KY

Methane Intake Normal arcing of

battery powered

locomotive

15

1976 Scotia Coal Co.,

Scotia Mine, KY

Methane &

coal dust

Face Roof fall onto

roof bolter

11

1977 P & P Coal Co., #2

mine, VA

Methane Return Cigarette lighter 4

1977 Bethlehem

Mines Corp.,

Revloc #32, PA

Methane Shaft Torch 1

1980 Westmoreland

Coal Co., Ferrell

#17 Mine, WV

Methane Intake Trolley wire

powered

locomotive

5

1981 Mid-Continent

Resources, Inc.,

Dutch Creek #1

Mine, CO

Methane &

coal dust

Face Faulted

explosion proof

enclosure on

continuous

miner (CM)

15

1981 Adkins Coal Co.,

#11 Mine, KY

Coal dust Face Detonation of

explosives

8

1981 Grundy Mining

Co., #21 Mine, TN

Methane Intake Cigarette lighter 13

1982 RFH Coal Co., #1

Mine, KY

Coal dust Face Detonation of

explosives

7

Table A1 (continued)

Year Operator, mine,

and state

Fuel Ignition

location

Ignition sources Killed

1983 Clinchfield Coal

Co., McClure #1

Mine, VA

Methane Intake Battery powered

track mounted

mantrip, power

center circuit

breaker, dinner

hole light

connection, cable

plug for CM

trailing cable,

belt control cable

disconnect or

fault, ground

fault in trailing

cable for

conveyor belt

feeder.

7

1983 Helen Mining

Co., Homer City

Mine, PA

Methane Intake Arcing controller

on vehicle

1

1984 Pennsylvania

Mines Corp.,

Greenwich

Collieries #1

Mine, PA

Methane Intake Normal arcing of

nonpermissible

battery powered

locomotive

3

1985 M.S.W. Coal Co.,

#2 Slope, PA

Methane Face Detonation of

explosives

3

1986 Pyro Mining Co.,

Pyro #9 Slope,

William Station

Mine, KY

Methane

and/or coal

dust

Face Detonation of

explosives

1

1987 Mid-Continent

Resources Inc.,

Dutch Creek #2

Mine, CO

Methane Face CM bits struck

sandstone roof

1

1987 Double R Coal

Co., #1 Mine, VA

Methane &

coal dust

Intake Two power

centers, battery

charging cable,

faulted

permissible

scoop.

1

1989 Pyro Mining Co.,

Pyro #9 Slope,

William Station

Mine, KY

Methane Face or

intake

Faulted

permissible

scoop at face,

torch or igniter at

face, blasting cap

in intake, roof fall

in intake,

messenger wire

tensile failure in

intake

10

1991 Fire Creek Inc.,

#1 Mine, WV

Methane Face Cigarette lighter

or match

2

1991 Addwest Mining

Inc., Watson

Bridge Mine, KY

Methane &

coal dust

Highwall

opening

CM bits struck

hard roof

1

1992 Consolidation

Coal Co.,

Blacksville #1

Mine, WV

Methane Shaft Welding sparks 4

1992 Southmountain

Coal Co., #3

Mine, VA

Methane &

coal dust

Intake Cigarette lighter 8

1993 A.A.&W. Coal Co.,

Elmo #5 Mine,

KY

Methane &

coal dust

Return Cigarette lighter 1

1994 Day Branch Coal

Co., #9 Mine, KY

Methane &

coal dust

Return Cigarette lighter 2

2000 Plateau Mining

Corp., Willow

Creek Mine, UT

Methane Unsealed

gob

Roof collapse

ignited 1st

explosion,

subsequent oil

and coal fire

ignitedmore

explosions

2

(continued on next page)
References

Babiarz, P. S. (2004). Cooper Crouse-hinds ex digest. Available from. <http://www.

crouse-hinds.com/crousehinds/sound_ideas/ex_digest_display.cfm>.

Babiarz, P.S., Delans, W.B., Hughes, R. (1997). Cable or conduit – who uses it and

why? Record of Conference Papers, Industry Applications Society 44th Annual

Petroleum and Chemical Industry Conference. Banff, Alberta September 15–17,

1997. IEEE Catalog No. 97CH36128, pp. 129–134.

Bethell, T. (April 1976). Scotia: a disaster that was no accident. United Mine Workers

Journal 11–24.

