1. ASBESTOS: Sampling, Analysis & Management
19 December 2006 1

2. Asbestos identification
Some asbestos products can be recognised with experience. However, sampling products and analysing using Polarised Light Microscopy is the only absolute way of identifying asbestos products.
Dispersion staining techniques used to positively identify asbestos.
This is the physics & geology of the crystalline asbestos fibre. 2

3. PROPERTY OBSERVATION MODE
Morphology
All modes
Colour & pleochroism
Polariser only
Birefringence
Crossed polars
Extinction characteristics
Sign of elongation
Crossed polars with 1st order red compensator
RI Assessment
Dispersion staining objective with polariser only. 3

4. Process Overview
The polariser is inserted into the optical path of the microscope below the condenser.
By rotating the stage, morphology, colour and pleochroism are observed.
Insert analyser, to give crossed polars. While rotating the stage birefringence and extinction characteristics can be observed.
Insert first order red compensator (with polars still crossed) and rotate stage to determine the sign of elongation.
Assess refractive index (RI) of fibre by dispersion staining. 4

5. Morphology of asbestos fibres
Asbestiform fibres usually demonstrate the following characteristics;
An aspect ratio of between 20:1 and 100:1
Split into very thin fibrils.
Occur in parallel bundles of fibres.
Bundles have frayed ends.
Thin, needle-like fibres.
Matted masses of individual fibres
Fibres showing curvature 5

6. Colour & Pleochroism
Pleochroism is observed under polarised light and is defined as
‘A change in the colour of the fibre with orientation relative to the vibration plane of polarised light’.
i.e. A change in colour when the stage is rotated under polarised light.
This effect is caused by asbestos fibres absorbing
different wavelengths of light along and across its
length 6

7. Colour & Pleochroism
Crocidolite changes from dark blue when parallel to the polariser to pale blue-grey when perpendicular.
Actinolite also demonstrates pleochroism.
Other asbestos types do not 7

8. Birefringence
Birefringence is the numerical difference between the highest and lowest RI of a mineral.
When a fibre with more than one RI has its long axis at 45 degrees to crossed polars, interference colours are observed against the background. 8

9. Birefringence
For asbestos fibres, the interference colours depend on the birefringence and also on the fibre thickness.
Between crossed polars, a fibre with its long axis at 45 degrees to the crossed polars should be clearly visible. 9

10. Birefringence
An asbestos type has either low or moderate birefringence;
Low = grey / white colour
Moderate = white 10

11. Birefringence
Isotropic materials are not birefringent. For this reason they are barely visible under crossed polars.
Glass rods and other MMMFs are isotropic, therefore can easily be distinguished from asbestos fibres. 11

12. Birefringence
Other fibres, such as organics, show non-uniform interference along the entire length of the fibre, and incomplete extinction. 12

13. Angle of Extinction
When the stage is rotated through 360° an asbestos fibre viewed between crossed polars will disappear or ‘extinguish’ at four positions 90° apart. At 45° between each ‘extinction’ the fibre will be visible. 13

14. Angle of Extinction
Generally, asbestos fibres show complete extinction when parallel to vibration planes i.e. disappear.
Chrysotile, amosite, crocidolite & anthophyllite show straight or parallel extinction, when fibre is parallel to orientation of polariser, usually E - W or N-S. 14

15. Angle of Extinction
Actinolite and tremolite may exhibit very nearly parallel extinction. In these asbestos fibres extinction occurs at 5° to the polariser and analyser directions. 15

16. Sign of Elongation
Light passes through a birefringent asbestos fibre at different speeds along and across its length.
If the slow ray is parallel to the long axis, then fibre is described as ‘positive’ or ‘length slow’.
If the fast ray is parallel to the long axis, then fibre is described as ‘negative’ or ‘length fast’. 16

17. First Order Red Compensator
The first order red compensator is a layer of selenite or quartz.
Changes the origin of polarisation colours from zero order black to sensitive red. 17

18. Sign of Elongation
Between crossed polars, with first order red compensator inserted, the sign of elongation can be determined by observing the colours of fibres, which had previously given grey or white interference between crossed polars. 18

19. Sign of Elongation
If the fibre appears blue with its long axis pointing SW-NE the fibre is said to be length slow (Positive).
If the fibre appears blue with its long axis pointing SE-NW the fibre is said to be length fast (Negative). 19

20. Sign of Elongation 20

21. Sign of Elongation
Crocidolite is only asbestos type that has a negative sign (length fast).
However, when crocidolite is exposed to heat over 300°C, the sign of elongation may change to positive. 21

