The document discusses the challenges of extracting coal from underground mines that have been developed with pillars, by using opencast mining methods. It notes that as opencast mines deplete virgin coal seams, developed underground pillars will be an important future source of coal production. Extracting coal from these areas is challenging due to risks like coal dust explosions, pot holing, and mine fires. The document outlines safety guidelines from DGMS for working in areas with thin rock partings above underground galleries and for blasting near underground workings impacted by fires. It also describes the processes used to plan extraction zones and safely compact underground galleries during conversion to an opencast mine.

1. 1
Tikeshwar Mahto,
Dy. Dirctor Mines Safety,
Bilaspur Region
tikeshwarmahto@yahoo.co.in
SAFE EXTRACTION OF DEVELOPED PILLARS BY OPENCAST METHOD –
A CHALLENGE FOR MINING ENGINEERS : A Case Study
ABSTRACT
Dependency of our energy requirement on coal in future will still continue till the
technology advancement in the field of renewable energy. Presently 60% of the
total energy demand is fulfilled by coal. The coal production of country in the
financial year 2012-13 is around 557 Mt. The share of opencast mines is more than
70%. Opencast mines are shrinking day by day due to exhaustion of virgin coal.
Extraction of coal by Underground mining is very uneconomical. In future there will
not be any virgin coal seam for opencast mining and only alternative for coal
production will be by open casting of developed pillars of underground mines. There
are nearly 3 to 3.5 BT of coal reserves in standing pillars in the country. In SCCL
there are 15 open opencast mines and mostly working on developed pillars of old
underground mines. Upcoming opencast projects are being planned on old
underground mines. And future of mining engineers will be very- very challenging.
In this paper the author is expressing his experience about the challenge to extract
the coal from the underground developed pillars.
Introduction
The author has worked in RG OCP-I, a big opencast mine (5Mt) of SCCL, running on
old developed pillars and goved out areas of GDK. NO.-9 Incline & GDK.NO.- 10
Incline Mines. The mine is having a Dragline, Rope Shovels & 12 Cum Hydraulic
Shovels (Diesel version). Dip side of the underground mines are separated from rise
side workings by constructing dams and underground mines are running still on dip
side of the property by making alternative approaches. Standing pillars & goaved
out areas in Rise side of the old underground mines are being worked by opencast
method. Working in this mine is challengeable as far as ground control & fire are
concerned.
Extraction of Developed Pillars by Opencast Mining
Extraction of U/G developed pillars by opencast method is very challengeable for
mining engineers. Blasting operation on developed pillars is very critical activity of
the mining operation. There are chances of Premature detonation of explosives in
fiery holes, if proper precautions are not observed. Such type of accidents have
already occurred in opencast mines operating on underground developed pillars.
There is history of Coal dust explosion due to blown through shots. Pot holing is also
a notorious name in underground converted opencast mines. Earlier in a mine
accident, one Assistant manager fell in a pot hole having active fire and couldn’t be
recovered. Recently in an opencast mine a Dumper operator jumped from the
dumper after seeing heavy inrush of smoke from a pot hole in front of dumper and
fell into the pot hole and died instantly.

