MEASURING THE AIR OVER PRESSURE BY INSTRUMENT WE CAN CHARACTERIZE THE AIR BLAST EVENT IN UNDERGROUND MINE.

1. Air over pressure monitoring
for characterization of airblast
events in an underground mine
GAGAN GUPTA
16152004- M.TECH (PART-1)
IIT-BHU

2. OBJECTIVE
Air Over Pressure Monitoring
The main aim of this topic is that to measure the air pressure to
classify the air blast event into different category.

3. AIR BLAST
When underground mines consist of strong and massive rock in roof and roof not
regularly cave then it leads to hang-up and leading to unsupported large extensive
area and when this roof cave then it compress the air and blow out the air in
forcing manner, this over pressure and high velocity air known as Air Blast or
Wind Blast.

4. Now we are taking two case studies and we understand the function of
Field Monitoring Equipment which is used in this case for monitoring
the air velocity, air pressure by which we can characterize the air blast
event.

5. CASE STUDY
 Moonee Colliery
(Catherine Hill Bay, New South Wales, Australia)
 Newstan Colliery
(Miller Rd, Fassifern NSW 2283, Australia)

6. LOCATION OF INSTALLATION OF INSTRUMENT
 A roof with a tendency ,proven or predicted ,not to cave regularly but hang-up.
 Little or no remnant coal in the potential goaf area in the form of pillars or stooks.
 Goaf areas having immediate roof consisting of thick, massive strata, such as
conglomerate or sandstone .
 Goaf areas having thick, massive beds above the immediate coal or shale roof but lying
within the expected height of caving.
 Goaf areas having horizontal igneous sills (associated with the boundaries of intrusive
plugs or diatremes) lying within the expected height of caving.
 Significant areas of low width to height ratio, low factor of safety coal pillars.

7. LOCATION OF INSTRUMENT IN GIVEN
CASE STUDY
Moonee Colliery

8. The configuration of longwall panel no. 3 and nearby workings and
location of the WBMS sensor pods are shown in Figure 1. Pod no. 2
was mounted on an element of the longwall equipment at a distance of
11 meters from the face and moved out-bye as the face retreated. Pod
no.4 in the main gate was located as far out-bye as possible. Pod no. 3
was located in the tailgate out-bye of the face.

9. Newstan Colliery

10. FIELD MONITORING EQUIPMENT
 Wind Blast Data Logger (WBDL).
 Sensor Pods.
 Hand Held Interface (HHIF).

11. WBDL
 It is an intrinsically unit built into a flameproof enclosure. It includes a switching power
supply with battery backup system and data acquisition unit. The system continuously
monitor the air pressure and velocity and to record the data when it exceed the preset
trigger value.
 It is a heart of system and continuously sample the output from the sensor pods at a
sampling frequency of 1000 scans per second. Trigger value is decided by the operator
including air velocity, absolute pressure and duration.
 Data from each event is recorded for 8 seconds, 2 seconds prior to trigger and 6 seconds
thereafter.

12.  Up to 16 events can be stored in it and there are 2 mode of operations fixed
and roll over.
 In former case after 16 events subsequent events are ignored and in latter
case over writing take place after 16 reading.
 Battery backup work for 16 hours after disconnection from main supply.
 Data is stored in non-volatile medium and for up to 12 months.

13. SENSOR PODS
 There are 4 sensor pods are present which continuously monitor absolute air pressure
in the range of 0 to 200 kPa and air flow pressure up to 1 kPa and velocity up to
40m/s.
 Each sensor pods comprises a cylindrical body in the form of head of pitot tube. It
consist of 2 differential transducer . Transducer at nose of the pod responds to
stagnation pressure while the other , at the cross port, responds to static pressure. The
difference between output signals from the transducer is directly proportional to the
differential velocity pressure and square of air velocity. In order to measure the
absolute pressure a direct pressure transducer is used.

14.  Power for each pod is supplied from WBDL.
 It is intrinsically safe and has high speed response for measuring
transient wind blast accurately.

15. HHIF
 It is an intrinsically safe module used to program the WBDL and transfer data
from WBDL to personal computer.
 It draw the power from WBDL via an armoured cable.
 It performs 4 main tasks while connected :-
I. Monitoring air pressure.
II. Air velocity.
III. setting trigger levels and parameter
IV. Copying data from memory of WBDL and re-starting the latter.

