In this ppt you will get information about how to take mine air Sample near the sealed off area, what is COWARD'S DIGRAM, what is gramh's ratio, behaviour of gases in sealed off area

1. GOVERNMENT POLYTECHNIC, NAGPUR
( An autonomous institute of Government of Maharashtra)
TOPIC :-
SAMPLING OF UNDERGROUND MINE ATMOSPHERE
Present by :-
 Om kaitade
 Ritesh meshram
 Pratik Bramhe
 Prathmesh Bajait
 Aditya Gilorkar
 Sanket Khobragade
 Aman mure
 Sakshat Mendhe
 Himanshu Amrutkar Submitted to :-
 Nigam Uike Prof. J.T. Rawan sir

2. CONTENTS :-
 Sampling from sealed off area.
 Design of sampling pipe.
 Time and position of sampling pipe.
 Frequency of sampling.
 Methods of sampling (Sample from behind stopping).
 Methods of sampling ( Not from behind stopping).
 Behaviour of gases in sealed off area.
 Interpretation regarding condition of heating (Gramh’s Ratio).
 Interpretation regarding condition of exploxibility (Coward’s Digram).
 Reopning of sealed off area.
 Selection of methods of reopening.
 Methods of reopening.
 Precautions to be taken while reopening.
 References

3. SAMPLING FROM SEALED OFF AREA :-
Information regarding Activity of fire in sealed of area can be obtained
mainly by drawing of sample of atmosphere. From behind stopping area with
sampling pipe.
NECESSITY OF TAKING SAMPLE :-
 To study of atmosphere behind stopping.
 To know status of fire.
 Proper limit time of opening sealed off area.

4. DESIGN OF SAMPLING PIPE :-
It consists of :-
 Sampling pipe consists 5cm diameter steel pipe carrying it’s outbye.
 6mm copper plate Passes through pipe at gas-tight gland
 Steel pipe 1.5 m long
 Outbye end with socket which takes a brass plug
 Copper tube extended in bye stopping 4.5 m, supported on brick pillar to
prevent leakage of air through pipe.

5. TIME AND POSITION OF SAMPLING PIPE :-
POSITION :-
 Not near the floor, nor near the roof .
 It should be preferably 15 cm above floor, and 15 cm below roof.
 It should be midtwidth of stopping
 Extended at least 3m inside stopping
TIME :-
 When external pressure on all fire stopping equalised
 During low barometric pressure
 Between time 12 noon and 2 pm
 When barometric pressure rising water Gauge give negative reading across
stopping and fresh air will be leaking into sealed off area. Sample of this
condition not reliable.

6. FREQUENCY OF SAMPLING :-
 First sample drawn after sealing
 Sample may be collected in critical period (38-48 hrs) sealing off at 8hr
interval.
 Critical period end when oxygen % comedown to 10 % or methane % gone
above 16 %
 Therefore sampling interval may be increase to 24 hrs.
 When oxygen % falls to 5 % or less and methane % rise to 30 % or more
than frequency of sampling may reduce to once in 48 hrs

7. METHOD OF SAMPLING (SAMPLE FROM
BEHIND STOPPING) :-
Suggest 3 Methods of drawing air sample
1. SAMPLING USING GLASS SAMPLE BOTTLE AND SUCTION PUMP OR
RUBBER SUCTION BULB. :-

8. 2. SAMPLING USING GLASS SAMPLE TUBE WITH GREASED
GLASS STOP COCK AND SUCTION PUMP. :-

9. 3. SAMPLING USING GLASS SAMPLE BOTTLE AND ASPIRATOR. :-

10. MINE AIR SAMPLING (NOT FROM BEHIND STOPPING) :-
1. BY DISPLACEMENT OF AIR :-
 Bottle should be filled with clean surface water and not by mine water.
 It is preferable to fill bottle with acidified water coloured with methyl orange
 And after that open seal of bottle and allow to drop water from bottle to outside.
 Due the dropping of water air sample will come in bottle because of pressure
difference.

11. 2. VACUUM AIR SAMPLE BOTTLE :-
 By breaking neck of vaccum sample bottle at spot where sample of air is to be
collected.
 It is instantaneously filled with air sample and is sealed by rubber cap .
 Bottles are usually 250-300 cm³.
 Bottle should be labelled with place of sampling and signed and dated by sampler

12. BEHAVIOUR OF GASES IN SEALED OFF AREA :-
 The main products of combustion of coal are carbon monoxide, carbon dioxide and
water vapour.
 If fire is active % of oxygen falls quickly and % of carbon dioxide and carbon monoxide
rise sharply.
 The % of CO may rise as to much as 0.3 % to 0.4 % or more.
 In Indian mine CO, rise within 24 hrs from 0.01 % to 0.90 % and immediately on
stopping fan it shot up to 1.71 %
 And % of carbon dioxide as much as 5 % as the fires dIes out.
 As fire dying down % of carbon dioxide and carbon monoxide falls.
 There being corresponding rise in % of methane and Nitrogen.
 When fire is extinct atms. Inside sealed off area entirely composed of methane and
Nitrogen.
 If there is leakage of air % of oxygen rise and % of carbon dioxide and carbon
monoxide falls because dilution of extraneous air.
 After sealing % of methane rise up, as methane reaches 5.4 % it becomes explosive if
there is no serious drop in oxygen.
 If oxygen is less than 12.5 % mixture will be non inflammable.

