CHAPTER 6: RISKS ASSOCIATED WITH THIN SEAM MINING.

At Dorstfontein Mine all of the mining has taken place in seam heights exceeding
1.5m. The risks and associated mining problems identified during the life of the mine
were discussed in Chapter 4 and differ from that identified by Clarke et al. (1982) for
very thin seam mining. This chapter discusses the risks as well as the health and
safety issues associated with thin seam mining (at Dorstfontein below 1.4m heights).
Although some of these risks may be more applicable to hand-got coaling, they may
not be omitted as although continuous miners replaced the pick and shovel, people
still work and move around in these thin seam CM-sections.

6.1. Geological.
a.) Seam heights. One of the greatest risks in thin seam coal mining is
unexpected decreases in the already thin seam height. These
changes are unpredictable and may be attributed to various factors
for example floor rolls and slumping structures in the roof. These
kind of geological features could bring a section to a standstill.
b.) Quality changes. In Chapter 3 it is apparent that the coal quality
and product yield of the thin seam areas could be extremely
good. Unexpected changes in product yield may increase costs,
and might terminate this difficult way of mining. The sulphur
content is one of the most important quality parameters that
must be monitored carefully. Coal analysis has showed that in
some areas the sulphur tends to be high due to free pyrite in the
coal seam. An increase in the sulphur content, outside the
product specifications, would create a problem on the marketing
side.
c.) In-seam partings. Throughout all the exploration programmes
there were few in-seam partings intersected. This does not
exclude the possibility that extra thin shale bands and flood
sheets may occur. This will reduce the yields and create
problems fqr continuous miner production.

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 d.) Change of parting lithology. The seam-split parting will form the
roof of the thin seam section and exploration has shown that
this parting has an upwards-coarsening sequence with a lower
section of interlaminated sandstone and siltstone. This parting
can be supported, as tests have shown, as long as it stays
upwards coarsening. Changes in the laminations of this parting
may render it a dangerous roof and create production- and yield
problems.
e.) Water. Excessive discharge of water from either the coal seam,
overlying roof strata or dyke developments would create
problems for people working in such conditions. The thin seam
does not allow ease of movement and in the event of excess
water people would get wet which will lead to health problems.
Excess water would also enter machinery and motors and result
in breakdowns. Slippery working conditions would lead to
injuries.
f.) Unpredicted dykes. Most of the dykes in the thin seam area
have been predicted and some of them were intersected during
the South Main development. In the unlikely event that some
unpredicted dykes do occur it will create a serious problem for
production and could result in adverse roof conditions. Some
dykes discharge a great amount of water, which could lead to
mining problems and health and safety issues.

6.2. Mining Accidents.

An accident has been defined as "any unplanned exchange of energy
which degrades the system in which it occurs". The effect of an accident
on mine personnel is the most noticeable and the recording of such
injuries provides the bulk of the statistical information on accidents. In
most countries this wider concept of an accident is reflected in mining
legislation that demands more records and reporting of certain
dangerous occurrences that mayor may not cause personal injury. The

72
major factor in determining whether an accident is recorded and
reported is the nature of the injury sustained. That is the effect in terms
of disability and the time the injury prevented the person from working
(Clarke et aI., 1982).

In the United States a relatively low number of incidents were reported

in thin seam coal mining. There was no significant variation of the
frequency of fatalities between thick and thin seam mining. The average
rate for accidents was higher for thin seams than for medium to thick
seams. The frequency rate of disabling injuries was approximately 100
times higher than the fatality rate. It was found that the accident rate
was significantly higher in the thin seams than in the thicker or medium
seam mines. The increase in the level of hazards may be explained by
the decrease in lighting and comfort in thin seam working conditions. In
the case of injuries from falls of roof, it was suggested that it was more
difficult to avoid an imminent fall in the more cramped conditions of the
thin seam. Another possible explanation was the lack of protective cabs
and canopies on thin seam face equipment (Clarke et aI., 1982).

In contrast to the disabling accidents, the reverse trend was apparent

for non-disabling accidents. The frequency rate of non-disabling
accidents was lower for thin seam than for thicker seam mines. This can
be explained by the fact that thin seam coal accidents are likely to be
more serious when they occur since it is harder to get away from or to
correct a potential accident situation owing to the confined space. It was
found from analysis of sub categories of fall of roof that higher
proportions of accidents in thin seams occur during installation of timber
or other support, than in thicker seams. The difficulty of installing
roofbolts was identified and the protrusion of such support resulted in
obstructed travel ways, which could lead to head and back injuries
during machine movement (Clarke et aI., 1982).

