ADVANCES IN MINE EMERGENCY COMMUNICATIONS 

Jeff Kravitz 

Mine Safety and Health Administration 

Pittsburgh, PA 15236 

John Kovac and Wayne Duerr 

U.S. Bureau of Mines 

P.O. Box 18070 

Pittsburgh, PA 15236 

ABSTRACT 

Since 198 1, Federal mining Iaw has required 

every miner working in underground coal mines 

to have a self-contained, self-rescuer (SCSR) 

available for use in emergencies. Some miners 

that have escaped from fires using SCSR's have 

reported that they had to remove their mouthpiece 

to talk during escape, thus compromising the 

protection afforded by the SCSR. If miners are in 

thick smoke during an escape, they may have 

troubie if they become separated from their group. 

The visibility can be so poor that separation can 

occur at very short distances. To address this 

problem, two-way, FM radios were built into the 

SCSR to improve the ability to cortlmunicate 

should the miners be separated over relatively 

short distances. 

The SCSR prototypes built and used in 

testing included both two-way radios and 

improved mouthpieces. Comparison studies were 

conducted using combinations of the new and oId 

mouthpieces, and trials using the radio or not 

using the radio. Subjective judgements indicate 

that communication ability was significantly 

improved using the protowp devices. 

Communication problems have been 

encountered with teams using standard voicepowered communications systems. Mine rescue 

teams perform rescue and recovery work under 

extremely hazardous conditions, life lines are a 

standard part of mine rescue team equipment. 

Leaky feeder and quasi-leaky feeder life line 

communications systems provide significant 

improvements over standard systems. These 

improved systems aIlow all members of the team 

to communicate with each other and their base of 

operations. These innovations will significantly 

enhance the safety of mine rescue operations. 

INTRODUCTION 

Since 1981, Federal mining law has required 

every miner working in underground coal mines 

to have a self-contained, self-rescuer (SCSR) 

available for use in emergencies. These devices 

provide a minimum of one hour of oxygen to 

escaping miners in the event of an emergency 

evacuation due to mine fires or explosions. 

Miners that have escaped from several recent 

mine fires using SCSR's have been interviewed, 

and some have reported that they had to remove 

their mouthpiece to talk during escape, thus 

compromising the protection afforded by the 

SCSR. 

In September 1989, an explosion occurred at 

the Pyro Mining Company's No. 9 Slope, William 

Station Mine in Union County, Kentucky, 

resulting in the deaths of ten underground coal 
miners. Five of the nine persons who used filter- I I 

type self-rescuers (FSR's) while trying to escape 

the explosion area did not survive. According to 

the survivors, several of the victims removed their 

self-rescuers in an attempt to talk with each other. 

As a result of this incident, an MSHA report 

(1990) recommended that MSHA, in conjunction 

with the U. S. Bureau of Mines, should examine 

the feasibility for developing self-contained selfrescue devices which allow communication 

without removal of the mouthpiece. 

Successful communication is critical during 

an emergency evacuation. Miners need to be able 

to communicate during escape in order to make 

decisions and to provide emotional support to one 

another in a life threatening situation. This 

requires a full range of two way speech. 

Simplified communications, such as cap lamp or 

hand signals, simply do not begin to provide the 

necessary psychological support, and decision 

making ability needed during a crisis. 

SCSR Communication Problems and Solutions 

The main problem in trying to communicate 

while wearing an SCSR is the mouthpiece. It 

interferes with normal speech in ways that are 

difficult to compensate for. The teeth and lips 

can not be brought together as they are in normal 

speech. This interferes particularly with words 

that contain "mu or "b" sounds. An improved 

mouthpiece was developed which helps to 

overcome the interference. Figure 1 is a 

photograph of the improved mouthpiece that was 

developed during a one year research effort. A 

speech pathologist and an oral surgeon were 

included in the team that designed the new 

mouthpiece. This part is more pliable, and 

considered by some using it, to be more 

comfortable. If miners are in thick smoke during 

an escape, they may have trouble if they become 

separated from their group. To address this 

problem, two-way, FM radios were built into the 

SCSR to improve the miner's ability to 

I I 

Figure 1.--New mouthpiece (left) vs standard 

mouthpiece 

communicate at a distance. The effective range 

of this system is currently about 30 meters. 

Communication at this range without the radio is 

virtually impossible, with or without the improved 

mouthpiece. Figure 2 is a schematic diagram of 

an SCSR equipped with radio communications. 

Subjective judgements indicate that 

communication ability is significantly improved 

using the prototype devices. It is still difficult to 

talk with the SCSR on; however, the situation is 

improved from the unmodified rescuer. Further 

studies will focus upon repackaging and 

improving the radios, and performing objective 

tests of speech clarity. 

Life Line Communications Problems and 

Solutions 

Mine rescue teams perform rescue and 

recovery work under extremely hazardous 

conditions. Federal law requires each operating 

mine to have ready access to at least two certified 

mine rescue teams. Only highly trained and 

motivated persons are permitted to work on these 

teams due to the demanding nature of their 

operations. Becoming separated from the team in 

limited visibility could be a fatal mistake when 

there is no other way to re-establish 

communications. Therefore, life lines are a 
Ear-bud microphone 

Ear-bud speaker 

\ 

I -m/ \ Mouth microphone 

SCSR Simulator 

Figure 2.--Schematic of communications 

equipped SCSR 

standard part of rescue and recovery operations. 