13. GRAPH OF ANALYSIS FROM SEALED OFF AREA :-

14. INTERPRETATION REGARDING
CONDITION OF HEATING :-
GRAMH’S RATIO :- CO PRODUCED / O2 ABSORBED
 Use as guidance for spontaneous heating to know stage of spontaneous heating.
 Expressed in % represent fraction of oxygen absorbed as a result of heating or fire
which appears as carbon monoxide.
 IVON GRAHAM observed that this ratio increase with increasing in temperature of
coal under going oxidation.
 GRAMH’S RATIO which gradually falls to normal value for area as fire dies out
IN INDIAN COAL MINE :-
Continuous increase of GRAMH’S RATIO indicated development of heating or fire.
 The ratio of 0.1% to 0.5% indicated normal stage
 The ratio of 1% indicated existence stage of spontaneous heating
 The ratio of 2% indicated heating in advance stage approaching active fire
 The ratio of 3% or more indicated fire in active stage

15. EXAMPLE ON GRAMH’S RATIO :-
 Air enters bord and pillars panel at 10ppm Carbon monoxide and 20.78%
oxygen. Air at return panel has 80 ppm carbon monoxide and 20.52%
oxygen, calculate GRAMH’S RATIO at panel in %.
Calculation :- we know,
Air enters :- oxygen = 20.78%
Carbon monoxide = 10 ppm
Air exit :- oxygen = 20.52%
Carbon monoxide = 80 ppm
Carbon monoxide Formed = 80 ppm – 10 ppm = 70 ppm
Oxygen deficiency (absorbed) = 20.78% -20.52% = 0.26 %
Convert carbon monoxide ppm to % = 70/1000000×100 = 0.007%
GRAMH’S RATIO IN % = Carbon monoxide formed / oxygen deficienciency × 100
= 0.007 / 0.26 × 100 = 2.69%

16. INTERPRETATION REGARDING EXPLOXIBILITY :-
COWARD’S DIGRAM :-
 Is 2d graph which shows methane air mixture is explosive, or would become
explosive on addition of more methane or more oxygen.
 In this graph x-axis shows the % of methan and y-axis shows% of oxygen.
 This graph shows the limit of exploxibility with different percentage of
Methane and oxygen.
 Developed by American scientist H.F. COWARD in 1928.
 To know fire condition in sealed off area.
 Sealing off fire in gassy mine.
 Used while reopening of sealed off area.
 Lower limit of exploxibility of Methane in 5.4%.
 Higher limit of exploxibility of Methane is 14.8%.
 To make the air mixture explosive % of oxygen should not be less than 12.5%.

17. COWARD’S DIGRAM GRAPH :-

18. REOPENING OF SEALED OFF AREA :-
Before reopening mine authorities have to inform DGMS of their intention to reopen
sealed off area.
DECISION OF REOPENING DEPENDS ON WHEN :-
 The GRAMH’S RATIO has come down to value normal to seam or section, which is
between 0.1 % to 0.5 %.
 The oxygen content in sealed off area is very low (1 % or less)
 The temperature has come down to normal strata temperature, for this
temperature behind stopping area should be regularly recorded.

19. SELECTION OF METHOD OF REOPENING :-
FACTORS TO BE TAKEN INTO CONSIDERATION BEFORE SELECTING
METHOD :-
 Type and extent of fire
 Size of sealed off area
 Gas
 Time allowed for Cooling off
 Condition of doors between intake and return
 Temperature, humidity and inclination of roadway
 Accessibility of roadway
 Water

20. METHOD OF REOPENING :-
THERE ARE FOUR METHODS OF REOPENING OF SEALED OFF
AREA
THE FOUR METHODS ARE :-
1. DIRECT CIRCULATION OF AIR.
2. PRIOR INSPECTION METHOD.
3. STAGE METHOD.
4. PARTIAL RECOVERY METHOD.

21. DIRECT CIRCULATION OF AIR :-
APPLICATION :-
In which stopping are breached and hole area ventilated without previous
inspection by rescue team. As far as practicable this method should be avoided
because of hot coals may remain burried under ashes and roof falls and fire
may revive on admission of fresh air
It can be used only in case of small fires in non gassy mine area has remained
effectively for very long time, where roadway are steep, temperature,
humidity is high. A small isolated panel opened by this method.

