7.2.1 Physical properties and structure
Asbestos is a natural inorganic pollutant that can be either fibres or particulates of crystalline inorganic compounds, frequently occurring as silicates, and in most cases remain in this form. All will eventually undergo chemical weathering at various rates dependent upon the minerals within the environment. For example, quartz is resistant to natural weathering, whereas calcite particles dissolve in moist acidic environments. Other mineral pollutants such as metallic ore minerals release metal ions after weathering into the aquatic environment or into soil. The health hazards of asbestos are not due to a biochemical reaction but are due to irritational effect related to the size and shape and the surface of the fibres or particles. This may cause an inflammatory reaction within body tissues and in particular the lungs1.
Dust particles may range up to 150 microns, however smaller particles including fibres less than 10 microns in size the materials remain suspended in the air and maybe inhaled into the lungs. Particles or fibres less than 5 microns in size can penetrate into the lung tissue causing an inflammatory response.
Figure 1: Asbestos fibre size compared to human hair size
The World Health Organisation definition under current regulations defines an asbestos fibre as greater than five (5) microns in length and less than three (3) microns in width, with a length to diameter ratio of greater than three (3).
Figure 2: The size of respirable asbestos fibres, image courtesy of the US EPA.
Figure 3: Inhalation of asbestos fibres and the inflammation process
7.2.2 Historical and Current Use of Asbestos
Asbestos has been used historically in wicks for lamps, pottery, and woven items from around 4000 years ago6. The properties of this naturally occurring mineral fibre are a reason why it is still is prevalent. These properties include strength, thermal and acoustic features, it was and unfortunately still is readily incorporated into many industrial and building applications and products.
Figure 6: Asbestos mineral fibre properties and characteristics
Figure 7: Crocidolite asbestos in a natural geological occurrence, prior to mining and extraction, which is mixed with other materials to form products in industrial and building applications.
Figure 8: Chrysotile as a natural mineral fibre which is often mixed with other materials to form products in industrial and building applications.
Figure 9: Amosite as a natural mineral fibre used without additional materials as a ceiling insulation material in a residential house.
As we have seen from the health effects of asbestos, the greatest risk to health is when the asbestos fibres are disturbed and become airborne and enter through the body via inhalation and deposit into our lungs.
Therefore, when managing asbestos containing materials, we want to protect the lungs, and do not want to inhale asbestos fibres. As detailed “inhalable” asbestos fibres are very small and so we can’t rely on visual observations to determine the amount of airborne asbestos fibres.
We know we have to reduce the amount of asbestos in the air, so this is achieved by…
- Identifying if the product or material does contain asbestos minerals.
- Not disturbing asbestos material and possibly releasing airborne asbestos fibres.
- Utilising dust suppression techniques, such as water and adhesive/binding type solutions
- Using fine High Efficiency Particulate Air (HEPA) filters in vacuums, exhaust fans and in respirators/masks.
- Defining work zones including the erection of enclosures to contain the spread of asbestos fibres.
- Engineering controls to ensure that the methods we have implemented are adequate for the project, such as asbestos air monitoring.
- Personal protective equipment and decontamination procedures.
Figure 10: Examples of engineering controls for asbestos remediation works.
Figure 11: Examples of engineering controls utilising enclosures and usually under negative pressure for asbestos fibre containment during asbestos remediation works.
Figure 12: Examples of engineering controls utilising water for dust/fibre suppression to prevent airborne asbestos fibres.
7.2.4 Analysis and identification of asbestos
22.214.171.124 Naturally occurring asbestos
Most people are surprised when they hear that asbestos is a natural mineral which is extracted from the ground through mining operations. It is often believed to be a man-made product.
Naturally occurring asbestos minerals are found associated with geological deposits in rocks, sediment and soils. These fibrous minerals may be released into the air either by human activity or by weathering processes and are often overlooked as a potential source of hazardous asbestos exposure7.
Figure 13: Roadwork cutting exposing naturally occurring asbestos in the form of a Tremolite asbestos.
Figure 14: Construction activities exposing naturally occurring asbestos in the form of Chrysotile asbestos.
Figure 15: Construction activities exposing naturally occurring asbestos in the form of Chrysotile asbestos.
126.96.36.199 Commercial products or bulk samples
Many commercial and industrial products have used asbestos minerals and are mixed with other materials.