16.  It employs simple keyboard and an alphanumerical display for
communication and retains data in battery backed RAM.

17. AIR BLAST MONITORING
An extensive programme of monitoring was undertaken at Moonee Colliery during
the mining of longwall panels utilizing a wind blast monitoring system (WBMS)
during 1998 to 2001. Prior to Moonee Colliery, significant wind blasts had been
monitored at longwall panels only in Newstan Colliery during 1995 and 1997. Out
of the 23 events recorded in the 4 panels monitored, only eight were classified as
significant wind blasts, i.e. of sufficient intensity to pose a risk of personal injury or
of damage to the mine ventilation system.
The WBMS is certified and approved for use in hazardous locations in underground
coal mines in both Queensland and New South Wales. Its principal, operational
parameters are as follows :-

18.  Support for four sensor pods
 An absolute pressure range of 0-206.8 kPa (0–30.0psi)
 A dynamic pressure range of ±13.79 kPa (±2.0 psi), which corresponds to an air
velocity range of ±150.0 m/s (at STP) (The original dynamic pressure range of ±996
Pa (±4.0 inches water gauge) which corresponds to an air velocity range of ±40.3 m/s
(at STP) had proven to be inadequate.)
 A sampling frequency of 1 000 scans per second
 A fixed recording time for each event of eight seconds with two seconds pre-trigger
 Storage for up to 16 events in non-volatile memory.
 Eight-bit resolution

19.  Battery back-up, which powers the WBMS for 16 hours or more in
the event of interruption to the reticulated power supply.
An intrinsically safe handheld interface unit is employed to both
program the WBMS and transfer data to a personal computer for
further processing

20. DATA ANALYSIS
The HHIF containing downloaded data was taken to the surface where it was
connected to an IBM compatible personal computer via a computer interface
box. Then the data was transferred from the HHIF onto floppy disks as an ASCII
file. Subsequent analysis was carried out using Apple Macintosh computers and
included analysis and plotting air velocity and differential pressure together with
absolute air pressure in both the time domain and the frequency domain.

21. DATA ANALYSIS
Data files were further processed and graphical output produced using macros
written in Wave Metrics Igor Pro version 3.13. Standard graphical output
includes, for each measuring location, the overpressure time history together with
its integral and differential from which the impulse and rates of rise (and fall) of
overpressure are obtained. Also included in the output is the wind velocity time
history together with its integral and differential from which the excursion and
rates of rise (and fall) of velocity are obtained. The excursion is the distance
travelled by the flow of air past the sensor pod. The maximum integrated
overpressure is defined as the impulse.

22. The time histories may be smoothed as appropriate. Other graphical output, such
as the differential pressure time history and its derivatives, are generated as
required and, when necessary, a fast Fourier transform (FFT) algorithm is
employed to transform time histories into the frequency domain for further
study. Further data analysis utilizes Microsoft Excel version 8.0 and SPSS Delta
Graph version 4.5.

23. MOONEE COLLIERY
Typical overpressure time histories

24. Typical wind velocity time histories

25. NEWSTAN COLLIERY
 9 NOV 1995

26.  29 NOV 1995

27. Comparison of wind blasts at Newstan
Colliery with Moonee Colliery
The wind blast events at Newstan were localized and confined to where the
massive strata were within twice the extraction thickness and bridged the panel.
In contrast, at Moonee, incidence of large goaf falls and associated wind blasts
continued for virtually the whole length of the longwall panels other than a few
localized faulted zones where ‘regular caving’ took place. The wind blast
parameters associated with significant wind blast events at Newstan are nearly a
third in magnitude when compared to those at Moonee. The relationships
between the wind blast parameters exhibit similar trends at both collieries.

28. Although the goaf at Newstan was not accessible due to the caving of the
immediate roof, the spacing of the events, especially at LW8 panel, suggests that
like Moonee, large spans of roof were involved. The lower magnitude of the wind
blast parameters are consequently due to the following facts: the fall of the roof
element was cushioned by the caved immediate roof, lesser volume of air being
displaced from the void and also the higher resistance to flow due to partial
packing of the goaf by the prior caving of immediate roof.

30. CHARACTERIZATION OF AIR BLAST
By measuring the air velocity, air pressure, intensity of air pressure,
extent of damage or economic loss and failure of structure we can
characterize the air blast event into Highly intensive , moderate and
low category.
For this we should take accurate reading and well handling and
installation of instruments to characterize air blast into different
category.

31. Thank You

32. References
 BOCKING, M., HOWES, M., and WEBER, C. 1988, Palaeochannel development in the
Moon Island Beach Sub-Group of the Newcastle Coal Measures’ Advances in the Study of
the Sydney Basin, Proc. 22nd Newcastle Symposium, Newcastle, NSW, 15-17 April ,publ.
Newcastle: University of Newcastle. 1988. pp. 37–45.
 FOWLER, J.C.W. The Dynamics of Wind Blasts in Underground Coal Mines, Phase 1—
Interim Project Report. The University of New South Wales School of Mines, Sydney,
ISBN 0 7334 1550 4. 1977.
 FOWLER, J.C.W. and TORABI, S.R. The Dynamics of Wind Blasts in Underground Coal
Mines, Phase 3—Project Report. The University of New South Wales School of Mines,
Sydney, ISBN 0 7334 1551 2. 1997.

33.  FOWLER, J.C.W. and SHARMA, P. The Dynamics of Wind Blasts in Underground
Coal Mines, Final Project Repor. The University of New South Wales School of
Mining Engineering, Sydney, ISBN 0 7334 0700 2000.
 FOWLER, J.C.W. and SHARMA, P. Reducing the Hazard of Wind Blast in
Underground Coal Mines—Final Project Report. The University of New South Wales,