Why XRD Is the Smart Choice for MSHA’s New Silica Standard

Respirable crystalline silica (RCS) is one of the most significant occupational hazards in mining. With MSHA’s recent final rule lowering permissible exposure limits (PEL) to 50 µg/m³ (8-h TWA) and introducing an action level of 25 µg/m³, mine operators must now adopt more precise monitoring and analytical strategies.

The analytical method chosen can make or break compliance. At Eurofins Built Environmental Testing in Richmond, VA, we specialize in X-ray diffraction (XRD) using NIOSH 7500 — the gold standard for crystalline silica analysis — to ensure mining companies meet the new MSHA requirements with confidence.

MSHA’s New Final Rule: What Changed

• PEL lowered to 50 µg/m³ (8-h TWA) for all mines (coal and metal/nonmetal).
• Action level of 25 µg/m³ triggers exposure monitoring and corrective measures.
• Requires use of ISO/IEC 17025-accredited laboratories with validated methods.
• ISO 7708:1995-compliant samplers must be used for respirable fraction collection.

These changes make laboratory accuracy and defensibility critical for compliance.

Analytical Methods for RCS: IR vs. XRD

Two main laboratory techniques are commonly used:

• Infrared Spectroscopy (IR / FTIR) — NIOSH 7602, 7603, MSHA P-7
• X-Ray Diffraction (XRD) — NIOSH 7500 (method run at Eurofins Richmond)

Head-to-Head: IR vs. XRD

Infrared (IR / FTIR)

Pros:

• Lower cost and simpler instrumentation
• Fast turnaround for some sample types

Cons:

• Interference susceptibility: IR can suffer spectral interferences from mineral matrices (e.g. silicates, clay, feldspars, kaolin, or other oxides) that absorb in overlapping regions, causing baseline shifts or peak overlap.
• Limited polymorph discrimination: IR generally quantifies α‑quartz; it cannot reliably distinguish between quartz, cristobalite, and tridymite.
• Biased high results due to amorphous silica: Amorphous silica is common in mining samples, and IR cannot differentiate it from crystalline forms, leading to artificially elevated results.

X-Ray Diffraction (XRD) – NIOSH 7500

Pros:

• High specificity — distinguishes crystalline silica polymorphs (quartz, cristobalite, tridymite).
• Resistant to interferences — not affected by amorphous silica and complex mineral matrices.
• Defensible results — provides clearer evidence in regulatory or legal contexts.
• Approved for both coal and MNM dust — making it the most versatile and compliant method.
• Sensitive at low levels — supports accurate quantitation down to and below MSHA’s new action level.

Cons:

• Higher equipment and operational costs
• Longer analysis time compared to IR

Why XRD is the Better Choice for Mining

For mining companies, dust samples often contain amorphous silica and complex mineral mixtures. These conditions make IR less reliable and prone to bias. By contrast, XRD (NIOSH 7500):

1. Provides accurate results in mixed mineral matrices.
2. Avoids false positives from amorphous silica.
3. Meets MSHA’s approved method requirements for both coal and MNM operations.
4. Produces results with the legal and scientific defensibility needed under the new standard.

Eurofins Built Environmental Testing: Your Partner in Compliance

At Eurofins Built Environmental Testing in Richmond, VA, we are fully equipped to support mining companies under MSHA’s new silica rule:

• Accredited to ISO/IEC 17025
• Specialized in XRD analysis using NIOSH 7500
• Optimized for low-level detection, polymorph differentiation, and interference control
• Fast, reliable turnaround with QA/QC protocols ensuring accuracy
• Clear reporting that integrates seamlessly into MSHA compliance documentation

With our dedicated expertise in mining environments, we are ready to help your operation reduce risk and stay ahead of regulatory deadlines.

As MSHA enforces stricter silica exposure limits, laboratories must deliver reliable, interference-free results. While IR may seem faster, it is prone to false highs due to amorphous silica — a common issue in mining samples. XRD using NIOSH 7500 is the clear choice for accurate, defensible compliance testing.

Contact Eurofins Built Environmental Testing in Richmond, VA today to discuss your silica monitoring program, request a quote, or schedule sample submissions. Ensure your mine is ready to meet MSHA’s new exposure standard with confidence.