Sampling of dust

Sampling of dust

1. 1

2. SAMPLING OF DUST
2
•Suitable preventive and
suppressive measures for allaying
dust in amine
•it is essential to have a suitable
device to estimate or sample air-
borne dust likely to be breathed
by miners.

3. •The following facts must be
considered in the choice of a
sampling instrument:
Knowledge of the necessary dust
concentration in the dangerous size
range.
Mass concentration of the respirable
fractionof dust is widely accepted
relevant standard.
3

4. •But MAC is not an agreed international
standard
•as conclusive correlation between
different dust parameters and incidence of
pneumoconiosis uniformly applicable to all
types of dusts is not established yet,
4

5. particle concentration with particle-size-
frequencydistribution and surface area
concentration still continue to be assessed
Also the sample should be able to give an
assessment of the dangerous component of dust
as regards composition.
This necessitates adequate volume of sample for
chemical and mineralogical analysis.
5

6. •The duration of the sample should be such
as to give a true picture of dustiness of
any mining operation or place or work with
optimum number of samples to be taken.
•The sample should be continuous over at
least a workingshift.
•The sample should be representative of
the dust cloud in the breathing zone of the
worker.
6

7. SAMPLING INSTRUMENTS
•The sampling instrument should be easily
portable and
•robust forrugged underground conditions and
•require minimum maintenance
•need minimum operational skill
•self-contained power supply
•render the measurement of dust in as little time,
as possible without involving too much
accessory work.
7

8. •more precise and accurate instruments for
dust sampling are essential for laboratory
and research work,
•for routine dust analysis it is a
compromise between accuracy on one
hand and cost, skill in operation, time and
easy manipulation on the other.
8

9. DURATION AND INTERVAL OF
SAMPLING
•Dust generation in any mining operation
varies a great deal with time
•the variation is greatly irregular due to
irregularities in normal cycles of operation.
•the time and duration of sampling should
be very carefully chosen to give a fairly
accurate estimation of the dustiness of any
particular operation over a long period.
9

10. •A true estimate can however be obtained by a
continuous sampling device working over the
whole shift or even over several shifts.
•From this a true shift mean or, in general terms,
a true period mean can be obtained.
•A mean close to the true period mean can
be obtained by taking a large number of short-
duration samples over the period,
•the deviation approaching zero as the number
approaches infinity but it is impracticable.
10

11. •Snap samples or samples taken over a short
duration are liable to deviate a great deal from
the true average at a source dust production
owing to large variations in the rate of dust
production at the source and
•to get a close approximation to the true mean,
a very large number of samples will be
necessary .
11

12. •Studies suggest that a sampling period of
ten minutes will reasonably represent the
true mean with the result falling within
•20% or the average in two out of three
cases.
12

13. POSITION OF SAMPLING
•Dust production in any mining operation is
intermittent and the irregular and depends
on the nature of air movement and the
dust distribution at the face,
•It is difficult to select the correct part of the
face where a true representative sample
can be obtained
13

14. Samples taken at different sections of the
working face near the source of production of
dust show wide variation .
Due to the longitudinal and lateral mixing of the
dust in the air-stream, the variations gets
gradually attenuated as the sampling points are
receded farther along the return airway,
14

15. If the Reynolds number characterizing the air-
flow is well above the critical number which is
generally the case with any ventilation system,
complete mixing takes place at a distance, of
five to ten roadway diameters
•It is possible to get a more average dust sample
beyond the mixing zone than near the source,
15

16. •Any temporary variation in dust production
at the source tends to be attenuated with
increasing distance from the source,
•Due regard of course is to be paid to any
admixing with dust from other sources.
16

17. •With velocities prevalent in mine airways,
gravitational settling of dust is slow,
particularly so for the pathogenic size of
< 5 µm and it is possible to get a
representative sample at a distance of
6 to15 m away from the face.
•Uniformity of distribution in an air-stream
is dependent on the uniformity of flow in
the airway.
17

18. For getting a representative sample, it is
necessary to collect the sample in a straight
position on of the air way at least ten diameters
away from any bend or major obstruction.
when collecting a sample of dust from air the
samplingvelocity should be as far as
practicable, equal and uni-directional to the
velocity of air from which the sample is being
collected. This is essential for minimizing the
loss of particles by inertial separation before
entry into the sampler.
18

19. •The best sample having direct relevance to
health hazard is one collected at the breathing
point of the worker.
•This has led to the development personal dust
samplers which collect a sample of the
respirable dust fraction over a sufficiently long
period, usually a shift
19

