on sections A and B indicated the movement of
methane was away from the faces and toward the
fan. Data from the two locations sampled on section
A and the three locations sampled on section B are
included in Figure 4. As noted in Figure 1, the meth-
ane levels began to decrease at the face almost as
soon as the fan was restarted. Twenty to thirty min-
utes later there was an increase in methane concen-
tration at the immediate return locations, about 100
ft outby the face. Concentrations in the main return
of section B, 300 ft outby the face, increased about
90 minutes after the fan was restarted.

Fan Off

2
2
as 20
$ ion B
é2 ,, Section
10
05
i.
o
7:00 AM 10:00AM 1:00 PM 4:00 PM
Time, min

Figure 4. Methane concentrations measured on sections A and
B.

Although there were no significant accumulations of
methane along the haulageways during the fan shut

653

down, methane did accumulate near the work faces
and at sampling Location 7, positioned adjacent to a
haulageway. The effect of these accumulations on
worker safety during the time of mine evacuation
appeared to be minimal.

Many different factors can cause methane levels
in mines to vary. The information obtained during
these underground studies only applies to the mines
where the studies were conducted. Any changes in
operating conditions that might affect mine ventila-
tion (such as localized atmospheric phenomena)
could periodically affect methane levels at any one
mine. The effects of ventilation changes on methane
levels in particular mines can be determined only by
additional site-specific research.

Methane concentrations must be measured during
a fan stoppage to evaluate the potential risk to work-
ers exiting the mine via powered haulage while the
fan is not operating. Methanometers with the capa-
bility of recording data must be used since the in-
struments must be placed in the mine before and af-
ter the fan stoppage. Ventilation conditions are
continuously changing in a mine and the measure-
ments taken are valid estimates of methane concen-
tration only for the conditions existing at the time of
the study.

For these tests selection of sampling areas was
based primarily on the experience of mine person-
nel. When developing a test plan for monitoring
methane concentrations along haulageways it is rec-
ommended that government enforcement and local
mine safety personnel be consulted.


‘Section B 0.20
15,
we 10 iH 0.15
$5 H 2
8£ os 4 £
So -_ 2
ae , cs E 0.10
2
7:00 AM 10:00AM 1:00 PM 4:00 PM 8
Time, min © 015 “o-oo
tee 0046063
Figure 2. Face concentrations at Mine 2. , ee Se i
Methane concentrations increased at the working o 20 40 60 80

faces in Mine No. 2 (locations 8 and 10) when the
fan was shut down. The increases varied from 0.4 to
1.2 pet. After the mine fan was restarted, concentra-
tions decreased quickly to levels measured prior to
the fan stoppage. Figure 2 shows the variation in
methane concentrations measured near the two faces
(Sections A and B) in Mine No 2.

The results of bottle samples collected in the
main fan exhaust at each of the four mines during
the first hour following fan restart are shown in Fig-
ure 3, Methane levels varied between mines but the
concentrations at each fan increased gradually at all
mines following the fan restart. Within an hour the
fan methane concentrations at all four mines had de-
creased to levels close to those measured before the
fan was stopped.

5 DISCUSSION AND CONCLUSIONS

Studies were conducted in four underground mines
to evaluate methane levels along haulageways dur-
ing planned stoppages of the main mine fans. In
three of the four mines there were no increases in
methane levels along the haulageways while the fan
was off. Liberation rates were very low in each of
the four mines.

The highest methane concentrations measured
during the fan stoppage studies were in Mine No. 2.
In Mine No. 2, methane increased by 0.1 pet in one
area (Location 1) and 0.7 pet in another (Location
7). Again, these values were well below the LEL for
methane. Locations 1 to 7 were on track haulage
routes that would be used by miners traveling from
sections A and B to the mine portal. Location 7 was
a bleeder evaluation point located close to the track.
The remaining sampling locations (8 to 12) were in
the active working sections designated A and B. At
locations 8 and 10 the methanometers were located
within 10 ft of the face. At locations 9 and 11 the
methanometers were in the immediate return entries
within 100 ft of the face, and location 12 was in the
main section return within 300 ft of the face.

