Why do I need to keep so much space between our stored materials and the ceiling?

For fire sprinklers to work properly, they must not be blocked in any way such that their spray pattern is impeded. There needs to be enough room for the spray from fire hoses to reach throughout the room. Any storage within 18” of sprinklered areas or 24” of non-sprinklered areas of the ceiling must remain clear, except when the storage is along a wall.