Detailed below are some of the various asbestos containing materials (ACMs) and products that are manufactured by mixing natural asbestos fibre with other compounds.
|Asbestos Bonded Cement Sheeting, may contain mixtures of various asbestos types and is manufactured by mixing with cement.||50mm by 50mm|
|Vinyl tile and linoleum floor products and adhesive glues.||100mm by 100mm, as material may need to undergo incineration overnight. Two (2) samples are recommended to distinguish the vinyl and the adhesive layers.|
|Gasket materials used on pipework, maybe manufactured with cellulose fibres or could be a woven “pure” asbestos rope style material||30mm by 30mm, ensure not to get heat damaged material as it may interfere with laboratory analysis.|
|Corrugated asbestos cement roofing materials, asbestos mixed with cement compounds, subject to weather damage and fibres maybe found in associated roof gutters||50mm by 50mm a sperate sample of the debris in the gutters is sometimes required to assist to determine the risk of the asbestos fibres being released form the cement matrix.|
|Pipe and boiler insulation, maybe encased in fabric and metal shrouds, The fabric may be woven asbestos fabric, the pipe insulation is usually mixed with magnesium silicate3.||30mm by 30mm, ensure to obtain all of the layers to the metal substrate and that the area hasn’t been replaced or repaired previously.|
|Textured coatings either for decorative/acoustic/ fireproofing purposes, asbestos may be mixed with vermiculite or paint.||50mm x 50mm multiple samples required, as was often hand mixed on site, so not always homogenous.|
|Asbestos cement pipes often underground used for water and sewerage infrastructure.||20mm by 20mm|
Table 1: Common manufactured asbestos products and the approximate sample size required for collection prior to delivery to laboratory for asbestos analysis and identification.
Sampling guidelines are as follows for the common “bulk” asbestos sample materials:
This material is often very variable in composition, particularly where it has been applied by hand. Identify patched up areas and elbows, tees near valves which maybe different to the main pipe. To gain a full thickness sample a cut down at ends or use a corer.
Asbestos cement products.
These are widely found as corrugated or flat sheeting and various moulded products such as guttering. These are usually homogenous but may have been replaced on a piecemeal basis. Samples should be taken from a damaged area or discrete location at an edge or corner.
Thermoplastic floor tiles.
Samples can be obtained by cutting a small section or corner of the tile. One sample of each type or colour is usually sufficient. Where a tile is layered a sample of each layer along with any adherent glue must be included.
Asbestos insulating boards.
These boards or tiles are usually homogenous but may have been replaced on a piecemeal basis, so all areas should be sampled.
This material is usually homogenous, so unless there are areas that appear different, two samples (one at each end) would usually be sufficient.
Textured (decorative/vermiculite) coatings.
These pose particular problems for both sampling and analysis. It is impossible to tell from appearance whether or not they are likely to contain asbestos. Also, if present it is usually only around 1%. As a result, it is necessary to sample a reasonable amount of material by scraping off with a chisel an area of about 10-20cm². Some surveyors prefer to make a composite from 4 or 5 smaller areas in a room.
188.8.131.52 Asbestos in Soils
Asbestos may be found in soils from naturally occurring geological occurrences or from anthropogenic activities.
Figure 16: Anthropogenic activities of buried asbestos materials or redundant infrastructure may cause significant project delays and during unexpected finds may potentially expose people, if not identified early and managed correctly.
Figure 17: Illegally buried and corrugated asbestos cement sheeting, disturbed and exposed during construction activities
Figure 18: Residential house construction disturbing naturally occurring asbestos minerals.
Figure 19: Construction site known naturally occurring asbestos geological area, excavations appropriately managed, using exclusion zones and dust suppression techniques.
Figure 20: Roadwork cutting exposing naturally occurring asbestos in the form of Chrysotile and Tremolite asbestos.
7.2.5 Asbestos air monitoring
We undertake asbestos air monitoring where people are likely to be exposed to airborne asbestos. Most likely in an asbestos removal/remediation or workplace activity; the air monitoring location is where employees and the public may have the potential to be exposed to asbestos.
Samples are collected using a sampling pump, which draws a measured quantity of air through a prepared membrane filter cassette. The membrane filter is then treated using an acetone generator to be transformed into a transparent optically homogeneous specimen. Using phase contrast microscopy, the fibres on the transparent filter are counted and sized according to set criteria. The counted fibres are then placed into an equation to determine the air concentration which is reported as fibres/ml of air in some countries including Australia.
When a sample(s) is received into the laboratory it should be accompanied by a Job Site Work Sheet/Chain of Custody (COC), which will have, details such as the project reference number, client details, date of sampling, site of each sample collection, an individual identifying sample number of each sample, rotameter number, batch number of canisters, sampling pump identifiers, time the sampling started and ended, and flow in litres/min for the start and the end of the sampling period and whom undertook the sampling, an example of a COC is detailed below. Of note in the field each canister should be checked and matched, carefully to the paperwork.
Figure 21: An example of asbestos fibre chain of custody.
184.108.40.206 Asbestos para-occupational or control air monitoring
When undertaking air monitoring consider areas where personal protective equipment (eg. respirators) are not required, for example surrounding the asbestos working zone. Measuring these air levels will ensure that the engineering and control processes that have been designed are adequate for the type of project you are undertaking. This form of asbestos air monitoring is referred to as para-occupational or control (asbestos) air monitoring.