22. Dispersion Staining
Dispersion staining colours are observed with the dispersion staining objective when the fibre is parallel or perpendicular to the polariser.
Asbestos fibres can be positively identified from the characteristic dispersion staining colours they exhibit when immersed in the correct Cargille liquid. 22

23. 23

24. Asbestos identification24

25. Airborne Fibre measurement & exposure
First control limit set at 2 f/ml by British Occupational Hygiene Society
Limits gradually reduced depending on :
Medical knowledge and epidemiological studies
Practical controls in the work place.
Control limit for rare types of asbestos reduced to 0.2 f/ml in 1992
Control limit for chrysotile reduced to 0.3 f/ml in 1998
New EU directive will set Control Limit at 0.1 f/ml
No distinction between asbestos types
New limit would be same as for USA 25

26. Airborne Fibre measurement & exposure
Occupational exposure standards are in place in some countries, such as;
Japan,
Republic of Korea
Malaysia
Singapore.
Taiwan ROC 26

27. Principle Behind Fibre Counting
A measured volume of air is drawn through a membrane filter.
Filter is mounted on a microscope slide & rendered transparent.
Fibres on a measured area of filter are counted using Phase Contrast Microscopy.
Number concentration of fibres in the air is calculated. 27

28. Clearance Indicator
In the UK a value that must be achieved following asbestos removal before the area can be reoccupied.
Same levels used in Hong Kong & Australia.
Airborne fibre concentration of <0.010 fibres per millilitre of air (f/ml).
Referred to as “a transient indication of site cleanliness, in conjunction with visual inspections and not a permanent environmental level.” 28

29. Phase Contrast Microscopy
Scope : The method measures the airborne concentration of countable fibres using phase contrast microscopy (PCM). 29

30. Countable Fibres
‘Countable fibres are those deemed as respirable i.e. will penetrate to base of the lung.
The length is important, as the diameter of the macrophage is understood to be 5µm.
Countable fibres are defined as particles with :
Length > 5µm, Width < 3µm
Aspect ratio (length : width ratio) >3:1 30

31. Limitations
Fibres having widths <0.2 µm may not be visible using this method.
The PCM count represents only a proportion of the total number of fibres present.
Therefore the count is only an index of the numerical concentration of fibres and not an absolute measure of the number of fibres.
The method does not permit determination of chemical composition or crystallographic structure of fibres.
Hence - use of this method requires ALL fibres meeting the size definition to be counted. 31

32. Fibre Discrimination
It is not permissible to discriminate between asbestos & non asbestos fibres to determine compliance with the control limit or with the action level.
Therefore ALL fibres are counted. 32

33. Sampling Equipment Cowl & tubing
Open faced filter holder – fitted with an electrically- conducting cylindrical cowl extending between 33mm & 44mm in front of the filter, exposing a circular area of filter at least 20mm in diameter.
The cowl shall always point downwards during sampling.
If O rings are used – they should be made of PTFE or similar material.
Flexible tubing is required.
Cap or bung needed for cowl entrance – protects filter from contamination during transit. 33

34. Sampling Equipment
The exposed area of the filter must be known and should be measured at least every time a type of cowl or ‘O’ ring is changed. Method – use the filter holder and cowl to sample from a cloud of dark coloured dust and then mount the slide in the usual way. Two diameters measured. Diameter of the dark deposit can be measured with vernier callipers or on the stage vernier scale. Three filters in separate holders should be checked this way. An uneven appearance of the deposit may show there is a leak in the sampling head. 34

35. Slide Preparation Microscope slides must be glass:
76mm – 25mm – length.
0.8mm – 1.0mm – width.
Cover slips must be glass:
0.16 – 0.19mm thickness.
In both cases the slides and cover slips
must be clean and manufactured to
British standards. 35

36. Membrane Filters Mixed esters of cellulose or cellulose nitrate
Pore size of 0.8 to 1.2 µm
25mm in diameter with a printed grid:
1.focusing on plane of fibres
2.identifying positions
3. Facing filter correct side up on slide and in filter holder.
4. Printed grid has no part in counting
Any distortion of grid lines indicates disturbance associated with poor mounting procedure. 36

37. Filter clearing methods
Triacetin (GTA or glycerol triacetate)
Acetone vapour (and triacetin)
DMF / euparal
Others – cinnamaldehyde, other esters 37

38. Acetone-Triacetin Hot Block Method
Mounted slide will keep for years.
Slides should be kept for at least 6 months.
Hot plate temperature 50-60°C. 38

