Crystalline silica, a common element found in many materials, can pose health risks when inhaled as fine particles. Accurately identifying its presence is crucial in proper risk assessment and management for a Crystalline Silica Process (CSP). Here’s how to test for crystalline silica in a substance:

Initial Screening:

Start by reviewing the Safety Data Sheet (SDS) of the material, focusing on Section 3 (composition). Look for mentions of quartz, cristobalite, or tridymite. If their combined proportions exceed 1%, the substance is considered a Crystalline Silica Substance (CSS). Section 8 may also indicate a silica risk if exposure standards are stated.

Not all materials may have a Safety Data Sheet (SDS), but other information such as geological petrographic analysis on natural stone material can be extremely useful. Solid materials may not have an SDS if they are not classified as hazardous substances in their current form. In such cases, bulk materials testing may be necessary to identify any crystalline silica to determine CSS status, even when SDSs are available.

There are two main reasons for determining crystalline silica content:

1. Bulk Crystalline Silica (CS) Testing is used to identify the potential hazard of silica in a material and assess whether a risk assessment is necessary.
2. Respirable Size Fraction in Bulk Material (e.g., SWeRF) is employed to determine the respirable size fraction in a powdered material before it is handled by workers. This assessment helps identify immediate risks associated with the material being transformed as part of a process.

Analytical techniques X-ray Diffraction (XRD):

XRD is the gold standard for identifying and quantifying crystalline silica. The process involves:

• Crushing the sample into a fine powder
• Exposing the powder to X-rays
• Measuring the diffracted X-rays with a detector
• Analysing the resulting diffraction pattern

Each crystalline structure has a unique “fingerprint” that can be matched against a database to identify the presence of crystalline silica polymorphs of α-quartz, cristobalite and tridymite. The intensity of XRD peaks provides information about the amount of silica present. Using an internal standard technique allows for accurate quantification.

Fourier Transform Infrared Spectroscopy (FTIR):

FTIR can be used in combination with XRD to resolve ambiguities, especially in materials with similar crystal patterns. It’s particularly useful for natural stone materials containing silicates.

Standardised Methods:

Draft ISO standard 6868 is in progress and is expected to be available soon. For reliable results, it is recommended that testing be conducted by a laboratory accredited by the National Association of Testing Authorities (NATA) or through the ILAC Mutual Recognition Arrangement (MRA).

Respirable Fraction Analysis:

For powdered materials, assess the respirable fraction using techniques like size-weighted relevant fine fraction (SWERV). This involves:

• Sedimenting the powder to isolate the respirable fraction
• Analysing particle size distribution
• Examining the isolated fraction using XRD or FTIR

Consider Material Transformation:

Remember that processing can alter silica content. Materials with non-crystalline silica may form into crystalline phases during heat or pressure treatment.

Avoid Misleading Techniques:

Instruments that only determine elemental composition should not be used to assess CSS, as they can’t distinguish between crystalline and amorphous forms.

Interpret Results Carefully:

A positive test (i.e., > 1 %) for crystalline silica doesn’t necessarily indicate immediate risk. Consider how the material is used and processed to assess potential exposure and the generation of respirable size fractions.

A positive test result for crystalline silica exceeding 1 % does not necessarily indicate an immediate risk. It is important to consider how the material is processed to evaluate potential exposure, the generation of respirable size fractions and identifying those workers who may be at risk if airborne particles are breathed in.

Ongoing Monitoring:

Regular testing may be necessary as part of quality control if processes or materials change.

By following these steps, you can accurately test for and quantify crystalline silica in substances, enabling the first step in proper risk assessment and management. Remember, the 1% threshold serves as an initial screening point – materials below this level generally don’t warrant further investigation for silica-specific risks, allowing focus on other potential safety hazards.