This type of monitoring will not measure personal exposures, this type of occupational or exposure air monitoring is discussed in the next section. Consideration of the vertical height of the sampling head needs to be considered, for example if in an office area adjacent to the asbestos works the sampling head height would be set at approximately 1.0m from the ground to represent a section of the breathing zone height as people are sitting. If the asbestos air monitoring is outside the exclusion zone of the asbestos works where people are walking past, the sampling head height would be set at approximately 1.8m from the ground, again representing the breathing zone of people walking past the asbestos zone. It is therefore important that the selected location is representative of the immediate environment. Once the location has been made, the filter holder must be secured to the mast at approximately breathing zone height.
Examples of locations where para-occupational asbestos air monitoring static sampling points maybe positioned could be;
- The immediate exit point when the respirator is removed after the decontamination process.
- Contractors or employees lunch/crib rooms
- Inside heavy machinery cabins involved in the asbestos works
- Vulnerable points of the asbestos remediation enclosures for example negative air pressure exhaust exit areas, or waste decanting areas.
- Around the asbestos remediation zone, for example North, South, East and West, and floors above and below, people egress zones such as elevators.
Sample duration time is influenced by a number of factors including the reason for sampling, level of fibre concentration to be measured and general non-fibrous dust levels. The total sample duration should never be less than four (4) hours for exposure and control monitoring. The sample duration should, preferably be over an entire working shift.
Please see the link below about the process of setting air monitoring equipment in the field (para-occupational or control air monitoring) and the process to getting the sample to the laboratory for analysis.
220.127.116.11 Asbestos occupational or personal exposure air monitoring
As discussed above with para-occupational or control asbestos air monitoring we are not measuring what people are exposed to; this is undertaken by occupational or personal exposure air monitoring.
When we are considering people working around asbestos on a daily basis, we would perform occupational or personal air monitoring to understand what amount of asbestos the individual is breathing or inhaling over an eight (8) hour working day over a standard forty (40) working week. This airborne level is then compared to Workplace Exposure Standards (WES).
The sampling pump is attached around the waist, with the tubing extending up over the shoulder and secured so the person may work unencumbered, with the sampling head positioned on the shirt lapel within their breathing zone. The worker’s breathing zone (300mm hemisphere in front of the face, measures from a line dissecting the ears). The filter canister should always be facing downwards.
Figure 22: Para-occupational or personal asbestos air monitoring at known naturally occurring asbestos geological occurrences in an agricultural occupation.
7.2.6 Interpretation of laboratory reports
18.104.22.168 Collection of “bulk” asbestos building product samples
If sampling suspected friable asbestos, air monitoring should be undertaken during the sampling period. Never sample electrical backing boards due the risk of electrocution, other safety factors should be considered such as heights, confined spaces.
When sampling “bulk” building materials prior to transportation to the laboratory the following procedures should be adopted and the area prepared prior to obtaining a sample for laboratory analysis. A plastic sheet should be placed below to catch any loose material that may fall off during sampling, a respirator and other personal protective apparel may be required such as disposable coveralls and booties and gloves, this is dependent upon the material being sampled. Prior to sampling ensure all air conditioning is isolated to the sampling area or if in an external environment and the conditions are too windy, the sample collection may need to postponed until climatic conditions are ideal. The immediate sampling area should be dampened down with a water spray bottle and collection of the sample should occur ensuring that equipment to obtain the sample is clean to ensure no cross-contamination, place the sample into a resealable plastic bag, label with the project details, date, individual sample identifier and the sample location and the type of material being sampled. Double bag samples prior to transportation to the laboratory and ensure external packaging is robust and secure to be safe during transportation to the laboratory.
Please see the video link below on how to safely collect a sample prior to transportation to the laboratory.
22.214.171.124 Quality control and limitation of samples
The biggest error in the identification of asbestos in “bulk” samples and with asbestos air monitoring is likely to occur in the fieldwork.
Samples collected for identification need to be large enough to be a representative sample to truly reflect the overall material. Errors may occur with sample collection with cross contamination or incorrect labelling. Sometimes materials were mixed on-site especially vermiculite material so they may not be homogeneous in nature so composite samples maybe required to be collected on-site. Interpretation of the chain of custody used in the field and the laboratory reports should be reviewed with these considerations in-mind.
Asbestos air monitoring limitations usually occur with volume measurement. The total volume of air that passes through the membrane filter needs to within the optimum testing parameters generally between 400 to 600 litres of air.
|1.0 L/min||8 hrs (480min)||480L|
|2.0 L/min||4 hrs (240min)||480L|
|3.0 L/min||3 hrs (180min)||540L|
|4.0 L/min||1 hr 40 mins (100min)||400L|
|5.0 L/min||1 hr 20 min (80 min)||400L|
Table 2: Flow-rate requirements i.e. Volume of air required is between 400 to 600ml collected
Additionally, the internal sampling pumps flowrates are not generally accurate nor calibrated, so external calibrated rotameters need to be used, as per the diagram below.
Figure 23: Sampling train example utilising an external calibrated rotameter to ensure correct flowrate at the beginning of the sample period and at the end.