The information obtained during the study at
Mine No. 2 was evaluated to determine the relative
risk associated with using powered haulage to re-

652

Time from restart, min
Figure 3. Methane concentrations in fan exhaust after restart.

move workers from the mine during a fan shutdown.
As seen in Figure 1, methane concentrations on the
sections began to increase at the active mining face
almost as soon as the fan was turned off. If the min-
ers would have left sections A and B 15 minutes af-
ter the fan was shut down, the highest methane con-
centrations measured at the two faces would have
been 0.2 and 0.4 pet respectively. Assuming the
miners would reach the portal by powered haulage
less than 1 hour after the fan stops, the highest meth-
ane concentration encountered along the haulageway
would have been 0.2 pct at location 1, as shown in
Table 1. Since, the potential for a frictional ignition
is related to the methane concentration, the risk to
safe egress via powered vehicles is obviously very
low. In fact, at Mine 2 the risk to miners due to the
exposure to methane during powered haulage
evacuation should be no greater than for miners
working at the mining face.

Although methane concentrations increased
slightly at some locations during the fan shut down,
the levels remained well below the LEL. If the dura-
tion of the fan stoppages was longer, the methane
concentrations may have continued to increase.
However, at all the mines surveyed there would have
been sufficient time (3 to 5 hours) for the workers to
evacuate the mine before methane concentrations
along the haulageways exceeded 0.2 pet.

Methane concentrations measured in all four
main fan exhausts increased after the fan was re-
started. This was due to methane that had accumu-
lated throughout the mine during the fan stoppage.
The amount of gas accumulated during the stoppage
depends on the liberation rate in the mine and the
time the fan was off. For mines 1, 2, 3 and 4, the ac-
tual times the fans were off were 5, 4, 3, and 5
hours. Since concentrations in areas sampled along
the haulageways did not increase significantly dur-
ing the time the fan was off, gas levels must have in-
creased in other mine areas. Most likely methane
levels rose in face areas, at bleeder evaluation points
and in return entries. In Mine No. 2, after the fan
was restarted, the methane concentrations measured


Mine Ventilation, De Souza (ed.)
© 2002 Swets & Zeitlinger, Lisse, ISBN 90 5809 387 5

Safety concerns associated with the use of electrically powered haulage
to remove workers from mines during main fan stoppages

C.D. Taylor, R.J. Timko, E.D. Thimons & J.A. Zimmer
Center for Disease Control and Prevention, NIOSH, Pittsburgh Research Laboratory, Pittsburgh, PA, USA

ABSTRACT: The roles of main mine fans in underground mines are to induce airflow and continuously re-
move hazardous gases and dust. While most larger mines use multiple fans to accomplish these tasks, many
smaller mines employ only a single fan. This paper concentrates on those mines having only one fan to pro-
vide ventilation needs. If this fan should cease to function, it is likely that methane concentrations will in-
crease in some areas of the mine. As a safety precaution, Federal Regulations require that personnel must be-
gin evacuating the mine within fifteen minutes after fan stoppage. Powered haulage can be used to transport
workers to the mine portal as long as travel is through areas where hazardous levels of methane are not ex-
pected. To determine where methane will accumulate along haulageways during a fan stoppage, air samples
must be taken at specific areas and analyzed for hazardous gases.

During this study, procedures were developed for measuring methane levels along haulageways that are
used to exit a mine following stoppage of the main mine fan. Methane levels were measured in four different
mines at selected underground locations during four planned fan stoppages. In these mines the measurements
taken only at the specified locations showed that, if workers had used electrically powered haulage to exit the
mine following a fan stoppage, the methane accumulated along haulageways during fan stoppages would not
have significantly increased the risk of an ignition.

1 BACKGROUND lation of the mine is interrupted, the mine foreman
shall order the power to be disconnected from the af-
fected portions and withdraw the men immediately
from the face areas. If the fan has been stopped for a
period of time in excess of fifteen minutes in a gassy
mine, the mine foreman shall order the men with-
drawn from the mine.

Following a withdrawal order, two methods of

An entry in an underground coal mine through
which equipment, personnel and, in some instances,
coal are transported is called a haulageway. This en-
try is always ventilated by intake or fresh air. If trol-
ley wires are located within the haulageway, the air
velocity through that entry is limited to 250 ft/min,

unless mine personnel are unable to keep methane
levels below one percent. If, during an underground
emergency, a mine evacuation is ordered, haulage-
ways become escapeways. Because they are venti-
lated by fresh air, these entries are usually the most
direct paths out of the mine.