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It was found that at mines with low accident rates the morale of the
people was good, the geological conditions in terms of strong roofs and
floors were good and that increased mechanization has led to fewer
injuries. The most common single injury on the thin seam mines was
that of a sprained back (Clarke et aI., 1982).

In the British collieries there was a steady decrease of the accident level
as miners became more safety conscious. The fatality rates have
decreased from 4 per 1000 men to 0.25 per 1000 men. The most
common injuries were from falls of roof and machinery and haulage
movement. The fall of roof rates for the thin seam in the U.K. mines are
much higher than for all other mines. This may be attributed to the lack
of mobility in the thin seam sections and the support tended to be of a
lighter construction to maximize available traveling and working space.
A relatively small proportion of accidents from machinery and haulage
movement occurs at the face. Most accidents in this category appear in
the load-out and out-bye areas. The rate in all haulage and transport
accidents is higher for thin seam mines than for thicker seams. In the
U.K. mines accidents of this nature contributes to over one third of all
serious accidents (Clarke et aI., 1982).

In the U.K. mines serious accidents from the use of hand tools in thin
seam areas are rare. Stumbling and falling accidents account for the
highest number of total accidents in a single category. This high rate is
reflected in the serious accident category and shows a higher rate for
thin seam than for thicker seam. The rate for serious accidents resulting
from slip or falls is much higher for thin seams than for all other mines
(Clarke et al., 1982).

In the former U.S.S.R. few statistics exist about their thin seam mining
operations. It is noted however that augering operations in the thin
seam mines have had no accidents. The conclusion can be drawn that

74
remote operation was much safer than any other mining method. No
certain conclusions can be made about any of the former U.S.S.R.
mining operations (Clarke et aI., 1982).

In the Republic of South African most of the thin seam coal mining was
done in Kwa-Zulu Natal. The accident rate in the thicker seam levels is
lower than in the thin seam levels, except where the No. 5 (not a thin
seam) seam has been worked in the old Transvaal province (now
Mpumalanga). Accidents from roof falls were more common in these
operations due to the weaker mudstone roofs. Haulage and transport
accident frequencies were also high due to the use of track equipment
and tubs in thin seam mines (Clarke et al., 1982).

In Colombia most of the coal production is from thin seam mines. The
collection of accident statistics is not reliable as there is no legal
obligation to report and record accidents. The reportedly high accident
rate in this country can be attributed to the lack of controls and
standards and not so much to thin seam conditions (Clarke et aI., 1982).

To conclude: the U.S.A. experience indicates that the accident

frequency rate per million man-hours of exposure in thin seams is
higher than in medium or thick seam mines. If the accident frequency
rate is calculated on the basis of accidents per million tons mined, the
thin seam rates are substantially higher than that for medium or thick
seams due to the lower productivity in thin seams. In the U.S.A. the
occurrence of hazards, involving mobile machinery in thin seams, are
partly due to the difficulty of working by means of bord and pillar
methods which involves frequent moving of large items of machinery in
confined spaces. The difficulty in supporting the roof is another
contributory factor. The U.K. and the former U.S.S.R. trials with remote
mining systems have indicated that men may be removed from the face
with the expected improvement in safety.

75
6.3. Health and Safety.
Hazards that result in physical injuries are easier to identify than those
that affect the health of workers. The reason for this is that the injury
normally occurs as a result of some violent event and the object that
cause the accident is directly identified. The detrimental effect on health
takes place over a period of time and until some loss or impairment of
body function has occurred, the employee may not be aware that the
process is taking place. The more obvious hazard to health is that
affecting the respiratory system, named pneumoconiosis. In thin seams
another health problem is beat diseases, which are caused by working
and traveling in unnatural positions. Beat diseases are more common in
ultra thin seams where miners work on their knees and elbows. These
diseases are described as sores, abscesses and swellings due to
constant beating of limbs against the roof and floor. Correctly fitting and
comfortable knee and elbow pads are important (Clarke et aI., 1982).
This condition is less likely to develop where remote control equipment
is used and the operator sits while working, but may be common
amongst the roof support crew and cable handlers.

Other environmentally related health problems are those associated

with working in close contact with water and oil, the danger to eyes from
particles picked up by high air velocities, noise and poor illumination
(Clarke et al., 1982).

