A white powder sent to a nuclear agency in Cumbria sparking an alert has turned out to be harmless, police said.
The suspect package was found by mailroom workers at the Nuclear Decommissioning Authority (NDA) in Whitehaven on Wednesday.
A cordon was set up by the emergency services while police officers took the substance away for laboratory tests.
But police have now confirmed the package contained a non-toxic, powder and are trying to trace the sender.
Fit and well
Cumbria Police said it was not revealing the identity of the powder in case it compromised the investigation.
At least 20 firefighters, along with police and two ambulance crews were on standby for more than five hours as the situation was assessed.
The NDA said it was reviewing security procedures as a result of the alert.
A spokesman said: "Three staff were isolated as a precaution and were reassured by ambulance staff. They are fit and well."
The NDA was set up two years ago to oversee the decommissioning of the UK's ageing nuclear facilities.