If you are a supplier or manufacturer, it is an obligation to ensure safe working conditions for employees and safe-to-use products for consumers. Companies dealing with monitoring and control of respirable silica and asbestos are government agencies involved with environmental monitoring, mine sites, cement plants, product manufacturing including construction, paint, paper, insulation, vehicle parts, cosmetics and more. 

To learn more about the related health risks and possible exposure points to respirable silica and asbestos read our blog article here.

Always wanted to know which analytical technique is more suitable for quantification of crystalline hazardous substances like respirable silica and asbestos?

To gain a better general understanding of the materials characterization methodologies watch the on-demand webinar presented by Nicholas Norberg. He discusses methods like infrared spectroscopy (IR) and X-ray diffraction (XRD) in the context of stringent monitoring of low quantity respirable silica and asbestos. He provides insight regarding the plus points and limitations for the identification, quantification, and adherence to the existing norms.

Many questions were asked during and after the webinar, which are listed below, along with answers for your interest. If you have any further questions, please don’t hesitate to contact Nicholas directly here.

Where can we get the reference standard materials you have used to carry out calibration curves?

The asbestos standards were made for us by a Lab in the UK which was organized by one of my colleagues. I was not involved in the acquisition process. Therefore, unfortunately, I cannot provide you with a contact. The RCS standards were user samples, prepared according to MDHS 101 method. There are several published methods describing sample preparation procedure in detail, e.g. NIOSH 7500 and MDHS 101 for the preparation of respirable silica standards; NIOSH 9000 for the preparation of asbestos on filter samples.

In your calibration curves the Y-axis is referenced as mg/m3. How can you get it?

Usually, the values of reference filters are mentioned in mg, therefore I assumed that these values referred to the mg/m3 that are mentioned in regulations but that, of course, depends on how the real air filter samples are collected. But if e.g. asbestos is extracted from a matrix (e.g. cement) then it should only be mg. Therefore, probably writing mg on the graphs would have been more correct.

How do you differentiate tremolite from lizardite? One is amphibole and the second one is not, but both of them appear (the intensity peak) at the same angle.

The major tremolite peak and the main Lizardite peak do not appear at the same angle. Lizardite is a serpentine and therefore the main peak appears at ca. 12.1 deg 2theta similar to chrysotile. The main tremolite peak (same as all amphiboles) have their strongest peak around 10.6 deg 2theta. This is described on slide 26 in my presentation where the difference between amphibole and serpentine peaks is discussed. The given angular positions refer to Cu-radiation.

Coesite, is considered a SiO2 polymorph? How do you quantify it?

Same as quartz, only using the characteristic peak positions for coesite. However, coesite and stishovite are high-pressure polymorphs of SiO2, therefore they are very rare and hence not mentioned in the Norms.

What is the best reference standard material to carry out the calibration curves for the RCS quantification?

To the best of my knowledge, it is not possible to purchase ready RCS standards for XRD quantification. All laboratories dealing with RCS quantification, prepare standards internally, following one of the existing methods (e.g. MDHS 101, NIOSH 7500).

Asbestos calibration curves (with talc) show some different mixtures. How those mixtures were made to ensure that the microstructure (fiber shape) is not destroyed? Using a mortar or a mill? How do you evaluate that the fibers have not been modified?

These mixtures were mixed and prepared in mortars. For the XRD measurements, the fiber shape does not significantly affect the diffraction signal (intensities and position).

Would you like to learn more about the Malvern Panalytical solution for respirable silica and asbestos or to try-out the solution on your own samples? – contact your local Malvern Panalytical representative to arrange a demo.