If constructed of wood, ventilation doors shall be covered with what kind of material?

When ventilation doors are constructed of wood, they must be covered with fire retardant material. This is essential for enhancing the safety of underground mining operations, as fire hazards can pose significant risks in these environments.

Fire retardant materials are designed to slow down the spread of flames and reduce smoke production, providing crucial additional safety measures. These materials can help protect the wooden structure of the ventilation doors from ignition and potential damage in the event of a fire.

Using fire-resistant or fire-retardant coverings ensures a balance between maintaining ventilation functionality and adhering to safety standards in mining operations. The options involving metal sheathing or waterproof material do not specifically address the fire safety aspects required for wooden ventilation doors. Thus, fire retardant material is the most appropriate choice for ensuring safety and compliance in the mining industry.