Normalisation of deviance is the process where what was unacceptable gradually becomes acceptable over time in the absence of failures. So, the longer a period without incidents, a requirement to wear a hard hat may start to be taken less seriously and later ignored. The unacceptable becomes the norm, no longer seen as deviant.
The term was used by Diane Vaughan when discussing the culture and events leading to the Challenger disaster. However, it’s easy to recognise it in much more mundane examples.
Classic workplace examples where deviance may start to become normalised include:
Normalisation of deviance can be particularly tricky to avoid when failures are rare yet severe or with known but distant dangers, such as smoking.