20. METHODS OF SAMPLING
•Based on the principle of air-borne dust
Sampling methods can be classed as follows:
•(a) filtration,
•(b) sedimentation.
•(c) inertial precipitation,
•(d) thermal precipitation,
•(e) electrical precipitation ,and
•(f) optical methods based on light scattering,
20

21. •Filtration has been the earliest method of
sampling.
•Sugar tubes -had only 87 % filtration
efficiency by weight for silica dust and a
fair amount of fine dust of the respirable
size range escaped collection
21

22. •Other soluble filtering media like potassium
nitrate, salicylic acid etc. were tried to improve
filtration efficiency.
•Non soluble filters tried were of cotton ,wool,
flannel etc.,
•Synthetic membrane filters having pore size
down to 0.01µmhave been developed.
•Paper thimbles claimed to have 98 % filtration
efficiency.
22

23. Filtration was primarily used to collect large
samples of the order of 50mg or more for
chemico-mineralogical analysis.
Mass concentration could be determined by
differential weighing of the filter before and after
collection of the sample,
But, this concentration was of little value since it
covered the entire particle size range, i.e.
inclusive of all the particles above the respirable
size range
23

24. •Attempts have been made to obtain the mass
concentration in the respirable size range from dust
samples collected on soluble filters, by dissolving the
filters and separating the < 5µm particles by
sedimentation.
•This does not give the picture of the mass concentration
of the respirable fraction in the air-borne dust since the
aggregates present in the air-borne dust cloud which are
normally treated as single particles of the aggregate size
in the respiratory system,
•Dust particles break up in the process of solution and
separation and so an overestimation of the mass
concentration of the respirable fraction is obtained.
24

25. Particle concentration
•Particle concentration and size distribution have
been determined by spreading a certain amount
of dust collected on the filter on a glass slide in a
solution of Canada balsam in xylol (the dust gets
fixed in Canada balsam when the xylol
evaporates ) and counting it under a
microscope.
•But proper dispersal of dust on a microscope
slide by this method is difficult and errors creep
in due to both small particles flocculating and
aggregates breaking up.
25

26. •Other Instruments based on the principle
of filtration include the Soxhlet and Gothe
filters which use paper thimbles,
•Siter filter using a synthetic membrane
filter and the microsorban filter using a
low-resistance soluble filter.
26

27. •Filtration has become important in recent
times due the adoption on of the mass
concentration of the respirable size
fraction as the relevant dust parameter
signifying health hazard.
•The samplinginstruments commonly
known as gravimetric dust samplers
27

28. Gravimetric dust samplers
•Use an elutriator of gravitational settling or
cyclone type which separates out dust particles
above respirable size range.
•The respirable size fraction is collected on a
membrane or glass fibre-paper filter in a suitable
holder.
•The filter can be weighed before and after
sampling to get the mass of dust collected.
28

29. •Now a days pre-weighed filters are
available to avoid double weighing.
•These are of two main types of gravimetric
dust samplers :
(a) those using a gravitational-settling type
of elutriator and
(b) those using cyclones for elutriation.
29

30. Respirable dust monitor RDM-201
•This is a gravimetric sampler
developed in the U.S.A. which gives an
automatic digital readout of the mass
concentration of the respirable dust by a
beta-ray absorption technique.
30

31. •The instrument comprises a cyclone
elutriator which separates the coarse
fraction and a filter which collects the
respirable fraction.
•The mass, of dust deposited on the filter
per unit area is obtained from the
absorption of β radiations from a carbon-
14 source as measured by a Geiger
counter.( Radio activity measuring
instrument)
31

32. Sedimentation
•Green'" utilized gravitational settling for
estimating the dust content of air.
•A certain volume of air is caught in a
vertical cylinder and the dust in it is-
allowed to settle by gravity on to a glass
slide placed at the bottom of the cylinder.
•The slides are then examined under the
microscope for determining particle
concentration and size.
•.
32

33. •Control the temperature of the cylinder
essential to avoid convectional air
movement inside the cylinder for accurate
results.
•This method has been claimed to give
almost 100% efficiency for particles
greater than 0.2 m size, but it requires a
long time of settling under rigorous
laboratory condition
33

34. .
•The slotted-duct dust sampler, developed
by Boddy'" is a long-duration sampler
based on the principle of sedimentation.
•However, the sedimentation method
requires tedious microscopic counting and
sizing and is subject to personal error.
34

35. Inertial Precipitation
•Dust sampling instruments using inertial
precipitation are based on three principles:
•Impaction.
•Impingement and
•Centrifuging.
35

