On April 18, the U.S. Department of Labor’s Mine Safety and Health Administration issued the final rule on Lowering Miners’ Exposure to Respirable Crystalline Silica and Improving Respiratory Protection, which lowers the permissible exposure limit of respirable crystalline silica to 50 micrograms per cubic meter of air for a full-shift exposure, calculated as an eight-hour, time-weighted average. If a miner’s exposure exceeds the limit, mine operators are required to take immediate corrective actions to come into compliance.