Why must caution be exercised to prevent grease from mixing with oxygen?

Grease is often flammable and poses a significant fire hazard when mixed with oxygen, particularly in an underground mining environment where there may be sources of ignition. When grease is exposed to high temperatures or open flames, it can ignite and lead to dangerous fires or explosions. This risk is amplified because the presence of oxygen increases the potential for fire, making it crucial to maintain proper handling and storage methods to avoid any situation where grease could come into contact with oxygen.

Understanding this hazard is essential for ensuring the safety of rescue operations and minimizing risks in mining activities. The other options address issues like corrosion or efficiency, which, while relevant in other contexts, do not highlight the immediate fire and explosion risks posed by a mixture of grease and oxygen.