22. PROCEDURES :-
 Establish a fully equipped fresh air base and station
rescue team here.
 Direct sufficient air by coursing to the face of a
return stopping (B) and an intake stopping (A). This
obviates the necessity of construction of air-locks
(Fig).
 Put a regulator (R) in the inbyemost connection
between intake and return.
 Breach the return stopping (B) and the intake
stopping (A). As a safety precaution, this work should
be done by a rescue team. If the stopping is provided
with a large diameter pipe, all that is necessary is to
open its blank flange.
 Adjust the regulator so as to allow only about
15m³/minute of air to enter the sealed off area; the
remaining air going direct to the return will dilute the
gases coming out from the sealed off area.

23.  Take samples of air issuing from the return stopping (B)
test half hourly intervals. This also should be done by a
rescue team. Gas testing samples analysed quickly.
 Continue circulation of air round the district until the gas
content in the return air issuing from stopping (B) reduces
to 2%.
 Send an inspection team to examine the working.
Inspection may be done by intake airway by persons not
wearing breathing apparatus but rescue must accompany
the team Any accumulation of black damp should be clear
by coursing Ventilation.

24. PRIOR INSPECTION METHOD :-
APPLICATION :-
In which whole area is inspected by rescue team before being ventilated.
It can be applied to working where high temperature,high humidity, large
extent of working and impassable falls in sealed off area make inspection
extremely difficult. If for any reason it is necessary to reopen area soon after
sealing off this method should be used.

25. PROCEDURE :-
 Build an air-tight air lock (L) outbye the
intake stopping to be breached (A). (Fig)
 Establish a fresh air base on its outbye
side.
 Breach the intake stopping (A) just
sufficient to allow the rescue team to pass.
Send the team in to inspect the whole area.
 The captain should take measurements of
carbon monoxide and methane; he should
take gas samples and temperature and
humidity readings. He should also examine
the workings for hot or warm material,
major roof falls, road blockages, water
logging, and condition of door (if any)
between intake and return. Any doors
found open should be closed. The
information gathered should be marked on
a large scale tracing of the district.

26.  Get the gas samples analysed quickly. Even if the team reports
conditions to be satisfactory, air circulation should not be attempted
until the gas sample results confirm this.
 If the whole area has been examined and the results are encouraging,
breach the return stopping (B), regulate the door of the airlock (L) to
allow only about 15m3/minute of air to enter the area, so that the
strata is cooled gradually prevention roof falls.
 If it has not been possible to examine the whole area and there is
open communication between intake and return, resort to the stage
method.
 Take samples of return of air issuing from stopping B, continue
circulation of air until the gas content falls to 2% or less. The send an
inspection party (accompanied by a rescue team) to examine the
workings. If the workings are found safe, normal work may by
resumed. Any accumulations of blackdamp should be cleared by
coursing ventilation

27. STAGE METHOD :-
The stage method in which the ventilation is restored and enclosed gases are removed in
successive stage.
APPLICATION :- :
• Where a sealed-off area is extensive.
• Where the roadways are highly inclined
• Fire seat is inaccessible
• There are connections between the intake and return airways in the area
• Fairly large influx of water in the area and
• The atmosphere in the area is too hot and humid for a rescue team to travel very far.

28. PROCEDURE :-
 Build an airtight airlock (L) out bye an intake stopping (A) an
establish a fresh air base. (Fig).
 Breach the stopping just sufficient to allow the team to pass .
Send a rescue team to inspect the area to a specified distance ,
preferably upto some 15m inbye of a connection between
intake and return . (This is no problem in bord and pillar
working).
 The distance to be covered will depend on inclination and
condition of roadways , temperature , humidity etc..
 It may be as small as 100 m in difficult conditions to as large
as 2000 m in easy condition.
 The team captain should take samples of air and temperature
and humidity readings at pre-determined points .
 He should also search for any hot or warm material and make
a note of condition of roof, floor and sides of position major
falls and any open communication between intake and return .
 The team should also select sites for temporary stopping and
measure the cross-section at each site .Access the result of
inspection and gas analysis .