30 CFR. Code of Federal Regulations. Mineral resources, parts 1 to 199. Available

from. <http://www.msha.gov/30CFR/CFRINTRO.HTM>.

Dobroski, H., Jr., Stephan, C. R., & Conti, R. S. (1996). Historical summary of coal mine

explosions in the United States, 1981–1994. United States Department of the

Interior. Bureau of Mines Information Circular, 9440, 55.

Dubaniewicz, T. H., Jr. (2007). The Brookwood disaster and electrical requirements

for hazardous (classified) locations. IAS ’07: Conference Record of the IEEE

Industry Applications Conference, 42nd IAS Annual Meeting, New Orleans, LA,

September 23–27, 2007, Vol 4 (pp. 1–7). Piscataway, NJ: Institute of Electrical and

Electronics Engineers, Inc., Available from. <http://www.cdc.gov/niosh/mining/

pubs/pubreference/outputid2527.htm>.

EN 1127-2. (2002). Explosive atmospheres – Explosion prevention and protection –

Part 2: Basic concepts and methodology for mining. London: British Standards

Institution.

EN 1710. (2005). Equipment and components intended for use in potentially explosive

atmospheres in underground mines. London: British Standards Institution.

Groh, H. (2004). Explosion protection. Oxford, UK: Elsevier Butterworth-Heinemann.

Humphrey, H. B. (1960). Historical summary of coal mine explosions in the United

States, 1810–1958. United States Department of the Interior. Bureau of Mines

Bulletin, 586.

IEC 60079-0 Ed 5.0: Explosive atmospheres – Part 0: Equipment – General requirements. (2007). Geneva. Switzerland: Annex D. International Electrotechnical

Commission.

MSHA. (2002). Report of investigation, fatal underground coal mine explosions,

September 23, 2001, No. 5 Mine, Jim Walter Resources, Inc. Alabama. CAI-2001-

20 through 32. U.S. Department of Labor, Mine Safety and Health Administration. Available from. http://www.msha.gov/FATALS/2001/jwr5/jwr5home.

htm.

MSHA. (2007). Fatal alert bulletins, fatalgrams, and fatal investigation reports. U.S.

Department of Labor, Mine Safety and Health Administration. Available from.

http://www.msha.gov/fatals/fab.htm.

NEC. (2005). Articles 500–505. NFPA 70: National Electrical Code, International

Electrical Code Series. Quincy, MA: National Fire Protection Association.

NFPA. (2004). NFPA 497 recommended practice for the classification of flammable

liquids, gases, or vapors and of hazardous (classified) locations for electrical

installations in chemical process areas. Quincy, MA: National Fire Protection

Association.

NIOSH. (2007). MSHA data file downloads. NIOSH Mining Safety and Health Research.

Available from. http://www.cdc.gov/niosh/mining/data/.

Richmond, J. K., Price, G. C., Sapko, M. J., & Kawenski, E. M. (1983). Historical

summary of coal mine explosions in the United States, 1959–81. United

States Department of the Interior. Bureau of Mines Information Circular IC,

8909.

UMWA. (2003). Jim Walter resources #5 coal mine disaster, September 23, 2001;

A united mine workers of America report. UMWA Department of Health

and Safety. Available from. <http://www.umwa.org/brookwood/brookwood.

shtml>.

USMRA. (2007). Scotia mine. Uniontown, PA: US Mine Rescue Association. Available

from. <http://www.usmra.com/saxsewell/scotia.htm>.

Table A1 (continued)

Year Operator, mine,

and state

Fuel Ignition

location

Ignition sources Killed

2001 Jim Walter

Resources Inc.,

#5 Mine,

Brookwood AL

Methane Intake Battery assembly

removed from

scoop and

damaged by roof

fall

1

2001 Jim Walter

Resources Inc.,

#5 Mine,

Brookwood AL

Methane &

coal dust

Intake Damaged block

light cable

12

2003 McElroy Coal Co.,

McElroy Mine,

WV

Methane Shaft Cutting torch 3

2006 International

Coal Group, Sago

Mine, WV

Methane Sealed

area

Lightning 12

2006 Kentucky Darby

LLC, Darby Mine

#1, KY

Methane &

coal dust

Return Torch 5

2006 R&D Coal Co., PA Methane Face Explosives 1

Total 160