How do you calculate asbestos levels when air testing and monitoring?
Asbestos air testing and monitoring plays a critical role in the responsible management of the now-banned mineral across a broad range of sites. As part of this, it is hugely important to accurately calculate the exact level of airborne asbestos in a particular location, or that a specific individual is breathing in.
Such accurate calculations of the concentrations of asbestos fibres in the air, will inform the subsequent decisions made to ensure safety and legal compliance at the given premises.
In this article, we have sought to provide a detailed explanation of the methods and procedures for calculating asbestos levels during air testing. Below, then, are the essentials to know.
Importance of accurate asbestos level calculation
Having first been commercially mined in the middle of the 19th century, asbestos went on to be extensively used in UK industries such as construction and shipbuilding. The naturally occurring substance was prized back then for such qualities as its relative affordability, physical strength, fire resistance, and effectiveness as an insulator.
So, for the bulk of the 20th century, asbestos was incorporated into items including – but not restricted to – asbestos insulating board (AIB), asbestos cement roof tiles, asbestos vinyl floor tiles, and sprayed coatings.
By around the 1970s, however, it was becoming increasingly undeniable that the inhalation or ingestion of asbestos was driving up the risk of exposed individuals developing potentially fatal health conditions, such as mesothelioma and asbestos-related lung cancer.
Indeed, the several-decades-long latency period for the emergence of asbestos-related disease helps to explain why, even during the 2020s – more than a generation after the 1999 ban – approximately 5,000 people a year die from asbestos-related conditions in the UK.
Political pressure to act on such clearly severe health risks culminated in all forms of asbestos eventually being outlawed in the UK. Fast-forward to today, and the UK has a stringent legal regime in place for the management of asbestos across a wide range of non-domestic premises, as set out by the Control of Asbestos Regulations 2012 (CAR 2012).
Indeed, Regulation 19 of CAR 2012 stipulates that employers must arrange for the regular monitoring of asbestos fibres. This is supported by Regulation 20, which makes clear that employers undertaking their own asbestos air testing must carry it out in a way that satisfies the criteria as set out in ISO 17025.
Preparation for air sampling
Before analysis can be undertaken of a specific sample of air that may contain asbestos – including the calculation of the exact concentration of asbestos that may be present – it will be necessary to capture that sample in the first place.
When asbestos air testing and monitoring is required in a particular location or on a specific person, highly trained analysts typically attend with specialised equipment, which they use to take an air sample. The analysis of the sample that follows this – under the microscope – allows for an accurate calculation of the asbestos level to be made.
However, there are certain preparatory steps that will be required for air sampling. These include the selection of an appropriate location from which to take a sample, as well as the setup of specialised equipment such as air sampling pumps, sampling cassettes, and filters.
Great care will need to be taken, too, to ensure sample integrity, including the avoidance of contamination. A key aspect of this will be – if on-site analysis is not possible – the proper handling and transportation of samples to the laboratory.
Sampling volume and duration
Various factors will dictate the appropriate sampling volume when asbestos air testing is being undertaken in a property. These will include the expected concentration of asbestos in the air, as well as other environmental conditions.
The duration of sampling, too, will be important, with different sampling durations being recommended for different scenarios. Sampling procedures and strategies need to be designed where possible to provide sample densities within the range for optimal accuracy (100-650 f/mm2), or to ensure the minimum limit of quantification (LOQ) is based on at least 20 fibres.
Different types of air sampling are subject to different recommended flow rates, minimum volumes, and graticule areas to be examined. More details on these parameters can be found in the Health and Safety Executive (HSE)’s HSG248 document, entitled Asbestos: The Analysts’ Guide (Table 5.2, page 42).
Laboratory analysis and fibre counting
There are various laboratory analysis techniques that are commonly used on asbestos air samples. These include:
Phase contrast microscopy (PCM)
The standard method used for the sampling and counting of airborne fibres, PCM involves air being drawn at a known flow rate through a filter for a measured time. This results in particles being collected on the filter, which is subsequently mounted on a glass slide and rendered transparent to enable its examination under the microscope.
With this method, a known fraction of the filtered deposit is examined under at least 500x magnification. It is a quick and cost-effective way to identify airborne fibre concentrations. However, it also has the major disadvantage of being unable to distinguish between asbestos fibres and non-asbestos fibres.
Transmission electron microscopy (TEM)
The key difference between PCM and TEM is that the latter uses an expensive electron microscope to scan and identify the number of asbestos fibres present. Unlike PCM, TEM can tell the difference between asbestos and non-asbestos fibres, given that it scans for both morphology and elemental composition.
Scanning electron microscopy (SEM)
While PCM typically involves around 500x magnification when air samples are under microscopy examination, the SEM method allows for samples to be magnified up to 200,000x. Fibre counting is able to take place using SEM at 2000x.
Whereas PCM typically has a limit of detection of 0.01 f/cm3, for SEM, the limit of detection is 0.0005 f/cm3. This helps to make SEM the best technique for monitoring airborne levels of asbestos fibres in settings where asbestos-containing materials (ACMs) may release relatively low levels of fibres over a prolonged period.