39. Filter Clearance
Filter clearance should be accomplished by the acetone/triacetin hot block method.
Just enough acetone is injected into block with an integral heater. (0.25ml)
Acetone is vaporised and emerges as a jet from an orifice below which the filter is placed.
Fine tipped pipettes or suitable droppers are needed to dispense triacetin. (120µl) 39

40. Reagents
Required for filter clearance: Acetone Excessive water in the acetone may reduce filter clarity. Glycerol Triacetate (triacetin) The Triacetin should be clean, free from dust and moisture and with no evidence of contamination/hydrolysis (indicated by smell of acetic acid). 40

41. Microscope - PCM 41

42. 42

43. Phase Contrast Microscopes
Objective lens includes
Numerical aperture
Magnification
Tube length / Coverslip thickness
Phase ring number
Eg , 40x, 160/0.17, ph2 43

44. Walton – Beckett Graticule
Graticule in one eyepiece
Graticule diameter must be known and calibrated
- 100µm + 2 µm
Area of graticule is about 1/6 of whole field of view
Mark II graticule based on 5:1 aspect ratio (not used)
Only fibres in graticule are courted
Whole field Counts have been shown to lead to under-counting (not flat field objectives)
Count 100 fibres or 200 fields (min 20 fields)
Analyst analyses approx 1.6mm2 of a filter. 44

45. 45

46. Focus on Slide
Slide not in focus
Slide in focus 46

47. Image
When the microscope is properly adjusted and optics are clean and scratch free, the image should be clear and sharp. 47

48. Image Most optics are designed for optimal performance in green light.48

49. HSE / NPL Test Slide
The HSE / NPL test slide is used to ensure that the microscopist can see fibres according to the method specification.
Place the NPL test slide on the microscope stage and focus on the lines.
On the left are a set of four coarser vertical finder lines and horizontally at the top and bottom are two pairs of horizontal finer lines.
On the right hand side of the image (next slide) the first set of contrast lines are easily visible.
The microscopist must be able to see 5 sets of contrast lines.
The sets of lines are not numbered. 49

50. HSE / NPL Test Slide 50

51. Microscope Image of Fibres51

52. Satisfactory Microscope System
Koehler Illumination
Stage micrometer
Mechanical stage with side clamps and x-y displacement
Binocular eyepieces with at least x12.5 magnification
Walton-Beckett graticule 52

53. Kohler illumination
A method of illuminating objects in which an image of the source is projected by a collector into the plane of the aperture diaphragm in the front focal plane of the condenser. This latter, in turn, projects an image of an illuminated field diaphragm at the opening of the collector into the object plane. 53

54. Fibre Counting Method Phase contrast method used since 1960’s
Depends on difference in RI between particle and filter
Depends on optical clarity of the filter
Optical microscopy is cheap, quick and easy
Some fibres missed as they are too fine
Poor accuracy at low concentrations
Problems with subjective interpretations
Fibre identification is not possible 54

55. WHO Method Length > 5µm, Width < 3µm, L:W >3:1
Count touching particles < 3 µm
Area of particulates and/or fibres < one eighth of area
Split fibres counted as single fibre
- measure width at joined part
Bundles – count fibres if distinct
- otherwise count as single fibre – usually not
countable
Fibre ends outside graticule not counted
- one end in – count as half fibre.
Counts 100 fibres or 200 fields
Evidence that WHO rules gives more consistent counts
Internal QC references shall need re-establishing. 55

56. Length / Width Example 56

57. Touching Particles - Example57

58. Other Forms of Fibre Analysis
Scanning Electron Microscopy
Transmission Electron Microscopy
EDAX 58

59. Calculation of airborne concentrations
Density – measured in fibres/mm2:for when sampling volume is unknown
F/mm2 = No. of fibres
(no. of fields) x (graticule area)
Graticule area = A = π d² 4
Where d = measured diameter in millimetre.
D = 100pm = 0.1mm hence A = mm’
Example: for a slide with 102 fibres counted in 41 fields and a graticule diameter of 102 pm (A = mm) the fibre density would be:
f/mm’ = 305
41 x 59

60. Calculations Concentrations – measured in fibres/ml
F/ml = x N x D²
n x V x 10,000
N – number of fibres
D – Exposed filter area
n – number of fields
V – Volume of air ( flowrate x sample time) 60

61. Recording results Result < 0.010 f/ml Record as <0.010f/ml
0.010≤Result Record to 3 decimal places
Result >0.015 f/ml Record to 2 decimal places
At least 80% of the results should be less than f/ml, and all should be less than f/ml. If there are four or fewer samples, all should be less than f/ml. In larger enclosures one result in five may lie between and f/ml. 61

