What concentrations must be monitored and recorded in the atmosphere of the work environment?

• A. Total dust concentration in the atmosphere
• B. Gas concentrations
• C. Concentrations of respirable dust and free silica in the atmosphere of the work environment
• D. Noise levels

Answer: (C)

The key idea is focusing on what inhalation hazards matter most in the atmosphere of a mining work area. In coal mining, the health risks come from the tiny particles that can penetrate deep into the lungs, especially the fraction small enough to be respirable. Those respirable dust particles, when they contain free crystalline silica, pose significant long‑term health dangers like silicosis. Therefore, the concentrations that must be monitored and recorded are the amount of respirable dust present in the air, and the amount of free silica within that respirable dust.

Monitoring total dust would overstate or understate the actual risk because larger particles don’t get deep into the lungs the way respirable particles do. Gas concentrations and noise levels are important in other contexts—gas monitoring for toxic or explosive gases, and noise monitoring for hearing protection—but they address different hazards rather than the particulate exposure described here. The emphasis in this scenario is on respirable dust and its silica content, as these are the specific atmospheric concentrations that drive the required health risk assessments and controls.