What percentage of rock dust is required in the return?

The correct answer is 80%, which is the standard percentage of rock dust required in the return airflow of a coal mine to help control the potential for coal dust explosions. Rock dust is an essential safety measure, as it helps to impede the combustion process of coal dust and reduces the overall flammability of the environment in the mine.

Implementing the appropriate percentage of rock dust is critical for maintaining safety standards and mitigating risks associated with dust explosions. The use of 80% ensures that there is a sufficient layer of non-combustible material to suppress ignition and provide an effective barrier against the flammable coal dust that may accumulate in the mine.

Understanding the significance of this percentage is crucial for mine safety practices and compliance with regulatory guidelines, which aim to protect workers and maintain safe operating conditions.