36. Impaction.
Certain volume of mine air is made to
impact on a glass slide coated with a
suitable dust collecting adhesive.
The dust which gets deposited on the slide
is counted under a microscope.
konimeter is an example
36

37. Impingement
•A measured quantity of the dust-laden air
from a nozzle impinges on the bottom of
the flask and the dust is collected in the
collecting fluid.( Velocity is about 7 m/s)
•A portion of the dust-laden fluid is filled
into a counting cell usually 1 mm deep
which is then covered with a cover slip.
•The cell is allowed to stand to allow the
dust particles to settle to the bottom or the
cell and counted under a microscope.
•Midget Impinger is an example 37

38. •Centrifuge is based on the principle of
centrifuging.
•The is instrument collects a size-graded
spectrum of dust, but its high speed of
rotation confines it to the laboratory only
38

39. THERMAL PRECIPAITATION
•This method utilizes the principle that when a
body surrounded by dusty air is heated, a dust-
free zone is produced around the hot body,
•The extent of the dust-free zone depends on the
temperature gradient between the hot body and
the surrounding air.
•If such a zone is intercepted by two glass cover
slips and a current of dusty air allowed to enter
the space between them the dust in the air gets
deposited on the cover slips where it remains
attached by molecular attraction
39

40. •The dust particles collected on the cover slips
are counted under the microscope
•The thermal precipitator has a high collection
efficiency.
•The low velocity of sampling does not break up
aggregates and a fairly representative sample
over a reasonably long duration is obtained.
•Microscopic counting of the dust particles is
tedious and subject to personal error
40

41. •Automatic electronic devices have been
developed for counting and sizing of dust
samples collected by the thermal precipitator.
•A diffraction size-frequency analyzer developed
has been claimed to give an accurate measure
of the size distribution of the dust sample as well
as the respirable surface area of the
41

42. Electrical Precipitation
•Electrical precipitator essentially consists of a
charging wire maintained at a high negative
potential of about 12000 volts and surrounded
by an earthed concentric cylinder.
•Dust-laden air is drawn through the cylinder by a
fan at a constant rate.
•The dust particles when passing through the
instrument, get charged and are drawn to and
precipitated on the inner surface of the earthed
cylinder..
42

43. •This instrument, like the filtration devices, has a
large sampling capacity and is suitable for
collecting large quantities of dust for chemical
analysis.
•The mass concentration can also be determined
by noting the difference in weight of the cylinder
before and after collection of dust.
•The instrument has a high collecting efficiency,
but the high voltage used in it makes it
unsuitable for use in coal mines underground .
43

44. •Gravimetric dust samplers utilizing
electrical precipitators have been
developed where the coarse fraction of the
air-borne dust is first removed in a cyclone
separator and the respirable fraction is
collected in the electrical precipitator for
estimation of mass concentration by
differential weighing.
44

45. Optical Method
This method utilizes the property of scattering of
light by suspension of fine particles
•For particles large enough compared to the
wave length of light i.e., particles above 1µm in
diameter the intensity of scattered light is
roughly given by the relation
45

46. •
•where
•Is -intensity of scattered light,
• 1ointensity of incident light,
• N number of particles per unit
volume,
• D diameter of particles
K is a constant depending on the refractive
index, absorption coefficient ,shape of the particles
as well as the wave length of light angle of
scattering and the distance of the point of
observation from the dust cloud
46

47. •The equation shows that the intensity of
scattered light is proportional to the
surface area of the particles, a fact well
established in practice.
•Tyndalloscope ia an example
47

48. OPTICAL-Holographic
•Holographic System:-A different optical system
which has been developed for counting and size
analysis of a suspended cloud of aerosols.
•Consists of a pulsed ruby laser illuminating the
particles.
•The light diffracted from the cloud forms ring-like
wave interference patterns on a photographic
film which gives a permanent record of these
patterns called the hologram.
48

49. •A three dimensional dust cloud is
reconstructed from the holgram by another
laser beam.
•This can be magnified 300 times by a
Vidicon camera tube and television
monitor.
•Individual particles can be focused and
displayed on a screen for visual analysis.
•However, the existing instruments are
capable of recording particles above 3 µm
size only and hence are not suitable for
mine-dust analysis.
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50. Location of dust sampling
•For fixed point 'area sampling' (also
sometimes referred to as static sampling),
the location is so chosen as to obtain
representative concentration
of respirable dust associated with dust
generating sources.
50

