Fire support teams were initially not allowed into an atomic weapons plant during a fire in a bunker containing explosives, it has emerged.
The BBC has learned a solvent used in manufacturing is thought to have caught alight at Aldermaston's Atomic Weapons Establishment (AWE) on 3 August.
The incident log showed support crews from Hampshire were delayed from entering until an escort was arranged.
AWE said it followed safety procedures and took "extremely prompt" action.
The plant provides and maintains warheads for the submarine-launched nuclear deterrent.
One person was hurt in the fire which burnt out after about four hours.
Berkshire Fire Service has said access to the site was a not as "smooth" as it would have liked.
The incident log was released after a Freedom of Information request from Nuclear Information Service (NIS), a group set up to foster debate on nuclear disarmament.
It showed that the fire control room first heard about possible explosives when an operator overheard a radio broadcast between AWE staff, but when asked, was told there was no other details available.
AWE said firefighters were briefed about the explosives on site rather than through the control room.
In a letter seen by the BBC, defence minister Peter Luff MP said early indications showed the fire started when the solvent methyl ethyl ketone, used in manufacturing, "flashed and caught light".
Peter Burt, from the NIS in Reading, said: "The incident log makes fascinating reading and tells quite a scary story.
"Firstly when some of the firefighters turned up they were kept waiting at gates because security staff wouldn't allow them access.
"Cover available for the rest of Berkshire was also very low because so many fire appliances were used to fight the fire at AWE. Only one was left to cover the whole of Reading."
Support fire vehicles from Hampshire, including a Land Rover, were initially refused entry to the site before an escort was arranged.
Olaf Baars, deputy chief officer for Berkshire fire service, said: "I've got to say the entry to the site was not as smooth as we would have liked, but most of that related to relief appliances.
"But we understand they cannot give us unrestricted access to the site; we need to be escorted to the area where needed.
"We dropped to one pump in the Reading area but it was supported by other appliances around the edge of Reading."
In a statement AWE said it took quick action to deal with the incident and followed standard procedures.
Staff notified the fire service of the fire within two minutes of discovery and called them to attend 15 minutes later.
AWE added: "On arrival [the fire service] took the primary operational role after being fully briefed on the situation, including the involvement of explosives.
"The fire was relatively small, confined to a single process building and was out within four hours."
AWE said an investigation into the cause is under way which will be made public, while a separate inquiry by the Health and Safety Executive is also being carried out.