What should be ensured about the space behind line brattice?

The requirement for the space behind line brattice to be clean and open for free air flow is crucial for maintaining adequate ventilation within the mine. Proper airflow is essential for diluting and removing harmful gases and dust that can accumulate in the mining environment. A clear passage ensures that fresh air can circulate effectively, which is vital for the health and safety of the workers as well as for the operation of mining equipment.

If the space were cluttered with materials, as indicated in one of the choices, it could obstruct airflow and create dead spots where stale, contaminated air might linger. Similarly, sealing the space completely would also prevent necessary ventilation, leading to poor air quality. While filling the space with air-purifying agents might seem beneficial, it does not replace the fundamental need for unobstructed airflow, which is critical for overall mine safety and efficiency. Maintaining a clean and open space behind line brattice directly supports the operational standards for air quality management in underground mining.