Federal regulation 30 CFR 75:313 requires that, if
a mine fan stops and ventilation is not restored
within 15 minutes, all persons must be withdrawn
from the mine. In addition, all underground electri-
cal circuits must be de-energized. However those
circuits required to assist miners evacuating the mine
may remain energized if they are located in areas or
haulageways where methane is not likely to migrate
or accumulate. Section 221 (d) of the Bituminous
Coal Mining Laws of Pennsylvania requires that in
case of accident to a ventilation fan or its machinery,
or if the fan stoppage is planned whereby the venti-

649

escape are typically available to miners; ride out in
an available vehicle or walk out. In most mines, the
fastest way for workers to reach the shaft or portal is
by using powered haulage. Ideally, the time required
to ride out depends only on the distance of the work
location from the surface and the speed of the vehi-
cle, Elapsed time is often increased because of traf-
fic in the entry. The time required for workers to
evacuate on-foot depends on several factors, includ-
ing, once again, the distance of the work location
from the surface, the height of the coal seam and the
general condition of the haulageways. In addition,
the physical condition of the miners, including their
age, endurance and mobility, affects how quickly
they can reach the shaft or portal. It is the overall ef-
fect of these factors that determines worker safety
during evacuation from the mine.


In most coal mines located beneath the water ta-
ble, methane liberation is a continuous process.
Whenever the mine fan stops, methane concentra-
tions are expected to increase in some areas of the
mine. If the concentration of methane exceeds its
lower explosive limit (LEL), normally considered to
be 5 pct in air, the potential for an ignition and ex-
plosion becomes real. Removing workers from the
mine as quickly as practical following a fan stop-
page reduces the chances of injury or death should
an ignition occur.

Haulageways are always intake or fresh air en-
tries. Most mines have little data available to iden-
tify specific areas where methane concentrations
could be of concern, especially when fan operation
is interrupted. If engineers did take samples in a
haulageway, those readings would most likely be
obtained while the fan was operating. These samples
would not necessarily be indicative of high methane
concentration areas when the fan was not operating.

Using electrically powered vehicles to remove
workers from the mine during a fan stoppage as-
sumes that methane levels along haulageways are
not yet high enough to present an ignition risk. Al-
though the highest methane levels along haulage-
ways are normally expected in “high points,” areas
adjacent to abandoned workings, or areas not swept
by ventilating air flow, these values are normally
well below the LEL. In fact, 30 CFR 75:327 requires
that the methane concentration in trolley haulage-
ways always be less than one percent. However,
while there are regulations that specify the proce-
dure, location and instrumentation for monitoring
methane at the mining face, no similar regulations or
guidelines are available for making methane meas-
urements along haulageways.

The objectives of this work were twofold. First,
researchers wanted to provide guidelines for moni-
toring methane levels along haulageways. This in-
cluded identifying instrumentation needed for data
collection, determining the areas along haulageways
where methane is most likely to accumulate, and de-
ciding on locations in each area for positioning the
methanometer to insure representative readings.
Second, mine personnel and researchers wanted to
conduct methane sampling during planned mine fan
stoppages. The purpose was to demonstrate the pro-
cedures necessary for measuring methane concentra-
tions, and evaluate the potential risk factors associ-
ated with using electrically powered haulage to
remove workers from the mine during a fan stop-

page.

2 TEST PROCEDURES

2.1 Sampling instrumentation

Four different methanometers, obtained from three
manufacturers, were used during the underground

tests to monitor gas along the haulageways. Sensors
in three of the methanometers employed catalytic
heat-of-combustion detectors while the fourth used
an infrared sensor. Each methanometer was 1) ap-
proved by MSHA for use underground (intrinsically
safe), 2) battery operated, 3) portable enough to be
carried to each of the sampling areas, and 4)
equipped with a data recording (logging) device.

In three methanometers the data loggers were lo-
cated internally to the instrument; the fourth logger
was connected externally to the methanometer.
These loggers recorded methane concentration data
for either 30 or 60-second time intervals.

To determine methane concentrations at the mine
fan, air samples were taken just outby the fan. These
were collected by inserting a 20-ml, 96 pct-air-
evacuated glass test tube into a plastic plunger. This
assembly was similar to a device used to extract
blood for clinical testing. A hypodermic needle was
attached to the inside of the plunger. As the tube was
moved into the plunger the needle punctured a rub-
ber bladder at one end of the test tube. The pressure
difference between atmospheric and the inside of the
test tube caused an air sample to enter the tube. Pull-
ing the test tube from the plunger resealed the rubber
bladder and prevented the gas sample from escaping
or being contaminated. These samples were then re-
turned to the laboratory and analyzed for methane
content using gas chromatography (GC). The accu-
racy of the GC instrument is about 1 ppm or 0.0001
pet.

