Broadly defined, bulk solids are a mixture of discrete particles, handled in various quantities. Examples include plastic pellets, salt crystals and fine powders. A material’s properties, such as particle size, moisture content and chemical composition, vary widely, introducing unique process-safety challenges that require careful consideration of the handling methods. Safety issues often arise simply from misunderstanding how bulk solids behave. For example, it is common for process engineers to treat silos like liquid tanks, but bulk solids generate complex frictional forces, both among particles and against the containing walls, creating unpredictable flow behaviors and often misconstrued load distributions. If these effects are ignored during design, structural failure is a common result.