2. 2
DGMS Circulars issued time to time regarding extraction of developed
pillars
1. Precaution against danger of coal dust explosion while extracting pillars by
opencast method (Cir. Tech. 4/1980)-Attention is invited to DGMS (Tech)
Circular No. 11/1979 in which it was stipulated that LOX shall not be used for
blasting in overburden within 15m of the underground workings in the coal seams
immediately below or in the vicinity. It was also suggested that:-
 No shot hole shall be drilled in O/B above underground galleries.
 A parting of at least 3m between the bottom of a shot hole and the coal seam shall
be left intact.
The above precautions have to be observed not only with LOX but
With all other types of explosives used in opencast mines.
After a coal dust explosion in an opencast mine, the previous guidelines were
elaborated to prevent a recurrence of the accident. The Precautions to be taken in
this connection are listed below-
 Survey, Cleaning and dusting: Where the U/G workings are accessible, the same
shall be surveyed and cleaned of all coal dust and thickly stone dusted before
commencement of extraction of pillars.
 Withdrawal : All persons from U/G in the same workings seam or any other seam or
section connected therewith shall be withdrawn before commencement of blasting
operations in the quarry and the work persons shall not be permitted into the said
U/G workings unless and until the same have been inspected by a competent
person
OR
The U/G workings to be quarried shall be isolated by explosion proof stoppings or by
any other approved manner from any active working area either in the same seam
or different seam or section as the case may be, so as to prevent transference of
danger to the said working areas.
 Location of holes: The spacing of holes in the bench lying immediately above the
coal seam (referred to hereinafter as last OB bench) shall be so adjusted that the
holes do not lie immediately above the galleries as far as possible in order to ensure
that the blast holes do not directly fire into the U/G workings.
 Safe parting: The depth of the hole in the last OB bench shall be such as to leave at
least 3.0 m thickness of OB above the coal seam, and to ensure compliance with
this requirement a pilot hole be put for each round of blasting to determine the total
thickness of OB over the coal seam.
NOTE:- This condition has been modified in subsequent DGMS
Circular, which is as follows?
 No person or machinery shall be deployed or permitted to be deployed in any
portion of the quarry lying over U/G galleries, free from water, where the thickness
of parting is less than 6 m in coal or 4 m in O/B.
 To comply this conditions parting of at least 4 m thick immediately above the
developed pillars shall be blasted at once including thickness of coal seam to

3. 3
prevent any sinking of HEMM and persons into any U/G galleries during extraction of
coal.
 Filling sand in holes: Where there is any doubt and particularly where there is any
cracks and crevices, the bottom 2m length of the hole shall be filled with sand.
 Delay detonators not to be used: Unless otherwise permitted by DGMS, no delay
detonators shall be used in coal and the manner of extraction of pillars shall be by
drilling & blasting holes in coal pillars only from top downwards.
 Workings developed in more than one section : Where more than one section of the
seam had been developed on pillars, the shot holes shall not be drilled 3m of a
lower section, and care shall be taken that, as far as possible the blast hole do not
directly fire into any U/G gallery. To ensure compliance with requirement, a pilot
hole shall be put for each round of blasting.
 Use of water ampoules/moist sand: All holes in the last OB bench and/or in coal
shall be charged with water ampoules or with moist sand of at least 0.6m in length
at the bottom of the hole.
 Shelter: No person including shot firer take shelter within 100m of the quarry
openings, and such shelter shall be of an approved design.
 Administrative control: The opencast working over U/G part of working shall be
under the administrative and technical direction and control of the Manager and
Agent.
2. Blasting in Fire areas (Cir.Tech.2/1985 & 2/1990): A number of
fires are known to be active in different Coalfields. Any attempt to win coal from
these areas involving blasting is fraught with danger. In a major accident, 6 persons
were killed when a NG- based explosives was being used in an opencast coal mine
where fire existed.
Some trial were carried out by R&D wing of DGMS in collaboration with CMPDIL and
CMRS in extraction of coal from fiery opencast mine and recommended the following
precautionary measures:-
 No explosives other than slurry and emulsion explosives shall be used.
Blasting shall be done with detonating fuse down the hole.
 Temperature inside the blast holes shall be measured (before filling with water)
and, if the temperature exceeds 80
0
c, in hole, such hole shall not be charged.
Records of measurements of temp. in each hole shall be maintained in a bound
paged book.
 All blast holes shall be kept filled with water. When any hole is traversed by cracks
or fissures, such hole shall not be charged unless it is lined with asbestos pipe and
the hole filled with water. In addition, bentonite should be used for sealing any
cracks at the bottom of the holes.
 Detonating fuse shall not be laid on hot ground without taking suitable precautions,
which will prevent it from coming in contact with hot strata.
 The charging and firing of the holes in any one round shall be completed
expeditiously and in any case within 2 hours.
 Blasting operations shall be carried out under the direct supervision of an Assistant
manager.

