A controlled explosion has been carried out at a Peterborough engineering works following the discovery of an "unstable chemical".
The incident took place at the Perkins engineering site in the city.
The building in Frank Perkins Way was evacuated while a bomb disposal team from RAF Wittering dealt with the plan.
Police say there was no risk to the public and the plant has now reopened.
"A controlled explosion has been carried out on the unstable chemical found at Perkins engines and that has negated any threat posed by it," Inspector Kieran Mylchreest, from Cambridgeshire Police, said.
Mr Mylchreest previously described any risk to the public as "very, very low", and said any previous safety advice has been lifted now the incident is over.