Practical management
Dave Cooper looks at the issue of asbestos in soil and the importance of effective air monitoring and analysis techniques to reduce exposure risks
Historical waste management and demolition practice has resulted in asbestos containing materials (ACMs) being potentially present in soil or made ground at any brownfield site. The widespread use of asbestos in building materials until it was banned in 1999 means ACMs may have been buried on site intact, broken up and mixed with other wastes and also potentially imported onto sites as a contaminant in recycled aggregates or made ground materials.
For construction and demolition companies, The Control of Asbestos Regulations 2012 (CAR 2012) places specific requirements on clients, consultants and contractors to protect workers and the general public from asbestos exposure resulting from work activities on brownfield or contaminated land development. CAR 2012 (along with the Construction Design and Management Regulations 2015) require adequate protection of any workers who may be exposed to asbestos during the investigation, assessment, management or remediation of asbestos containing soils (ACSs).
Last year, the publication of CAR-SOIL1 guidance provided additional information on achieving compliance with CAR 2012 for those working with soil and construction and demolition (C&D) materials that may be contaminated with asbestos. More recently, the Construction Industry Research and Information Industry Association (CIRIA) has also issued C7652 as a good practice site guide for all site workers who may come into contact with, or are required to manage, soils that have the potential to contain asbestos.
This latest advice focuses on practical management of ACS in field conditions and builds on earlier CIRIA C7333 guidance on understanding and managing the potential health risks and associated liabilities when asbestos-containing soils are encountered on site.
In principle, the general tiered approach to the assessment and management of potential risks posed by ACMs/ACSs is the same as that for other any other contaminant. However, the unique nature of asbestos means that different methods of analysis, exposure and risk estimation are required.
The likely airborne fibre concentrations released from asbestos containing soils will depend on the types of activities involved (hand, mechanical or pneumatic drilling etc.), the amount and type of any ACMs being disturbed and the level of mitigation measures employed.
As part of the planning system, developers are also required to undertake soil risk assessments to show the development will be safe and that the site is suitable for use. On this point the CIRIA guidance includes references to previous legal cases in relation to mesothelioma claims and reaches the conclusion that meeting the objectives of planning requirements many not be sufficient to avoid liabilities under common law.
In particular, for those involved in brownfield or contaminated land development, in order to avoid subsequent civil liabilities, mitigation measures are needed to protect neighbouring residents and the public to airborne asbestos contaminant levels which might be deemed to be significant in the future.
This is a more stringent requirement than has traditionally been required and it follows that soil and air analysis methods may need to be more detailed than those traditionally used to demonstrate compliance with CAR 2012.
This situation is increasingly being reflected by planning officials, contaminated land officers and regulators placing more emphasis on remediation strategies that incorporate scanning electron microscopy (SEM) analysis methods to fully evaluate the fibre exposure levels present.
Asbestos in soil
Higher concentrations of asbestos in soil have the capacity to liberate higher concentrations of asbestos fibres into the air, but this is also very dependent on the type of ACM present.
The release of fibres from ACMs is determined by the friability of the material and the degree of degradation and wear. In this respect, thermal insulation and asbestos insulating board may deteriorate relatively quickly, but the degradation of bound materials such as asbestos cement may take a long time.
Free asbestos at the surface can become airborne due to wind or physical disturbance during either site development phases or during site use. Soil moisture is a major inhibitor of fibre release and other factors that will reduce the release of airborne dust and fibres include dense vegetation or coverings (such as paving stones or tarmac).
CAR 2012 places specific legal duties on those responsible for works at sites where ACSs may be present and this includes site investigation and analytical techniques. The CIRIA C733 advises that where asbestos concentrations in soil are to be used to assess potential risks to human health, any analysis should be conducted using a validated method with both detection limits and quantification limits of 0.001 per cent or less.
Such quantitative analysis of asbestos in soils can be undertaken successfully using techniques based on optical microscopy. However, under some circumstances CIRIA advises that more sensitive or selective tests may be needed (eg scanning or transmission electron microscopy) – particularly when dealing with finer fibres and where there is a need for the identification of the type of asbestos present.
In addition, CIRIA also suggests that, although fibre release potential testing of ACSs is not currently a practical option it should be applied in research investigations to strengthen risk assessment capabilities.
Air monitoring and analysis
Industry guidance highlights the important role of effective air monitoring and analysis in a ‘lines of evidence’ approach to assessing airborne asbestos exposures and consequent risks to health.
When monitoring around sites with ACSs, to avoid civil liabilities, it is often necessary to demonstrate that airborne asbestos concentrations do not exceed background levels of asbestos present in the air – and it is in this process that the advantages of electron microscopy are highlighted in achieving the specificity and low detection limits required for monitoring environmental situations.
