Air Sampling Programs: Asbestos Dust Hazard Evaluation

Read the U.S. Department of Labor (DOL) and the Mine Safety and Health Administration (MSHA) report about the health hazards from mineral dust inhalation. Miners are routinely exposed to carcinogenic dusts such as asbestos.

Evaluating the Hazard: Quartz, cristobalite, and tridymite are three forms of crystalline (free) silica; quartz, however, is the most common.

Cristobalite and tridymite have a different crystalline structure than quartz and are generally considered to be more harmful biologically.

Cristobalite and tridymite are thermally altered forms of quartz. They may be present in areas where substances containing quartz are heated, such as in refractories, sintering, calcining, or heat expansion.

Because these two substances are not detected in routine quartz analysis, mine operators should request a special analysis for cristobalite or tridymite if either of these silica materials are suspected to be present in the dust.

The Threshold Limit Value® (TLV®) for silica-bearing dust is dependent upon the amount (percentage) of free silica present in the dust. The TLV® for silica-bearing dust decreases as the percentage of free silica increases.

Whenever the dust composition includes two or more hazardous substances which affect the same organ or body system, the combined effect (additive) must be given primary consideration.

If the dust composition includes two or more hazardous substances that do not have the same biological effect, the TLV® for that dust will be the most restrictive TLV® of the constituents.

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