Methods for measuring asbestos fibres in the air

1.1.       What is Asbestos air monitoring?

The aim of asbestos air monitoring is to assess exposure and the effectiveness of control measures by measuring the number of respirable asbestos fibres in the air. This is generally undertaken where asbestos-containing products are in poor condition, potentially liberating asbestos fibres into the air, or where asbestos-containing materials are being removed.

For the purposes of asbestos air monitoring, only respirable asbestos fibres (those fibres less than 3 μm wide, more than 5 μm long and with a length-to-width ratio of more than 3 to 1) are considered to be a risk.

1.2.       What types of tests can be conducted to measure the asbestos fibres in the air?

Asbestos fibres in the air are generally tested by one of the following two methods:

  • PCM (Phase Contrast Microscopy)
  • TEM (Transmission Electron Microscopy)

However, many other types of tests can be carried out and should be understood. Their characteristics should therefore be thoroughly understood before deciding which of them is to be used for measuring asbestos in the air at a jobsite or elsewhere. In this regard, the table below briefly describes what each of these tests consists of.

TESTS CONDUCTED TO MEASURE ASBESTOS IN THE AIR
1PCM

(Phase Contrast Microscopy)

 

  • A pump is used to draw an air sample through a filter, then a slice of the filter is taken and examined it under a microscope for evidence of fibres.
  • This method measures only the total number of fibres in the air and does not differentiate between asbestos and other types of fibres.
  • PCM testing does not measure the smallest fibres and can miss significant asbestos hazards.
  • The process is quick and inexpensive.
  • This testing should only be performed when knowing that there exists an asbestos hazard and want to roughly quantify how much is present.
2XRD

(X-ray Diffractometry)

  • This method consists of a comparative technique based on the fact that each crystalline body presents a specific response to X-rays, which is reflected in a diffractogram that will present certain peaks.
  • The comparison comes when these diffractograms are taken and compared with other diffractograms collected from specific databases. This allows the composition of the sample to be accurately identified.
  • It is a useful screening test.
  • For a good result in an XRD analysis, it is essential that the compound is present in a certain concentration.
  • As asbestos minerals are fibrous, they are difficult to crush, which is necessary to prepare the sample, so their response to XRD is not very strong.
  • Usually, asbestos minerals are found in combination with other materials, which must be removed to focus the technique on the asbestos minerals.
3XRF

(X-ray Fluorescence)

  • The X-ray Fluorescence method identifies elements that are present to aid in XRD profile matching.
  • It rules out certain asbestos types if some minerals are not present (e.g. absence of Ca, cannot be tremolite).
  • This method cannot differentiate between asbestos in form and cannot determine the varieties.
  • It gives a semi-quantitative identification of elements.
4PLM

(Polarised Light Microscopy)

  • By utilizing the polarized light microscope, analysts test the optical properties of the samples’ fibrous components and provide both the asbestos type and estimated percentages in the sample material.
  • It is a simple cost-effective analysis.
  • It is an accepted method for the initial analysis of bulk building materials for asbestos content.
5SEM

(Scanning Electron Microscopy)

 

or

 

MEB

(for its acronym in different languages)

 

  • This technique uses an electron beam to examine the surface of the sample in great detail.
  • It provides several advantages, such as the possibility of zooming and fine detail. Analysis through using Scanning Electron Microscopy (SEM) enables magnification of samples of up to 200,000x, with fibre counting at 2000x, in comparison to 500x magnification when using a Phase Contrast Optical Microscope (PCOM or PCM) method.
  • This method also allows energy-dispersive X-ray microanalysis (EDAX) to determine the composition of the material and to make an exact measurement of the length of the fibres of which it is composed.
  •  It is particularly useful for identifying asbestos fibres due to its high resolution.
  • This method determines the morphology of the material.
  • It allows a 3D view of the particle.

 

6TEM

(Transmission Electron Microscopy)

 

 

  • Air samples are sent to a laboratory where the air sample is bombarded with electrons inside a giant electron microscope.
  • This is a method that captures even very fine fibres and reports only on those that are asbestos fibres.
  • TEM is more expensive and takes longer than PCM.
  • This method allows to truly assess the hazards that may be present due to asbestos fibres in the air.
  • The inconvenience of this method is that it only allows a 2D view of the particles and not in 3D.

1.3.        Which tests are commonly performed in the different countries of the EU?

There are a total of 50 countries in Europe, 27 of which belong to the European Union. A full analysis of how airborne asbestos fibre measurements are being conducted in detail in each of these countries is therefore unfeasible in this document.

However, to give a general insight into the current situation in Europe in this respect, some examples of what tests are being used in various countries are given below.

