When handling coal deliveries, the oxygen concentration must not exceed what percentage of free oxygen by volume?

The correct answer is based on safety standards concerning the handling of coal, where maintaining a specific level of oxygen concentration is crucial to prevent fire hazards. A maximum free oxygen concentration of 12 percent by volume is established to minimize the risk of spontaneous combustion. Coal, particularly when stored or transported, can pose a significant fire risk if oxygen levels are too high, as oxygen fuels combustion processes.

At concentrations above 12 percent, the likelihood of igniting coal dust or other particulates increases substantially, which can lead to dangerous situations such as fires or explosions in mining operations. Therefore, keeping the oxygen concentration at or below 12 percent serves as a critical safety measure in the coal handling process, protecting both equipment and personnel involved in these operations.