 Safety factors are numerical factors employed in the design process for our houses, bridges, vehicles, tools, etc., in order to ensure that our constructions are stronger than the bare minimum expected to be required for their functions. Elaborate systems of safety factors have been specified in norms and standards. A safety factor most commonly refers to the ratio between a measure of the maximal load not leading to a specified type of failure and a corresponding measure of the maximal expected load. It is common to make bridges and other constructions strong enough to withstand twice or three times the predicted maximal load. This means that a safety factor of two or three is employed.