Physical hazards differ from hazards related to the toxicity of chemicals and materials in a number of ways. Their origin is the sudden and accidental release of chemicals and/ or energy - that is, chemical accidents, explosions, and spills - as distinct from the expected products, by-products, or gradual pollution associated with chemical production and use. The chemicals or materials are not always inherently toxic. For example, flour or olive oil can be explosive in an industrial operation if the particles or mist, respectively, are fine enough such that a spark leads to an ignition. Therefore, not only are the inherent characteristics of materials relevant, but also the processes associated with their production, use, or storage (for example, grain elevator explosions come to mind). More than substituting starting or feedstock materials - or making a different chemical - may be needed to prevent untoward events. Hence the design of both inherently safer materials and production systems must be addressed.