The type of life line used by the majority of mine 

rescue teams is a 300 meter section of a relatively 

thick cable that supports a sound-powered 

communications system. This cable is fed off a 

cable reel as the team advances. It is 

cumbersome to handle, often gets caught on 

obstacles, such as mining equipment, and it is 

difficult to pull over such equipment or around 

coal pillars (blocks of coal left during the mining 

operations to help support the mine roof). This 

type of communications system only allows one 

member of the team (the communications officer) 

to talk back to his base of operations (the fresh 

air base). 

Standard leaky feeder cable systems have 

previously been investigated for use in mine 

rescue communications. Such systems were 

found to be too rigid and heavy. Mine rescue 

communications, however, could , in fact, benefit 

from the properties of a leaky feeder system. 

Such a system would allow all team members to 

talk to each other and the fresh air base. 

to the others in the group along an established 

search path. Thus the range limitations of leaky 

feeder cable fall within boundaries that are 

already established by safety considerations. 

Description of Equipment Used 

A communication test was set up in the 

Bureau's Safety Research Coal Mine at Bruceton, 

PA, using Motorola MX330 hand-held radios, 

Radio Shack RG8 coaxial cable, and a yagi 

antenna. One of the radios was connected to the 

RG8 cable by an external antenna jack. The other 

two hand-held radios were operated without any 

physical connection to the cable. The RG8 cable 

acted as a quasi-leaky feeder. 

The MX330 is an MSHA approved radio that 

can be used in explosive atmospheres. For the 

test, the radios were equipped with a remote 

microphone and a replaceable, approved, 3-hour, 

ni-cad battery. The radios operated on 464.5- 

469.5 MHz. The RG8 cable was divided into 

three, 75 meter sections, two 15 meter sections, 

and one 45 meter section to evaluate the 

convenience of carrying. Each end was equipped 

with an "N" type connector. The "N" type 

connector was selected because it makes a secure 

connection. It is screwed together and is water 

resistant. At each joint a "T" connector could be 

placed to allow for branching. The yagi antenna 

was placed on the end of one of the branched 

sections. The radios can be damaged by 

insufficient impedance in the antenna circuit. The 

yagi antenna provides this impedance load in 

addition to its broadcast function. Figure 3 is a 

schematic diagram of the equipment used during 

the in-mine tests of this system. 

Since the mine rescue team members are Results 

dependent upon their self-contained, breathing 

apparatus (SCBA) for survival, they cannot launch The radios were taken into the mine to test 

individual expeditions far afield from the rest of the range without the assistance of the RG8 cable 

the team members. The only margin of safety and antenna. The communications were clear and 

that can be provided comes from remaining close understandable as long as line-of-sight was 
RG - 8 Cocodal Cable 

N Type T connector 

(Only when using osecond attenna) 

-1- 

I Yogi Antenna I 1 I 

Figure 3.--Schematic of leaky feeder system 

maintained between radios. Once line-of-sight 

was lost, the reception can be broken in as little 

as 6 meters from the line of sight. 

In the next test situation, a single 75 meter 

length of cable was connected to the radio and the 

yagi antenna was connected to the end of the 

cable. This combination seemed to increased the 

effective distance in two ways. Not only was the 

distance between the two radios increased by the 

length of the cable, but the yagi antenna was a 

more efficient broadcast sourcelreceiver than the 

built-in antenna. It was also found that the cable 

needed to by hung from the rib and not left lying 

on the mine floor in order to achieve acceptable 

results. 

In the succeeding trials, the antenna was 

placed progressively closer to the base end of the 

cable as additional cable was added. The effect 

of adding cable was to reduce the signal strength 

at the remote antenna. 

The final layout consisted of 225 meters of 

cable with the yagi antenna placed 75 meters 

from the base unit. In this configuration, 

cornmuni'cation away from the antenna, could be 

maintained as long as the cable was in the same 

entry as the remote radio. In this arrangement, 

effective signal strength was lost within 

approximately 6 meters of the end of the cable, 

even when line-of-sight was maintained. 

Future Work 

Additional parts were obtained to adapt the 

remote microphonelspeaker units to the facepieces 

of the breathing apparatus used by most mine 

rescue teams. A final demonstration project will 

be conducted during a rnine rescue exercise. 

Conclusion 

Two advances in mine emergency 

communications have been achieved. Prototypes 

have been built and tested; however, further 

testing, repackaging, and improvements must 

occur before both devices are made available to 

the mining industry. 

Improvements necessary to complete the 

SCSR communications system are: 1) 

improvements in the radio, 2) miniaturization of 

the electronics packages, and 3) the electronics 

package must be made permissible (intrinsically 

safe or explosion proof, to be allowed to operate 

in an explosive methane-air environment). 

Improvements necessary to complete the life 

line communications system include: 1) choosing 

an optimal frequency for operation, 2) making a 

final selection on a quasi-leaky feeder cable, 3) 

choosing optimal interfaces for SCBA devices, 

and 4) making the system permissible. 

This technology will significantly enhance 

the safety of rnine rescue operations. It possesses 

the potential of allowing rescue teams to operate 

more efficiently. The combination of security and 

increased efficiency should also allow for the use 

of fewer teams in some circumstances thus further 

reducing exposure to very hazardous 

environments.