29.  If conditions are satisfactory , get temporary stopping made by rescue
team . Resistance to air leakage , ease of transport of material and
convenience and speed of erection are the main requirements of the
design of temporary stopping .
 Double brattice sheet stopping with its face mud -plastered has been
used in some cases.
 Breach the return stopping (B) and erect a temporary stopping on its inbye
side.
 Open the door of the airlock (L) so as to allow only about 15m³/minute of
air to enter to ventilate the area upto the temporary stoppings. Continue
circulation of air until gas content in the return (as found out by sampling)
reduces to 2% or less.
 Dress, support and make the roadways upto temporary stoppings passable
for transport of material for brick stopping. It would be a great advantage
if transport by tubs or trolleys can be arranged,
 Select suitable sites for brick stoppings-one in front of each temporary
stopping.
 Repair the temporary stopping where necessary. It my be found
advantageous to construct G.I. corrugated sheet stopping in front of

30.  Build the brick stoppings. The stoppings (A) and (B) should be
provided with doors, and airlocks should be built in front of
them for the recovery next section of roadway.
 All work of transport of material and of building the stoppings
can be done by men without breathing apparatus but stand by
rescue team should be available. At each stopping a flame safety
Lamp should be kept burning on the floor to guard against
danger of blackdamp.
 Extend telephone, track, lightings, and shift fresh air base
equipment to the site of the new airlock (L1). Arrange for roof
support and thick stone dusting in the area recovered.
 Recover the next section exactly as the first section and continue
until the whole area is recovered.

31. USE OF BOOSTER FAN IN STAGE METHOD :-
 If the circuit of ventilation cannot be provided because
of major roof falls or too long lengths of roadways ,
erect an airlock outbye the stopping A.
 Install a forcing fan in the intake, breach the stopping A
and extend the air duct to inside of the stopping.
 The air ducts as required; this work is to be done by a
rescue team.
 The joints should be well made to keep the leakage of
air to a minimum, When the area is being ventilated,
nobody should be allowed to remain in the mine.
 The airduct will act as intake and the roadway being
ventilated as the return. When a suitable distance (100-
200 metres) reached, put a temporary stopping C.
 Ventilate the area until its gas content is reduced to 2%.
 Extendthe roadway safe, Arrange for transport of
material upto the temporary stopping and construct an
airlock in front of the temporary stopping.
 Extend the pipes inbye the airlock and repeat the
operations to recover the whole length of the roadway.

32. PARTIAL RECOVERY METHOD :-
APPLICATION :-
 In which only part of sealed off area is reopened, rest being sealed off by stopping built by
rescue brigades. This is most difficult method.It is used only when it is necessary to reopen
part of district which cannot be open fully because possible of existence of fire inside the
district.
PROCEDURES :-
 The sites of proposed stoppings are selected keeping in view the convenience of ventilating
the outer faces of the new set of stoppings and the possibility of equalising pressure across
them.
 An airlock is made on outbye side of one of the stoppings. A rescue team inspects the sites
of proposed inbye stoppings to find out their suitability keeping in view the facilities of
material transport also. The team takes measurements of cross-sectional areas at the sites.
 Arrangements are made to transport the necessary materials to the sites.
 The stoppings are built partly (in thickness) by equipped rescue brigades. Fresh air is
circulated in the area outbye this new set of stoppings. The stoppings are then quickly
completed by ordinary men. fresh air is circulated and then Pucca stoppings are built
Speedily by ordinary workers. If there is any doubt regarding air-tightness of the temporary
stoppings, atleast a part of the pucca stopping should be built by rescue teams.

33.  The pressures across the new set of stoppings should be balanced to prevent
leakage of air.
 The new set of stoppings should be provided with air sampling pipes so that a
watch can be kept on the part which remains sealed off.
 The same general precautions should be taken as in case of the Inspection and
Stage methods.

34. PRECAUTIONS TO BE TAKEN WHILE REOPENING :-
 14 days reopening notice shall be sent to regional inspector, A scheme of reopening
shall be prepared with their advice.
 Duties of different official should be specify and these should be laid down in wrriting.
 Even if rescue team are not required for reopening of work, should be available to
deal with emergency.
 Sufficient number of breathing apparatus, smoke helmet and reviving apparatus,
adequate supply of protosorb compressed oxygen, carbon monoxide detector should
be procured.
 Stone dust, wooden prop, brattice clothes, necessary Ventilation appliances, fire
extinguisher should be available in sufficiency.
 Only those persons are allowed to enter in reopening area those presence is
necessary.
 Roadway to 100m outbye fire stopping should be thickly stonedusted.
 Arrangement should also be made for speedy analysis of gas
 To know GRAMH’S RATIO gramh’s Lawrence gas analysis apparatus should be used
 Any sample giving abnormal result should be analysed twice independently to sure of
correctness of result.

35. REFERENCE :-
 Elements of mining technology volume 2 D. J Deshmukh.
 https://www.slideshare.net/NeeleshPandey14/reopening-of-sealed-off-area-
81974619
 https://www.mindat.org/glossary/reopening_sealed_area
 https://www.scribd.com/doc/118697230/Reopening-of-Sealed-Off-Areas-in-
Mines
 https://mineportal.in/blog/blog_details.php?id=92&s=gas-properties-
andamp-cowards-diagram