4. 4
It is however, clarified that permission/relaxation under different regulations, which
may be applicable (e.g. using more than one type of explosives etc.) shall invariably
be obtained before carrying out blasting operations.
3. Firing of shots in fire areas/in vicinity of hot strata in opencast Coal mines
[DGMS (Tech) Circular 4/2006]:-
Recently, in a mechanized opencast coal mine, where extraction of developed pillars
by deep hole blasting was being carried out, one of the shot hole left charged,
prematurely detonated after a lapse of two and half hours. Fortunately no person
was involved as the holes were unstemmed and there was no one in the vicinity.
The following additional precautionary measures shall be taken over and above the
measures stipulated vide DGMS (Tech.) circular 2/1985.
 The blasting officer shall ensure accurate measurement of temperature at bottom of
the shot holes drilled in coal benches and in O/B benches immediately above the
coal seam and other fiery areas to determine whether fire exists. The measurement
shall be recorded in a bound paged book kept for the purpose. For this purpose the
temperature shall be measured initially after completion of the hole and thereafter
at least once every shift. No hole shall be charged, if the temp. in the hole exceeds
800
C.
 As a precaution against presence of pocket fires in coal benches in developed
seams, O/B benches immediately above the coal seams and other fiery areas in the
mine, the explosives charged shall be fired by detonator attached to the detonating
cord at the surface and not within the shot hole.
 All explosives, cast boosters, detonators, detonating cord and shock tubes shall be
subjected to proper testing in an approved laboratory in respect of temperature
sensitivity and impact sensitivity for safe handling in mines. A certification to that
effect shall be supplied for each batch.
 Sleeping of holes shall not be permitted in coal benches, where fire or Spontaneous
heating has been detected and in O/B benches lying immediately above such seam
and at all places where there is likelihood of fire or Sp. Heating.
 No PETN/TNT based cast booster shall be used for initiating non- cap sensitive
slurry/emulsion explosives in coal benches and O/B benches of a fiery coal seam.
Processes before starting extraction of developed pillars by
Opencast methods are as follows:
The U/G workings to be quarried shall be isolated by explosion proof stoppings or by
any other approved manner from any active working area either in the same seam
or different seam or section as the case may be, so as to prevent transference of
danger to the said workings area.
Before intended to close the U/G mine for conversion to O/C, a detailed off set
survey has to be conducted by using latest survey equipments like Total Station etc.
and the position of workings including the disturbances and falls should be clearly
demarcated on the plan.. The U/G mine Manager should see that the plan prepared
for handing over to Opencast mine manager is flawless, because once the U/G mine
is abandoned, the O/C operation becomes blind folded and only guidelines remains
with the O/C management is U/G plan submitted by the surveyor of U/G Mine. It
should clearly picturise the each and every detail of U/G workings.
Cleaning of all coal dust and thick stone dusting before commencement of
extraction of pillars.

5. 5
Retaining of key personnel of U/G mine, like Surveyor, Overmen and Officers for
safe and effective operation of O/C mine.
After completion of all legal and statutory formalities, the mine is developed as per
the permission conditions of DGMS. For safe and systematic excavation, the mine is
divided into four zones viz.
A. SAFE ZONE.
B. CRITICAL ZONE
C. DANGER ZONE AND;
D. COMPACTED ZONE
(A) SAFE ZONE: It is the zone of safety, where the parting is over U/G galleries is more
than 15m. In this zone all activities can be carried out and the zone is to be
demarcated with `White` flags.
(B) CRITICAL ZONE: It is the zone, where proper precautions are required for
excavation. In this zone, the parting of working O/B benches over U/G galleries is
more than 4m and less than 15m. Whenever, the plan parting reaches 15m to u/g
galleries, further reduction shall not be done unless it is proved physically. After
proving the physical parting, further parting is reduced to 4m hard O/B. In this zone
the excavation is done by Back hoe shovel in level loading. This zone is demarcated
with `Yellow` flags.
(C) DANGER ZONE: Danger zone means, the area where the parting over U/G galleries
is 4m hard O/B or less. No work shall be done in this zone except dozing and drilling
for compaction. The dozing and drilling shall be done under proper supervision.
Danger zone is to be demarcated with `Red` flags.
(D) COMPACTED ZONE: When danger zone is converted to safe zone by Compacting the
U/G galleries by drilling and blasting (4m O/B and coal seam combindely), it is
termed as `Compacted` zone. This zone is permitted for normal extraction of
coal/OB, as it is safe. It is demarcated with White flags.
Note: As per DGMS guideline, the extraction of O/B in Critical zone should
be done upto 4m parting over galleries, but 4m hard O/B parting is not safe
for running HEMM and formation of pot- hole can’t be avoided. Hence for
extra precaution, Critical zone is assumed between 6-15m. When the
working in critical zone reaches to 6m, it is treated as danger zone.

