factor of safety vs safety factor

factor of safety and safety factor both are nouns.

Word	Noun	Adjective	Verb	Adverb
factor of safety	Yes	No	No	No
safety factor	Yes	No	No	No

As nouns, factor of safety and safety factor are synonyms defined as:

factor of safety and safety factor: the ratio of the breaking stress of a structure to the estimated maximum stress in ordinary use

factor of safety (noun)	safety factor (noun)
the ratio of the breaking stress of a structure to the estimated maximum stress in ordinary use	the ratio of the breaking stress of a structure to the estimated maximum stress in ordinary use