Hazards to respiratory health in coal mining come mainly from inhalation

of respirable dust particles. In general the relationship between health
and dust apply to all seam conditions. The problem may be more acute
in thin seams owing to higher velocities of air needed to supply the right
velocities to the coalface. In the U.S.A. some thin seam mines required
dilution of methane and the only way to get enough volume for the
dilution was to increase the velocity. High velocities may produce a

76
 counter effect by causing dust pickup. Velocities above 2 mls cause
appreciable pickup of dry dust but, when the dust is wet, velocities of
above 4 mls can be tolerated. Particle size also affects the pickup of
dust. Items of equipment in roadways can cause restrictions in cross
sectional areas and result in funneling of air with a resultant increase
velocity at the restricted point. In the vicinity of any cutting machine at
the coalface, the area is reduced causing funneling of the air with an
increase in velocity at that point. It is particularly important in thin seam
coal mining that adequate dust suppression equipment be used (Clarke
eta/.,1982).

In thick and medium seam collieries, water on the floor is merely a

problem that should be dealt with. In thin seams however the problem is
more severe when miners become sodden from crawling and sitting on
wet "floors. The use of hydraulic fluids in equipment and machinery
causes skin diseases such as dermatitis. Spillage must be kept to a
minimum and protective gloves must be worn at all times. Complaints
such as colds, influenza and rheumatism may develop where the
ventilating air is cold and the wet miners move in and out of this cold air
(Clarke et a/., 1982).

The amount of noise in thin seam working conditions is much more

pronounced than in larger working spaces. It is therefore imperative that all
workers wear hearing protection at all times. The advantages of remote
control operations are obvious as in the case of noise as the operator is
physically removed from the source of this noise (Clarke et a/. , 1982).

6.4. Production rate and costs.

In thin seam mining a greater area of ground has to be mined in order to
extract an equivalent tonnage to that from thicker seams. Many of the
tasks that have to be performed in underground mines are related to
linear advance and so for a given output they must be carried out more

77
frequently in thin seam mining. Extensions of rail track, conveyor belts,
water- and power lines can reduce the productivity in thin seam
sections. Other tasks such as sweeping and stone dusting needs to be
done and are directly related to area extracted and not tonnage mined.
These factors reduce productivity in thin seam mining. In the late 1960s
many mines still operated at 10 tons per manshift. This production
output has increased with the introduction of longwall mining methods
and bigger and more powerful continuous miners. The greatest risk to
the production rate is the lack of availability of mining equipment,
adverse geological conditions, high equipment maintenance and
downtime on the transport systems (Clarke et aI., 1982).

The direct result of a low productivity is the escalation of cost. Although

the fixed costs cannot be changed. its component in the Rand I ton cost
of the RO.M. tons, will increase. With the high output this component
becomes less pronounced in the Rand I ton costs of the RO.M. tons
e.g. if the fixed component equal R 200 000.00 per month and the
section produces 20,000 tons per month, the RO.M. fixed cost is
R 10.00 I ton. If the section only produces 10,000 tons for that month,
the RO.M. fixed costs will be R 20.00 I ton. Likewise the variable cost
will be influenced by additional maintenance and repair costs during
adverse mining conditions. It is common for collieries to have a high
fixed cost and relatively small proportion of variable cost. This feature of
a mine makes it imperative that output targets are achieved. Nearly all
the profits come from marginal tonnage i.e. tonnage mined over and
above the base tonnage.

Another risk factor that seriously affects the cost of thin seam mining is
the yield. By either cutting the floor or the roof the yield from the thin
seam sections would be reduced which in turn would increase the costs.
Therefore it is imperative that mining horizons being maintained to
produce is much coal as possible and exclude contaminants.

78
 CHAPTER 7: CURRENT THIN SEAM MINING TRIAL.

7.1. Continuous Miner and Battery Haulers.

In 2002 the German company Maschinen- und Bohrgerate Fabrik GmbH
designed a thin seam continuous miner that is capable of cutting as low as
1.0m. It is called the Wirth Paurat H4.30. (For specifications see Annexure 3).
The main purpose of this design was to directly compete with the American
company, Joy Mining Machinery (a subsidiary of Joy Global Inc. Company),
which has a huge market share in the U.S.A coal mining industry and in the
RS.A and who also specializes in thin seam mining equipment (pers.
comm.). T.C.S.A management heard about the new development and
enquired about the possibility to test this machine at Dorstfontein Mine and
compare it to the current Joy 12HM15 on the mine. It was agreed to, with the
arrangement that Dorstfontein uses and tests the machine for 1 year at a fixed
rent after which T.C.S.A has the option to buy the machine at a reduced
price. The Wirth arrived at the mine in middle December 2002 and moved into
a section where the seam height is 1.6m. For the coal haulage there are 2
Stamler BH10 thin seam battery haulers (For specifications see Annexure 4).