6. 6
O/B Parting over the Galleries in different zones
Fig: 1
Working in different zones:
I. Whenever the area reaches to critical zone as per plan parting observed by the
Surveyor, test holes shall be drilled at demarcated places to prove the physical
parting. The critical area is demarcated with `Yellow` flags.
II. Based on the proved parting, O/B benches shall be lowered upto danger zone.
III. Whenever the area reaches to danger zone, the area will be leveled for drilling
under proper supervision. Then the surveyor will mark the position of U/G galleries
and drill hole pattern on the benches with stone dust as per the approved plan. The
surveyor will display the play cards at the junctions mentioning the place and plan
parting on it.
IV. The Surveyor will hand over the notice of the galleries and parting with sketch to
the Overman, Under Manager, Blasting In-charge, General shift In-charge and to
the Manager of the mine, before operating in Critical and danger zone.
V. General shift In-charge will give the necessary instruction in writing to the
concerned Shift persons regarding drilling and extraction in critical and danger zone.
VI. Test holes shall be drilled to ascertain the parting before commencement of actual
drilling operation.
6m
15m 12m
Danger
Zone
Critical
Zone
Safe
Zone
18m
O/B
Coal Seam with
Developed galleries
Compacted
Zone

7. 7
VII. Based on the above test hole report, the termination of holes over the galleries will
be ascertained. In O/B, the holes above the galleries shall be terminated 1.5- 2m
before touching the galleries and in coal 2-3m for providing proper confinement of
explosives column around the holes and to avoid blown through shots in the
galleries.
VIII. The drilling on pillars and galleries shall be done as per the pattern shown in the
sketch provided by the Surveyor and under the supervision of an Overman.
IX. The Overman and Under Manager In-charge will record the proved partings and
pattern of drilling with depths and will be kept for the purpose.
Compaction of Galleries a critical activity of the U/G converted Open cast
mine:
When the operation of the mine falls in the danger zone (i.e. parting over galleries
is less than 6.0m), it needs careful progress to expose the developed coal seam. As
per DGMS guideline, at least 4m thick O/B parting (here 6m) immediately above the
developed galleries shall be blasted at once including thickness of coal seam to
prevent any sinking of HEMM and persons in to the U/G galleries during extraction
of coal. Here, O/B and coal are blasted simultaneously by drilling holes from O/B to
floor of the galleries in coal to compact the galleries is called combined blasting.
(A)Drilling pattern for combined blasting when the galleries are
developed in single section:
F
R
E
E
F
A
C
E
A A`

8. 8
Section along A –A` showing depth of holes on pillars & galleries
(B) Drilling pattern for combined blasting when the galleries are
developed in two sections with superimposed galleries:
F
R
E
E
F
A
C
E
A A`
Coal Seam with
Developed galleries
O/B

9. 9
Section along A –A` showing depth of holes on pillars & galleries
Fig: 2
(C) Drilling pattern for combined blasting when the galleries are developed in
two sections and parting between two sections is more than 6 mtrs:
If the parting between two sections is more than 6 mtrs, the combined drilling &
blasting should not be done in the fashion as shown in the Fig.2. The author has
experienced that, if the combined blasting is done in the fashion as shown in Fig.2,
there is coal loss of around 10-20% in the form of contamination. The economical
aspect is also taken into account in addition to safety factor. DGMS has
permitted to maintain minimum parting of 6m in coal or 4m in O/B.
Therefore, combined blasting can be done separately for both the sections, when
the parting between the two sections is nowhere less than 6 mtrs. First combined
blasting is done in 6m (O/B) and 3m Coal (i.e upto the bottom of the top section
gallery). After exposure of Coal, the above procedure is repeated separately for
gallery compaction in bottom section. The exposed coal is leveled with dozer and
demarcation of bottom section galleries is made with stone dust. Drill is engaged
under proper supervision to test the parting of bottom section gallery. Then
pattern of drill holes are marked for drilling & blasting. After blasting in coal, again
it is compacted with dozer before lifting the coal.
O/B
Coal Seam with
Developed galleries

