What might cause an explosive mixture according to guidelines about combustible dust?

The identification of mechanical failure of machinery as a potential cause of an explosive mixture is grounded in the understanding of how combustible dust behaves in an industrial setting. When machinery malfunctions, it can lead to unintended sparks or increased friction, both of which can ignite dust. Additionally, such failures may cause dust to accumulate in areas not intended for collection, further elevating the risk of explosion.

Normal operating conditions typically assume that equipment is functioning properly and safety mechanisms are in place, thus not inherently creating an explosive environment. Proper handling procedures are designed to mitigate risks associated with combustible dust, while the use of inert gasses is a protective measure meant to prevent ignition. Therefore, these options do not contribute to the creation of an explosive mixture in the way that mechanical failure does.