The Wirth is equipped with a DebbexlKennametal double rotating drum,

which has been designed to be able to cut thin stone bands. The
configuration of the cutterhead is such that a fair amount of the large coal
fraction is produced and the fine fractions kept to a minimum.

Initially there were problems with the power supply and software of the
Wirth as this machine was built and assembled in Germany and needed to
be adapted for South African conditions. A few minor design errors also
needed to be corrected on mine to suit our specific conditions. Once the
Wirth was in operations it was clear that this machine is well constructed
and built and should easily cut in-seam partings and even be able to pull
down the seam-split parting in areas where roof brushing is necessary.
Presently the parting is being blasted down by drilling holes into the upper
coal seam as there exist the potential to damage the machine. Further
problems needed to be sorted out during the following few months in order
to achieve full production. During March 2003 the standing time became
less and availability started to increase. The increased availability has led
to another problem regarding the availability of the Stamler BH 10 thin
seam battery haulers. The Wirth machine cuts too fast for the 2 battery
haulers and has to wait before it can discharge more coal from its bin. It
became apparent that there is a need for another thin seam battery hauler.

The installation of roofbolts to support the parting is quick and no delay

times have been experienced during their installation.

The Wirth has a cutting range between 1,0 and 2.8 m but will spent most of
the trial time cutting between 1.5 and 1.6m. The maximum allowed cutting
depth is 12m, for safety reasons, after which the parting needs to be
supported before the machine can cut that heading again. Roof brushing is
currently been done only in the combined travel and belt road, while full
support of the parting is done in al\ the other roads. The planned production
rate is 1250 tons per day for the first year after which production will be
increased to 1500 tons per day for six years and then again reduced to 1250
tons per day for the last three years. This gives an average production rate of
1400 tons per day for ten years. The lower production rate in the first year is to
allow time for all the problems with the new machine to be solved while the
lower production in the last three years is to allow lower productivity in the very
low seam areas.

The current labour complement is as follows:

1 x Miner
1 x Continuous miner operator
1 x Continuous miner assistant
- 2 x Hauler drivers
1 x Feeder-breaker overseer

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 1 x Roofbolter operator
1 x Roofbolter assistant
- 4 x General labourers
A total of 12 persons per shift.

7.2. Ventilation
The primary consideration when determining the ventilation requirements for
thin seam mining is the provision of healthy, safe and comfortable working
environment. Sufficient fresh air must be supplied to the workings to keep the
concentration of methane in the general body within the legal limits which
prescribes an concentration in the air below 1,4% per volume, reduce dust
concentration to at least 1,0 mg/m 3 and maintain air velocities of not less than
1,Om/s along the last through road in the section. As shown in Chapter 6
equipment in roadways can cause dust pick-up and chOking of the airflow to
the face (Clarke et aI., 1982).

Methane emission tests are done on a regular basis by taking core samples
from a production face at the mine. Some of the results are tabled below.

Gas Content (mj/ton) Emission rate (liters/tons/min) I

0.95 34.3 I

Normally a thin seam does not emit large quantities of methane (small volume
of coal) but caution should be taken near dykes and where dolerite sills over1ie
coal seams to form a cap that prevent degassing of the strata during
secondary coalification. This is not the case at Dorstfontein Mine and methane
gas should not be a risk in the thin seam areas. The maximum allowable
concentration of methane in the general body of the air in any place where
people are required to work or travel is 1,4% by volume. If a limit of 0,1% is
used to determine the dilution volume of air, then a safe volume of air of at

81
least 15m 3/s will be required to ensure that the methane content of the return
air volume does not exceed this 0,1%.

