Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, a Factor of Safety (FoS) expresses the degree to which a system is reinforced to avoid failure at a given load. In order to have a Factor of Safety, a system must be able to have a determinable failure point as well as nominal load. For example, a steel walkway with a FoS of 4 means that it is designed to withstand quadruple the nominal load without breaking. Using a FoS may be a legal requirement in some industries, typically when the failure of a machine would cause loss of life or injury.