All materials stored in tiers must be secured to prevent what?

The storage of materials in tiers must be secured primarily to prevent multiple hazards, making "All of these" the correct choice. When materials are stacked or stored in tiers, there is a risk of sliding, which can cause items to become unstable and potentially tumble off their shelves or supports. Falling is another critical concern, as unsecured materials may drop from their stacked positions, posing a danger to personnel and the surrounding environment. Collapse refers to the structural integrity of the tiered storage itself; without proper securing measures, the entire stack could give way under its own weight or due to external forces, leading to a catastrophic failure.

Securing materials effectively reduces the risks associated with these potential failures, enhancing safety in the work environment. In essence, tiers of materials must be managed with stability in mind to prevent any of these dangers, which is why all three - sliding, falling, and collapse - are valid considerations in storage practices.