What is a principal requirement for permanent stoppings in mining?

The principal requirement for permanent stoppings in mining is that they should be airtight. This is crucial for mine safety and ventilation control. Airtight stoppings help to contain potentially harmful gases and dust within specific areas of the mine, which is essential for maintaining breathable air in active working areas and for controlling the spread of fires or other hazardous situations.

Moreover, airtight stoppings are designed to enhance air quality and ensure an adequate supply of fresh air to the work areas. By preventing air leaks, these stoppings maintain the integrity of the ventilation system, ensuring that air flows are as intended and can effectively dilute or remove contaminants.

In contrast, other options like using wood for construction, being temporary, or easily dismantled would not align with the primary goal of creating a stable and secure environment within the mine, which is vital for the health and safety of all workers involved in mining operations.