Calculating asbestos fibre concentration
The basic formula for calculating fibre concentration, in terms of fibres per millilitre of air (f/ml), is as follows: the total number of fibres collected on the exposed area of the filter, divided by the volume of air sampled.
More detailed information on the fibre counting and calculation process is outlined in the relevant section of the HSG248 document under the heading, “Air sampling and analysis by phase contrast microscopy” (page 38).
This part of the guidance shows the following method for calculating the fibre concentration (C) in fibres per millilitre:
C = 1000 N D2 / V n d2
Where:
- N refers to the number of fibres counted;
- n is the number of graticule areas examined;
- D (mm) is the diameter of the exposed filter area;
- d (μm) is the diameter of the Walton-Beckett graticule;
- V (litres) is the volume of air sampled through the filter.
The initial step for calculating the fibre concentration in the sample will be the counting of the fibres on the filter. In the case of the PCM method, where at least 500x magnification is used, the analyst will examine a known fraction of the filtered deposit, and they will count the visible fibres in a known number of microscope graticule areas.
Interpreting results
Once the analyst has calculated the asbestos levels in the sample, they will need to compare this with the regulatory limits and guidelines. They will also need to consider what health implications the recorded concentration level could have for those who occupy or use the space where the air sample was captured.
Regulation 2 of CAR 2012 sets out a control limit for asbestos of 0.1 fibres per cubic centimetre (f/cm3). It should be noted that this is not a stark dividing line between a “safe” and “dangerous” concentration. However, if the concentration of asbestos fibres in a particular location is below this control limit, this would be regarded as “reasonably safe”.
As stipulated by CAR 2012, Regulation 19, records must be kept of the results of air monitoring. These results – or a suitable summary – must be kept for five years, except in cases where employees are under medical surveillance.
If the latter is the case for any of your organisation’s employees, such records, or a summary, must be kept to supplement the health records for 40 years.
Quality control and assurance in asbestos level calculation
To ensure the accuracy and reliability of the results from asbestos level calculation, it is crucial to have certain quality control and assurance procedures in place.
Such measures include taking the time and care to appropriately maintain and calibrate the specialist equipment needed for asbestos air sampling and analysis. Regular calibration schedules should be followed, alongside suitable maintenance measures for microscopes and sampling pumps.
Ensuring that the analysts who carry out asbestos air testing and analysis are well-trained and competent, will also be instrumental in making the most accurate calculations of airborne asbestos concentrations possible.
Indeed, Regulation 20 of CAR 2012 stipulates that employers must make sure that any person they engage to undertake asbestos air testing is not only competent, but also accredited by the appropriate certification body. This is supported by Regulation 21, which sets out the requirement for employers to make sure anyone they engage to carry out analysis is accredited to ISO standard by the appropriate body.
It isn’t merely the initial training an asbestos analyst receives that is crucial to ensuring their competence. Refresher training should also be provided at least once a year to any professional whose work regularly disturbs asbestos.
Further information on the exact training requirements for those could be at risk of disturbing asbestos during their work, is laid out in Regulation 10 of CAR 2012. The HSE’s L143 Approved Code of Practice (ACOP) document provides a guide to this.
Regulatory compliance and best practices
As we have already referenced in this piece, such stakeholders in the management of asbestos risks as building owners, employers, and asbestos analysts need to ensure they stay on the right side of the law, including with regard to the requirements outlined by CAR 2012.
Analysts can help ensure their own compliance with the regulations – and industry best practices – by following the aforementioned Analysts’ Guide under the HSG248 series code. This document can be downloaded in PDF format from the HSE website, and it sets out a range of specific guidelines. These include detailed protocols for sampling and analysis, as well as information on how asbestos levels can be calculated in line with industry standards.
Further best practices for ensuring continued legal compliance include carrying out regular audits and reviews, as well as being vigilant to keep up to date with any relevant regulatory changes.
Conclusion: the accurate calculation of airborne asbestos is utterly crucial
As we have sought to explore in this article, it is of critical importance – when asbestos air testing and air monitoring are being carried out – to ensure the airborne asbestos levels are accurately measured and calculated. After all, the information that emerges from this process will inform subsequent steps to manage the asbestos risks at the given location.
The accurate calculation of airborne asbestos levels, then, is vital for ensuring legal compliance and the safety of anyone who uses or occupies the specific site or building.
Our experts at Oracle Solutions would always urge business owners, duty managers, and other stakeholders in the management of asbestos to ensure all proper procedures are followed for asbestos calculation. To learn more about our own knowhow in asbestos air monitoring and air testing, and to receive a competitive quote, please contact our team now.
Written by Callum McDonald
Callum McDonald is an expert in asbestos quality management, ensuring rigorous adherence to regulations and high-quality standards in removal projects. His focus on enhancing quality and client satisfaction makes him a crucial asset in safety and compliance within the field. Callum's expertise in technical support and oversight of licensed works underscores his commitment to excellence in asbestos management, providing invaluable guidance to clients in this specialised area.