62. Calculations Limits of Detection
A sample that is taken that has a volume <480litres the
following calculation must be implemented:
(96000 / V x No fields) x 0.01
Example:
One sample is taken from an enclosure, only 240litres
are taken and only 100 fields counted. Therefore the
following would apply:
(96000 / 240 x 100) x 0.01 = 0.04fibres/ml 62

63. Asbestos handling & management
Asbestos in a good condition can be managed safely.
Damaged asbestos should be encapsulated (painted) or removed and disposed of.
This should only be carried out using trained staff. 63

64. Asbestos handling
Operatives employed in asbestos handling should be selected from trades.
Operatives should undergo training.
Operatives to be provided with and trained in use of PPE & RPE. 64

65. Asbestos handling - RPE
Chosen with regards to suitability.
Disposable (Protection Factor x20) 65

66. RPE – Disposable P3 respirator66

67. Asbestos handling - PPE
All PPE clothing, used during removal of asbestos shall be resistant to the penetration of asbestos dust
Overalls (CE Type 5 or 6) - disposable
Overshoes
Gloves 67

68. PPE – Type 5 Overalls 68

69. Asbestos handling
Where practicable, all asbestos installations should be wetted prior to removal to minimise fibre release
Remove where possible intact
Do not drill, saw or abrade
Hand pick any pieces of debris.
Any materials used to clean debris to be disposed of as asbestos waste.
Wipe clean any tools used. 69

70. Asbestos handling Following removal, operatives must decontaminate;
Remove dust on overalls, shoes, hands using cloth.
Carefully remove coveralls by rolling inside-out.
Finally remove mask.
Dispose of all as asbestos waste in polythene bag. 70

71. Cement Products
Carry out wetting prior to removal, wherever practicable.
Remove where possible intact. 71

72. Working with asbestos Basic principles to remember
Limit the amount of asbestos fibres being dispersed into the air.
Suppress the fibres at source using control measures.
Protect yourself from the dust, even if it is a low risk material by wearing RPE & PPE.
Always take your time, don’t rush the job, it could take you longer in the end.
Try to isolate the room where you are working this will reduce any worries to the occupants of the room.
Assess the work prior to starting, there may be a better and safer way to complete the task. 72

73. Working with AC
Spray wetting using surfactants:
A portable or other type of spray can be used on some surfaces, and provided it is allowed' to "soak" into the product, thorough wetting can be achieved which will minimise any fibre release.
Once the wetting agent has been applied it is essential that the material is not disturbed until the surfactant has had time to absorb into the material.
This method can be used for suppressing surface fibre release when handling cement products, AIB, gaskets etc. 73

74. Working with AC Spray wetting using surfactants:
Spray wetting using surfactants:
Hazards and drawbacks of ‘spray wetting’ methods:
‘Wetting’ by spray should only be used where it is safe to do so, as there are some potential hazards which must be taken into consideration, which are:
electrical hazards from live plant and equipment;
the presence of chemicals and chemical contamination;
generation of steam or humidity from hot plant and equipment;
slipping hazard due to water on polythene if applicable. 74

75. Working with AC
Generic Personal Decontamination for any task
Personal decontamination is very important, exposing or contaminating other areas of the building or personnel can be very costly.
Procedures for decontamination
Clean off boots, overalls and hands using water.
Where two or more workers are present they can help each other
Remove overalls turning them inside out
Remove respirator last off all, as fibres from overalls may become airborne when removed.
Points to remember
decontaminate each time you leave the work area
visually inspect area for contamination
all waste to be disposed of as special waste 75

76. Working with AC Generic Cleaning Regime
Use a type wet rags/‘tack rags’ to clean the area of work if required
Use wet rags to clean the equipment
Use wet rags to clean the segregated area
Place used rags, debris, polythene sheeting and other waste in the waste containers
Ensure the area is properly cleaned before leaving 76

77. Asbestos handling
Cleaning of weathered roof sheet should be carried out carefully by gentle brushing & washing using biocides.
Do not power wash.
If painting, do not sand down or rub. 77

78. Asbestos waste management
Asbestos waste cannot be chemically or biologically degraded or incinerated.
Worldwide best practice is to bury waste in landfill.
Designated areas of landfill should be set aside for asbestos waste.
Asbestos waste to be separated from other waste. 78

79. Asbestos waste management
Area on landfill to be excavated for asbestos waste.
Waste to be dumped, then backfilled immediately to cover the waste.
In Maldives, on Thilafushi landfill, areas of sea are excavated and filled with waste – keeps the material wet, and land is reclaimed.
Records must be kept of locations on site, particularly where likely to be developed, such as land reclamation.
Areas of asbestos waste should not be developed in the future. 79