2.2 Sampling locations

Certain guidelines were applied to prioritize poten-
tial areas where methane was most likely to accumu-
late. Guidelines for likely sampling locations in-
cluded those near high points in the roof that were
due to, for example, a fall of roof, an old overcast
area, the inclination of a seam, or a fault zone. Pre-
ferred sampling locations were also in areas where
air velocities were lowest, and areas proximal to
mined-out workings that continue to be ventilated,
or near sealed old workings or gob areas.

In the four underground studies, methane samples
were taken at underground locations and on the sur-
face just outby the main mine fan. Based on their
experience and our guidelines, mine officials se-
lected the haulageway sampling locations in all four
tests. Most of the haulageway locations were along
routes taken by miners traveling between the work-
ing sections and the surface. Other selected loca-
tions, such as bleeder evaluation points, were near
the haulageways. NIOSH researchers determined the
remaining underground locations. These were at the
working faces and in the returns of active sections.
Researchers also obtained gas samples at the main
mine fan prior to fan shutdown and again following
fan restart.

650


To obtain the best estimate of the highest meth-
ane concentration at a specific location, researchers
wanted to optimize methanometer positioning rela-
tive to the entry geometry. At each location a
methanometer was positioned as close as practical to
the rib-roof intersection but not closer than one foot
from the rib or roof. Mine officials found locations
where ventilation airflow velocities were minimal.
Finally, locations were selected that were near to and
above trolley wires.

3 METHANE SAMPLING

3.1 Underground

Studies to measure methane levels during planned
mine fan stoppages were conducted in four mines.
Each mine had requested that NIOSH researchers
conduct a survey to evaluate the effects of a main
mine fan stoppage on methane levels along haul-
ageways. Entries to each of the four mines consisted
of a slope, two drift portals and one shaft.

NIOSH researchers visited each mine prior to the
day of the fan stoppage. Researchers traveled under-
ground, inspected each sampling area and decided
on the best methanometer sampling location. On the
morning of the survey, approximately one hour be-
fore the mine fan was shut down, researchers and
mine personnel positioned and started methanome-
ters at each location. Once all instruments were in
position and operating, everyone evacuated the mine
and the fan was shut down. Total time the fans were
turned off varied from about three to five hours. Af-
ter the fan was restarted and the mine re-inspected,
the instruments were brought to the surface by mine
personnel. The methane concentration data was re-
trieved from each data logger using software pro-
vided by the manufacturers. Spreadsheets were cre-
ated to chronicle the data. Graphs were then derived
to enable researchers to view the results.

3.2. Surface

To determine methane concentrations being ex-
hausted from the mine before the fan was stopped
and again following fan restart, air samples were
taken just downstream of the main mine fan evasé.
Evacuated test tubes were used to collect and pre-
serve the air samples. One sample was taken before
the fan was shutdown. Following the fan restart,
samples were obtained every five minutes for one
hour. As previously described, the sampling tubes
were then returned to the laboratory for analysis. GC
results provided the concentrations for all major at-
mospheric gases including carbon monoxide, and
hydrocarbons from methane to pentane.

4 RESULTS

In each of the four mines evaluated, methane con-
centrations were monitored continuously at five to
ten locations along the haulageways. Methane meas-
urements were also made in areas near one or two of
the active working faces. In three of the mines,
methane concentrations along the haulageways re-
mained at or below the detection limit of the
methanometer for the entire time the fan was shut
down. At the fourth mine, with the exception of two
locations, all other readings along the haulageways
remained zero.

Mine No. 2 results are included in this report as
an example of the data that researchers obtained
from these evaluations. The fan was turned off at
Mine No. 2 for approximately three hours. A sche-
matic of the areas sampled at Mine No. 2 is shown
in Figure 1. The initial and final methane concentra-
tions at the locations along the haulageways and on
the sections are given in Table 1. The methane in-
crease to 0.2 pct at Location 1 was not readily ex-
plainable. The increase to 0.7-pct methane at Loca-
tion 7 was most likely due to the location’s
proximity to a bleeder evaluation point.

Table 1. Mine No. 2 methane concentrations.

[Haulageway Methane Concen- |Section Methane Concentra-
trations, (%) CH, tions, (%) CHy
[Fan Re- [Fan [Fan Re-
{Location |Fan Stop]start Location |Stop__|start
T. for Joa 8. [0 loa
2. [0.0 0.0 9. for [1.0
B. CO (0) 10. lor |i3
a. [0.00.0 mn lor [13
5. fo.0 [0.0 12. loo [oa
6. lo.0 [0.0
7. loo 0.7

651

key

yy
‘© Sampling unit
Section B

Figure 1. Areas sampled at Mine 2.