Air monitoring must be carried out under the control of UKASaccredited analysts and involves air being drawn through a filter at a known flow rate for a known period of time. The filter is treated in a manner appropriate to the analytical method to be used and the fibres are identified and counted manually using phase contract optical microscopy (PCOM). Such methods normally provide a limit of quantification (LoQ) of approx. 0.01f/cm3 but provide poor fibre discrimination (eg with non-asbestos fibres often being counted as asbestos fibres).
In terms of background concentrations of asbestos fibres, the historic widespread use of asbestos has resulted in detectable background environmental concentrations, particularly in urban areas. For example, the World Health Organisation (2002) has reported that background concentrations can be 0.0001 f/cm3 or less.
Given these concentration levels, it follows that analytical methods using PCOM are therefore not regarded as sufficiently sensitive or selective for assessing environmental exposures but may nevertheless suffice for perimeter monitoring as a first check that fibre concentrations during remediation are not out of control.
However, perimeter monitoring to demonstrate that airborne asbestos concentrations are not significantly increased by site activities will require analytical methods with a much more powerful analytical capability than that provided by PCOM.
The importance of detailed analysis and records
CIRIA guidance on understanding the risks associated with asbestos in soil points out that, as CAR 2012 continues to reduce occupational exposure to asbestos, the relative importance of non-occupational and environmental exposures may increase.
Environmental air monitoring and analysis is often used as a good practice measure to demonstrate low risks when excavations are near to sensitive areas such as residential properties.
In the future, however, the contributions of such environmental exposures to cases of asbestos related diseases may increasingly become the focus of compensation claims, particularly where obvious occupational exposures cannot be identified – although there are currently no plans for statutory regulation of such environmental exposures.
In asbestos related disease there is usually a time interval of decades after the exposure and before the onset of disease. This often means that the case investigations can run into evidential difficulties – with memories and documents being lost or imprecise. However, the judge can decide as ‘findings of fact’ matters that may be in doubt.
These findings of fact are not generally capable of challenge on appeal so it is vitally important that all documents are retained to show clearly what was done. For the person responsible in law for the asbestos-containing land, and for those on-site who have a high level of control over exposure risks, the prospects of civil litigation arising at some time in the future from a very small contribution to the asbestos exposure of someone who subsequently develops mesothelioma should not be overlooked. It is therefore important to keep all records in order to show a judge the work that was/has been carried out and to present the facts accurately.
With the monitoring and analysis of asbestos in the air, the prediction of risk requires estimates of the potential cumulative exposure to be produced. Measurement of the current concentrations of asbestos in air can be used to estimate contemporary exposures.
As a result, when carrying out monitoring around sites with ACSs, if civil liabilities are to be avoided, it will often be necessary to demonstrate that airborne asbestos concentrations do not exceed background levels.
To be representative the sampling needs to coincide with suitable site activities and weather conditions – however, the impact of false positives associated with the inclusion in samples of non-asbestos fibres can be considerable.
PCOM will give only a total fibre concentration rather than an asbestos fibre concentration, so discrimination between asbestos and non-asbestos fibres is usually facilitated by the use of more sophisticated microscopy methods utilising transmission electron microscopy (TEM) or scanning electron microscopy (SEM).
SEM with energy dispersive x-ray analysis (EDXA) allows analysts to discriminate between asbestos and non-asbestos fibres and between amphibole and chrysotile asbestos. In particular, SEM enables asbestos in air to be quantified to very low levels, achieving lower limits of detection to 0.0005 fibres / cm3 and below, compared to the 0.01 fibres/ cm3 capability of standard PCOM. TEM with EDXA and electron diffraction (ED) is even more powerful, but is more expensive and less available in the UK than SEM.
In the circumstances, in terms of understanding and managing the risks associated with the presence of asbestos in soil, the detailed analysis of air filter samples using SEM provides a powerful and more effective means of identifying the levels of exposure present and the associated risks involved.
1 Produced by CL:AIRE on behalf of the Joint Industry Working Group (JIWG) and with the assistance of and endorsement by the Health & Safety Executive, the CAR-SOIL ‘Interpretation for Managing and Working with Asbestos in Soil and Construction and Demolition Materials’ document presents a full explanation of what steps are required for compliance with The Control of Asbestos Regulations 2012 (CAR 2012). Details at www.claire.co.uk/asbestos.
2 CIRIA C765 ‘Asbestos in soil and made ground: good practice site guide’ (2017) has recently been published to give advice to all site workers who may come into contact with, or are required to manage, soils that have the potential to contain asbestos. It provides a framework to help minimise the potential health risks and associated liabilities when asbestos-containing soils are encountered on site. Details at www.ciria.org/
3 CIRIA C733 ‘Asbestos in soil and made ground: a guide to understanding and managing risks’ (2014) provides comprehensive information on the safe investigation, assessment and remediation of soil and made ground containing (or suspected of containing) asbestos fibres or ACMs. Details at www.ciria.org/
Dave Cooper works for Lucion. Lucion was established in 2002 and now operates a group of asbestos, environmental, remediation and occupational safety management activities, with a network of 11 regional offices around the country.
For more information, please see www.lucionservices.com