51. •The National Dust Prevention Committee
for coal mines in India by its
recommendation of 1993(21) gave
sampling locations for area sampling in
•(a) bord and pillar,
•(b) long wall,
•(c) drivage, and
•(d) opencast workings and surface plants .
51

52. Bord and Pillar workings
•(i) Intake airway of a working district within 20 to
30 m of immediate out-bye ventilation
connection from the first working face
•(ii) Return airway of a working district within 20
to 30 m of immediate out bye ventilation
connection from the last working face
•Where there is more than one return airway, all
the return airways are to be sampled.
•iii) Working place or face where dust
concentration is likely to be maximum .
52

53. •(iv) Resting place of workers.
•(v) 3 to 5 m on the return side of other places
where substantial dust is generated, e.g.
loading/transfer point
•(vi) Main return airway of the mine.
•Long wall workings 30 m out bye of the face in
the intake airway
(ii) at the centre of the face and
•(iii) 50 to 70 m out bye of the face in return
airway
53

54. Drivages or long headings
•Sampling shall be done in the drivages
when they are driven more than 30 m or
when the system of working is fully
established to enable collection of a
representative sample.
54

55. Opencast workings / surface
plants-
•(i) Samples should be taken at the working
places near workers.
•(ii) In surface plants like coal handling
plant (CRP), crusher house, siding and
other places n processing plants where
dust is generated.
55

56. •In opencast workings, sampling by
personal dust samplers is considered
more reliable than sampling by fixed-point
samplers.
56

57. •Sampling time for a static sampler during a
working shift is defined as the starting of
the sampling instrument as soon as the
first man arrives at the work place and
switching off the instrument when the last
man leaves the work place.
57

58. •. During shot firing a sampling instrument sited
near the face may get damaged and hence has
to be removed along with the workers leaving
the face, but the instrument should remain
switched on and be relocated at the
same place when work resumes at the face.
•As the instrument is generally removed to the
intake to a site with very low dust concentration
the time weighted average (TWA) dust
concentration of a place should be calculated
on the basis of the face working time only.
58

59. •The frequency of respirable dust sampling
is specified as once at least every six
months in CMR 1957.
•The maximum interval between sampling
is reduced to three or one month when the
dust concentration exceeds fifty or seventy
five percent respectively of the allowable
value
59

60. 4.0 Sampling procedure
•4.1 Places to be sampled
•4.1.1 General: As required under Reg. 123
(3)(a) & (c) of CMR 1957, all the workplaces in a
mine, where respirable dust is evolved, shall be
sampled to ascertain the air borne dust
concentration of that area and the dust exposure
profile for different categories of work persons
working in that area.
•In view of the above Manager of every mine
shall identify such places in the mine.
60

61. •Mine air of that area shall be sampled by
'static sampling' method by a fixed type
sampling instrument.
•This shall be cross checked by measuring
the dust exposure of selected workers,
whose exposure is deemed to be
representative of their groups, by 'portal to
portal personal monitoring' by using
personal dust samplers
61

62. 4.1.2 Fixed point or static sampling
for underground workings
•The following places shall be sampled by
fixed type samplers or static samplers:
•(a) For B & P or R & P workings : The
sampler shall be positioned on the return
side of the point of dust generation (and
within 1m of the normal working position
of, but not behind the operator or worker)
in the following places-
62

63. •Within 30m out bye of the first working
face in the intake side of the district.
•30m out bye of the last working face in the
return side of the district
•Working faces
•Loading / Unloading / Transfer points
•Bunkers / Chutes
63

64. b) For Longwall working
•30m outbye of the face in the intake
airway
•10m from the intake end at the face
•10m In bye from the return end of the face
At the-centre of the face
•30m out bye of the face in the return
airway
•Loading / Unloading / Transfer points
•Bunkers / Chutes
64

65. c) For Mechanized Long wall gate
roads
•10m out bye of the face
•30m out bye of the face
•Loading / Unloading / Transfer points
•Bunkers / Chutes
65

66. 4.1.3 Personal Dust Sampling for
underground workings
•In addition to the static sampling as above, dust exposure to the
following categories of persons shall be determined by personal
dust sampler
•Loaders
•Shotfirers and helpers
•Drillers / Dressers
•Operators and helpers of loading machines (SDL, LHD, Shuttle cars
loaders or other mechanical loaders)
•Operators of Cutter loaders ( Shearer, Plough, Continuous miners,
Road headers etc.,
•Longwall face-crews
•Conveyor. bunker or chute operators
66