Calculation (Van Zyl, 2001, pers. comm.):

• m3/ton/min = 34.3 liters I ton I min + 1000 => 0.0343 m3 1ton I min
3
• The CM cuts 22 tons I min => 22 x 0.0343 = 0.7546 m I min of gas
released during cutting.
• To get to the ventilation needed:
0.7546 m3 1 min + 60 =0.01257667 m3 1sec gas released.
• The dilution needed is 0.1%:
3
0.01257667 m /sec+ 0.1% =12.577 m3/sec
To be safe, use 15 m3/sec

The air volume necessary to ensure healthy and safe working conditions will
be more than that required to dilute the methane. The ventilating air will be
distributed to at least the last two through roads from the faces at a minimum
velocity of 1,0 m/s. This will require a quantity of air calculated as follows:
Average seam height: 1,3m
Bord width: 6,8m
Section air quantity = last through road area x velocity
= (6,8 x 1,3) m2 x 1,Om/s
= 8.8 m3/s

By allowing 40% for leakage (Van Zyl, 2001, pers. comm.) and adding 15
m3/sec for dilution, the volume must be increased to at least 27 m3/s. A
conservative figure of 30m 3/s for the Wirth-section will be sufficient which is
not much less than the 35 m3/s currently supplied to the sections on the mine.

The current practice of erecting brick stoppings between pillars to separate the
intake and return air roadways will be maintained. A jet fan capable of
3
handling an air volume of 4m /s will be used to positively ventilate the

82
 advancing face in the Wirth-section. Directional water sprays in association
with a dust scrubber are currently been used on the Wirth. So far it has
effectively controlled the dust liberated during cutting operations. The dust
scrubber installed on the Wirth currently handles an air volume of 7m3/s.

In order to achieve a last through road velocity of 1.0 m/s the total amount of
air to the section should not be less than 30 m3/s. The current ventilation fan
on the mine is capable of supplying this additional air to an extra underground
section. To channel the air to the new working area, some additional
aircrossings will have to be constructed at a current cost of R 15,000 each,
which have been catered for in the financial evaluation.

7.3. Rock mechanics.

7.3.1. Split-seam parting tests and results.
Detailed evaluations of the seam-split parting were done by Mike Spengler,
the practicing rock engineer on the mine. These tests involved impact splitter
as well as compressive strength tests. A detailed report is attached as
Annexure 6. From these tests it was clear that the parting is strong and
competent enough to form a safe beam to undermine. Due to safety reasons
and to uphold the safety record of the mine, it was decided to construct a
double safe beam by suspending the parting and upper coal from the proper
roof using 1.5m full column resin bolts as well as clamping the layers together
to for a strong beam (Spengler, 2002).

7.3.2. Support pattern and cutting sequence.

For the support pattern and cutting sequence that will be introduced in the
thin seam areas, see Fig. 7.1 and 7.2. The generally accepted safety factor
for coal mines is 1.6 where the probability of pillar failure is only 0.998468
(Van der Merwe and Madden, 2002). For shallow to medium depth mines
with a very competent roof is general practice to design the bord widths to
seven meters while six meters is used in mines with poor roof conditions.
With this knowledge and working to a safety factor of 1.6, the pillar widths

83
 can be calculated using Salamon's Formula (Van der Merwe and Madden,
2002, p. 51). At Dorstfontein the centers (from the middle of the pillar to the
middle of the bord) is 13.5m at a safety factor of 1.6.

7.4. Advantages of thin seam coal mining.

It is human nature to follow the easiest way to reach a goal. So why would
companies pursue thin seam coal mining and why would Dorstfontein specifically
pursue the thin seam resource? There are many reasons and some of it has
been dealt with in other chapters of this treatise. The current mining trial at
Dorstfontein Mine has confirmed what has been suspected for a very long time.
The following reasons make it worth pursuing the thin seam coal beneath the
seam split parting:
a.) During the mmmg trial with the Wirth machine, the yields increased
significantly by 8 percentage pOints from about 72% to about 80% within a
matter of a few days of mining below the parting. In this, one of the most
important objectives of this exercise were met namely to improve the yield
by undermining the seam-split parting.
b.) There is less standing time due to discharge shoot- and crusher
blockages caused by the seam-split parting breaking up in huge lumps
and fouling up the coal chain to the plant.
c.) One big advantage is the saving in belt replacements and maintenance.
When the seam-split parting gets dumped on to the main belt gOing out of
the mine, holes are punctured into the belt due to the weight and shape of
the stone. This has been reduced, as there is less stone coming from this
section.
d.) In order to increase yields and prevent damage to the belts the section
crew picked some of the stone by hand to be stowed underground.
Fortunately no injuries occurred during the handling of the stone, but a
chance existed that an accident could have occurred. This kind of injury is
now less likely as the current handling of stone underground, has been
reduced.

84
e.) The biggest and most important advantage is the extension in the life of
the mine and the longer utilization of existing facilities. Further more there
is the extraction of the whole No.2 Seam reserve and the additional
revenue coming from this thin seam resource.

85