10. 10
The drilling & blasting pattern in both the sections separately are shown
in figure below.
Section along A –A` showing depth of holes for compacting only top
section galleries
Section along A –A` showing depth of holes for compacting bottom
section galleries in coal after exposure.
O/B
Exposed Coal
Fig.4
O/B
Parting between
two sections is
more than 6mtrs
Fig.3

11. 11
Another disadvantage of combined blasting at a time of both sections is fire. When
full depth of coal is blasted combindely and left for few days, the fire spreads more
rapidly throughout the depth of coal due to more area of contact with air and some
times it becomes very difficult to control the fire.
(D) Drilling pattern for combined blasting when the galleries are developed in
two sections and both the sections are not superimposed (i.e. staggered ):
When the galleries are staggered and parting between two sections is less than 6m,
then drilling & blasting activities become very critical. The author has applied many
trial and error techniques and finally established a system, which is being continued
in the mine. Both the galleries are marked with different colours. Top section gallery
with white stone dust and Bottom section with black coal dust, so that we can easily
distinguish both the sections. Then holes marking are done with reference to the top
section gallery. Only care is taken that the drill holes, which are close to the bottom
section gallery, are terminated 3m before touching the gallery and remaining holes
are drilled upto floor of the bottom section gallery as shown below..
Fig.5
Section along A –A` showing depth of holes for compacting both
galleries when parting is less than 6m.
O/B
Parting between two sections is
Less than 6mtrs with staggered
gallery

12. 12
(E) Drilling pattern for combined blasting when the galleries are developed in
two sections with parting more than 6m, in the intention to reduce the
number of holes for making charging and blasting comfortable on the
same day:
Fig.6
Section along A –A` showing depth of holes on pillars & galleries for
compacting top section galleries. Fig:7
O/B
F
R
E
E
F
A
C
E
A A`
B`
Coal Seam with
Developed galleries
B

13. 13
Section along B –B` shown in fig:6 in Strike direction, showing depth
of holes on pillars & galleries
Fig:8
When the O/B bench immediate to the galleries is tested and declared for danger
zone, a stringent care should be taken till the compaction of galleries. A First class
Certificate holder should be the In-charge of the compaction of galleries. He will
monitor everything starting from drilling to compaction of the galleries.
Precautions while drilling over galleries:
 Code of Practice shall be framed and implemented before starting the extraction
in the mine and following will be the salient features:
a) While marching the drill, it should not be marched over the U/G galleries.
b) Drill should not be marched over the gallery junctions.
c) Drilling should be carried out by placing the drill over the pillar.
d) Whenever any hole is inadvertently punctured into the gallery a fresh hole shall
be drilled 1.0 m adjacent to the hole.
 After leveling the danger area carefully by an experienced Dozer operator, the
position of the junctions and galleries edges shall be marked with play cards and
stone dust respectively by the Surveyor. Play cards will show the Plan parting.
O/B
1.5- 2,0m
Above the
gallery
D
I
P