67. 4.1.4 Fixed point or static sampling for Opencast
workings surface operations
•Direction of air current should be kept in mind
and the instrument be placed on the return side
of the 'point of dust generation.
•It is suggested that more than one fixed-point
sampler shall be installed along the
circumference of concentric circles of 5m & 10m
radius around the point of equipment generating
dust.
•The sampler shall be installed along the
direction of wind or air current and the samplers
may change their location during sampling with
change of direction of the air current.
67

68. •However, in opencast workings, sampling
by personal samplers is considered more
reliable than sampling by fixed samplers.
68

69. 5 Personal Dust Sampling for open
cast working and other operations
•Dust exposure of the following categories
of persons shall be determined personal
dust sampler :.
•Drillers & helpers
•Operators of excavators/loaders (Shovel,
Back-hoe, Dragline, Front-end loaders)
69

70. •Dumper & Tipper operators & helpers
•Dozer/Grader operators & helpers
•CHP crews, crusher operators & helpers,
wagon loaders
•Any other machine operators.
70

71. •Sampling with MRE or its equivalent should be carried
out with air inlet of the Instrument facing the air current
keeping the instrument in horizontal position,
•If the velocity of air is less than 4 metre per second
and perpendicular to the air current,
•if the velocity of air is more than 4 metre per second. The
instrument shall be placed at about breathing level
with normal posture of the operator and located centrally,
and away from the side, as far as practicable.
•Safety of the instrument and interference of the normal
work shall be kept in mind for positioning the instrument.
71

72. 4.3 Frequency of dust sampling
•(a) As required under Reg. 123(3) (a) of CMR
1957, every place as mentioned above shall be
sampled by fixed point samplers, at least once
in every six months.
•Provided that if any measurement of any work
place shows the concentration in excess of 50%
of the permissible limit, the subsequent
measurement shall be carried out at intervals
not exceeding 3 months.
72

73. •Provided that if any measurement of' any
workplace shows the concentration in excess of
75% of the permissible limit, the subsequent
measurement shall be carried out at intervals
not exceeding one month
•(b) Such measurement shall also be carried out
immediately upon the commissioning of any
plant, equipment or machinery or upon the
introduction of any new work practice or upon
any alteration therein that is likely to bring about
any substantial change in the levels of airborne
respirable dust.
73

74. •(c) If respirable dust concentration exceeds the
permissible limit, then the area shall be sampled
again for 5 times in the next 7 successive normal
working shifts according to the provision of Reg.
123(4) of CMR 1957 and continued till the
permissible concentration comes within limit
•Once the respirable dust concentration falls to
permissible limit or below, the places shall be
sampled as required under clause 4.3(a).
74

75. •4.4 Sampling by personal dust sampler
shall also be carried on along with
fixed point sampling to have a cross
check.
75

76. Rejection of samples
•A sample shall be rejected in the following cases:
•If the instrument was not working throughout the entire
shift of 8 hours.
•If duration of operation in that area, including operation
of the machine which generates dust, in that particular
shift is less than 80%' of normal duration of operation
in a shift (average duration of operation of previous one
month) of that area.
•In case of 'portal to portal' sampling, if the person to
whom the personal
sampler is attached does not do his normal work in that
shift
76

77. 5.0 Recording of results
•All results of measurements of air borne respirable dust and all the
relevant particulars shall be recorded in accordance with Reg.
123(3) (f) of CMR 1957.
•5.1 A plan in a suitable scale should/be maintained showing clearly
all the places where sampling of air borne dust has been done.
Date 0f last sampling should be indicated on toe plan,
•5.2 Results of air-borne dust survey shall be maintained in the
format per annexure I & II.
•5.3 Record of respirable dust content and the Quartz content shall
maintained in the enclosed format and kept in a bound paged book
•5.4 Details of the weighing balance used shall be recorded along
sampling data.
77

78. 6.0 Preservation of filter papers
•The filter papers used for a particular
sampling shall be preserved along with its
serial number and date of sampling.
•These filter papers be. preserved at least
for a period of 3 years and shall be readily
available to the Inspector of Mines if so
desired
78

79. 7.0 Report on Air Borne Dust
Survey
•After conducting the air borne dust survey as per
the above guide report shall be prepared giving
the following details
•(i) Introduction
•(ii) Methodology of dust sampling
(a) Sampling strategy for static sampling
(b) Sampling strategy for personal sampling
(c) Instrumentation
79

80. iii) Observation
(a)Tables showing the results of air borne
dust survey for static and personal
sampling.
(b) Maximum dust concentration and Time
Weighted Average( TWA ) for different
locations.
iv)Conclusions.
v)Recomendations
80