Homes were evacuated after a fire broke out at the atomic weapons base which maintains warheads for Trident, the country's nuclear deterrent.
Firefighters were called to a building in the non-nuclear explosives area of the Atomic Weapons Establishment (AWE) in Aldermaston, Berkshire, at about 9pm last night.
The AWE said there were "no radiological implications".
One member of staff received minor injuries and was treated by first aiders on the site.
An AWE spokesman said: "As a precautionary measure, a 600-metre cordon was set up around the building and a small number of local residents were evacuated overnight from their homes in the Red Lane area.
"A full investigation into the causes of the incident, which has no radiological implications, will be undertaken.
"The Ministry of Defence and AWE's regulators have been informed."
The AWE's own fire and rescue crews were supported by firefighters from the Royal Berkshire service.
A spokeswoman said six appliances from Berkshire assisted at the scene, maintaining a presence overnight.
AWE provides and maintains the warheads for Trident, the country's submarine-launched nuclear deterrent.
The company's headquarters at Aldermaston cover about 750 acres.