14. 14
 The In-charge for galleries compaction will arrange drill under personal supervision
of an Overman to prove physically the parting over the galleries. After proving
physical parting, the Surveyor will circulate the report to all officers and supervisors
and the same will be recorded for compliance of the statute. As per the physical
parting report, drilling pattern shall be decided.
 If the galleries are developed in single lift and the depth of hole on pillar is less than
10m, a drill of 150 mm diameter is adequate to compact the galleries. But, if the
galleries are developed in double lifts (Top & Bottom), the depth of the hole on pillar
will be more than 20m. For this, small diameter (150mm) drill will not be capable to
compact the galleries perfectly. For this purpose, larger drill of diameter 250mm will
be required.
 If 250mm dia. Drill is used for drilling over the gallery, as shown in Fig. 1,2 &3,
single row is sufficient to collapse the gallery. But, in case of drill of 150mm dia, two
rows will be required.
 Holes over the galleries shall be terminated 1.5m – 2.0 m before touching the
gallery and this will be decided on the basis of test holes report, drilled at junctions
and galleries.
 A survey person shall be deployed, while drilling on galleries and pillars to guide the
drill operator and record the depth of the holes as per the hand sketch prepared by
the Surveyor.
 Holes on the pillars shall be drilled upto floor of the gallery (in case of two sections,
the holes should touch the floor of the bottom section gallery as shown in Fig.2 &3).
 Pattern of holes on pillars:
 For 10 m hole depth, the burden & spacing pattern shall be 5m X 6m for 150mm
diameter drill and 6m X 7m for 250mm diameter drill.
 For 10m – 15m hole depth, the pattern of burden & spacing shall be 6m X 8m for
250mm diameter drill.
4m
4m
2mFor 250mm drill For 150mm drill

15. 15
 For more than 15m depth of the hole, the burden & spacing pattern shall be 7m X
9m for 250mm diameter drill.
 The distance between first line of holes and edge of the gallery should be 2.5 to
3.0m, as shown below;
Charging & Blasting operation:
 After completion of drilling, Blasting In-charge shall inspect the area and shall make
estimation of explosives required on the basis of depth of holes. As far as possible,
the drilled holes shall not be left for long time to avoid catching fire. As per DGMS
circular mentioned above, no slurry or emulsion explosives shall be used in fiery
holes and we can’t avoid fire in holes drilled for combined blasting purpose. Hence,
only LDC explosives with detonating Cord shall be used for blasting to compact the
galleries.
 Temperature of the holes shall be measured with Infrared based thermometer and if
it exceeds 80
0
C, the charging shall be stopped. Charging and blasting in fiery holes
shall be done as per the DGMS circular Tech.2/1985 & 2/1990 mentioned above.
D
I
P
2.5- 3.0 m
F R E E F A C E

16. 16
 Charging of holes on pillars :
 If the galleries are developed in single lift in Top section of the Seam as shown in
Fig. 1, the depth of holes on pillars shall be in range of 9m to 13m, in which O/B
parting will be 6m to 10m and 3m coal (upto gallery height). Charge columns in O/B
and Coal shall be separated by a Deck of 2-3 m height.
Charging pattern of 150mm diameter hole
Explosives charge in Coal = 31.25 Kgs.(four Cartridges, each of 6.25
Kgs)
Explosives charge in OB = 62.50 to 93.75 Kgs.
Total charge in a hole = 93.75 to 125 Kgs
 If the galleries are developed in single lift in Bottom or Middle section of the Seam
and Coal parting above the galleries is more than 6m, then combined Blasting is not
required. Coal will be exposed in a normal way and after exposure of coal seam;
total thickness of coal will be blasted at a time taking all necessary precautions
narrated above. Only extra precaution to be taken is that, the advance test holes at
junctions shall be drilled in OB benches to know the coal parting above the galleries.
 If the galleries are developed in double lifts or sections as shown in Fig. 2 & 3, the
depth of holes on pillars shall vary as per the thickness of coal seam. Let us assume
that, the thickness of coal seam is 16m, then depth of holes on pillars will be in the
range of 22 to 26m, because OB parting will increase along Dip direction.
Coal (3m)
OB (6-10m)
Charge column in Coal (1.5m)
Deck column (2.5 - 3m)
Charge column in OB (2.- 5m)
Stemming in OB (3- 3.5m)