EXAMPLES OF TESTS USED IN DIFFERENT EUROPEAN COUNTRIES TO MEASURE ASBESTOS FIBRES IN THE AIR
NetherlandsPCM method is the most commonly used. Although it depends on the type of fibre, if it is expected (or known for certain) that the asbestos present is of the more hazardous types, mainly crocidolite, then the TEM method is used.
United KingdomThe TEM method is widely implemented in the UK. They consider it easy to use and much more reliable than other methods, so it is the method they use in almost all situations.
SwedenThe use of the PCM method predominates. Since TEM has not yet been widely implemented, they are not yet used to it, which makes it perceived as a complex method, leaving its use, therefore, relegated to exceptional situations that require very precise information to be obtained.
FinlandIn Finland, they use the SEM method for almost all measurements. The laboratories are very well prepared to conduct these tests and are the ones that are requested and performed.
BelgiumThe use of the PCM method predominates. The TEM is only employed to clarify the situation when there are doubts about the type of fibre being observed. For example, cotton fibres look very similar to asbestos fibres, so it is sometimes necessary to use greater precision (TEM) to distinguish the two.
FranceFor measurements of asbestos fibres in air they only use the TEM method. In 2015 national asbestos regulations were modified and the exposure limits were lowered significantly, requiring the most accurate methods to be used to ensure that the thresholds were met.
SlovakiaThe predominant method used in Slovakia to measure asbestos fibres in the air is the TEM.
SpainThe predominant method used is PCM. The TEM is only used for contrast and clarification in case of doubt.

1.4.       What is the impact of the new asbestos EU Directive on asbestos air monitoring?

The new asbestos Directive implies many changes in the asbestos decontamination sector at the European level. However, these changes will not affect all EU Member States in the same way, as the level of development of asbestos protection policies differs widely from country to country.

Regarding the measuring of asbestos fibres in the air, the new Directive states – in section 6c – that “fibre counting shall be carried out by electron microscopy or by any alternative method that provides equivalent or more accurate results”.

In addition, from 2029 it sets two different thresholds to apply, depending on the type of fibres considered when determining the measured value. In summary, these can be defined as 0.01 fibres/cm3 for measurements that consider even the smallest fibres, or 0.002 fibres/cm3 for measurements that leave out the smallest fibres, as with some methods they cannot be detected.

Overall, although not explicitly stated in the directive, this means that the wider limit of 0.01 fibres/cm3 from 2029 onwards can only be applied if measurements are made using the TEM methods. If other methods are used, since they are less precise, the limit will be further reduced to 0.002 fibres/cm3.

This leads to the use of the TEM methods to measure the number of asbestos fibres in the air.

In this regard, as can be read above, some countries already have well implemented the use of the TEM, just as the Directive indicates it must be done. However, several others still use the PCM more commonly.

TEM air sampling is the superior method due to its precision and accuracy. However, PCM has its value as far as being able to index exposure and its lower cost.

This poses two challenges for countries that do not yet have TEM implemented as a predominant method. On the one hand, they will have to start having more laboratories and specialists available to carry out these measurements, as the demand for them will start to increase significantly.

On the other hand, they will have to allocate more budget to carry out these tests, as TEM is more expensive than PCM.

However, they still have until 2029 (5 years from now) to prepare to implement these changes, so the transition can be done slowly, and therefore should not be considered a major problem.

1.5.       What methods or strategies can be followed to perform asbestos air monitoring?

Regardless of which test is performed (PCM, TEM, etc.), there are different methods or strategies for measuring asbestos fibres in the air, whose use will depend on the particular needs of the situation or project.

The following table describes the different types of approaches to performing asbestos air monitoring (it should be noted that in different regions each of the methods may be named differently, although in the end, the approaches remain essentially the same).

STRATEGIES FOR MONITORING ASBESTOS FIBRES IN THE AIR
1Asbestos reassurance air testing and monitoring
  • Reassurance air testing is often used when people are concerned that asbestos has been disturbed and there may be a risk of asbestos exposure. This is an unplanned asbestos disturbance.
  • The air testing confirms the amount of asbestos fibre that is airborne and provides details on the likelihood of any asbestos exposure to those that have been or will be near the affected area.
2Control asbestos air test and monitoring
  • These control air tests and monitoring are used when to monitor the asbestos in-air quantity during asbestos remediation or asbestos removal works.
  • The air testing is carried out in the background when the asbestos task is being carried out.
  • From the results of these controls, it can very quickly be determined if the works being undertaken are being carried out safely and that the control measures being employed are adequate to keep airborne asbestos fibre below any concentrations likely to cause asbestos-related health issues.
3Asbestos leakage air testing and monitoring
  • Usually, asbestos removal or remediation works are carried out in an enclosed area that, if built correctly, will have an asbestos-designed management system. This air management system places the asbestos enclosure under negative pressure. When the asbestos enclosure is compromised, the air is drawn into it and not released into the surroundings, thereby leading to asbestos exposure.
  • The asbestos air testing is carried out around the perimeter of the enclosed asbestos workspace and is designed to monitor the air for asbestos fibres. This would indicate if the enclosure has failed, resulting in the release of airborne asbestos fibres.

 

4Asbestos clearance air testing and monitoring
  • Asbestos clearance air testing and monitoring tests the air to measure the level of airborne asbestos fibres in an area following work or removal of asbestos-containing materials.
  • An area will be considered ‘cleared’ when the level of airborne asbestos fibres is measured as being below the threshold established by law, which considerably differs from one region to another.
5Personal air testing and monitoring
  • Personal asbestos air testing is specifically designed to test the air that the testing equipment wearer is likely to breathe in and be exposed to.
  • The purpose of these tests is to test the levels of respirable asbestos fibre for a particular person undertaking a specific task or set of tasks.
  • Additionally, personal air monitoring can be undertaken on an individual who is undertaking full asbestos removal or remediation work and is wearing appropriate respiratory protective equipment (RPE). The personal air testing results can then be reviewed to confirm that the RPE being used is adequate given the control measures in place and the amount of asbestos fibre being released into the air.
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