17. 17
Charging pattern of 250mm diameter hole
Explosives charge in Coal
In Ist Deck = 250 Kgs. (LDC each of 6.25 Kgs)
In IInd Deck = 250 Kgs
Explosives charge in OB = 100 to 250 Kgs.
Total charge in a hole = 600 to 750Kgs.
If the total number of holes on pillars is 32 (16 on rise side and 16 on dip side), as
shown in Fig.3, the amount of explosives required is
= 600 X16 Kgs + 750 X 16 Kgs
=9600 Kgs + 12000 Kgs
= 21600 Kgs
 Charging of holes on Galleries:
Parting above gallery in OB varies between 6- 10 m. Hence, depth of the holes
above the gallery in OB will be 4- 8m, term inating the hole 2m before puncturing
into the gallery. The amount of explosives required will be 62.5 Kgs to 125 Kgs.
If, the total number of holes above the galleries in OB is around 23(10 in dip side
and 13 in rise side), as shown in Fig.3. Then the total amount of explosives required
will be = 62.5X13 Kgs + 125 X 10 Kgs
= 812.5 + 1250 Kgs
= 2062.5 Kgs.
C
O (16m)
A
L
B/S
T/S
OB
(6 to 10
Charge column in Coal (5m)
Decking in Coal (4m)
Charge column in Coal (5m)
Decking in Coal & OB (3m)
Stemming column in OB( 3 - 4m)
Charge column in OB (2- 5m)

18. 18
Hence, total amount of explosives for on one round of blasting is
= 21600 +2062.5 =23662.5Kgs.
So, in one round of blasting 23-24 tonns of explosives is required.
Compaction of gallery after blasting:
Immediately after blasting, a dozer (minimum of 355 H.P.) with experience operator
shall be engaged under proper supervision for leveling & compaction of the blasted
galleries. After proper compaction, the area will be marked with `White` flags to
treat as safe zone for extraction.
Precautions while extracting in compacted zone:
After proper compaction of the area, again gallery and junction shall be marked with
stone dust and with`White` flags. Also a limit line shall be marked for the
excavation. Excavation will be done under personal supervision of an Overman. Coal
should not be left exposed for long time. After exposure of coal, it should be
dispatched immediately; otherwise a serious risk of fire will be created.
Precaution against fire: Spontaneous heating & Fire is a common phenomena in the
Opencast Mine excavating the developed pillars. If the fire is not handled properly, it
will create a serious problem to health of human beings and the environment. To
control the fire in the exposed galleries, following arrangements shall be made in
advance and with the progress of the excavation.
 The blasted galleries shall not be kept exposed unnecessarily.
 Fire fighting ranges (water pipe lines) shall be laid in an advance in de-coaled area
along the strike direction and it will be shifted as per the movement of the
extraction.
 High pressure water Jets shall be used for quenching the fire and flames arising
from coal bench.
 If fire is not controlled by water spraying, it shall be completely blanketed with O/B
or dispatched immediately after wetting with water.
SAFETY EDUCATION AND PROPAGANDA:
Safety education is very important for making awareness to all workmen,
Supervisors and Executives regarding the danger associated with the extraction of
developed pillars and precautions to be taken while operating HEMM and other
equipments. Recently, in one Opencast Mine, one dumper Operator jumped from
the dumper by seeing heavy inrush of smoke in front of dumper and fell into the pot
hole and died. If, he had well trained regarding the danger with pot hole and
precautions to be taken while working on the gallery, he could have saved his life.
He could not differentiate, whether the smoke arising in front of dumper was due to
the fire in dumper engine or it was blowing out of Pot- hole formed with tyre of the
dumper. Here, in author’s view a special training program should be arranged for all
workmen and supervisors at VTC. Every month, In-charge for compacting galleries
will conduct a safety meeting on gallery compaction and danger with the operation.

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Suggestions will be invited from the supervisors/ executives and workmen. All the
minutes shall be recorded in a bound paged book kept for the purpose.
Conclusion
To avoid collapsing of under ground galleries and bogging down of men and
machinery, effective compaction of galleries will be done to extract coal from
standing pillars by opencast method. Surveying is very- very important in U/G
turned O/C mine. The plan submitted by the U/G mine manager should be very
handy and informatic. Surveying should be conducted with latest instrument like,
Total Station etc. A dynamic leader and enthusiastic team work is required to take
all these challenges smartly.
Declaration
All the observations and comments made by the author in this paper are personnel
and not necessarily to the organization.
Date 11.08.15 Tikeshwar Mahto
Dy.Director of Mines Safety,
Bilaspur Region
07898033693
Email – tikeshwarmahto@yahoo.co.in