What are the Dangers?
The Ministry Of Defence (MOD) says there is little risk of a nuclear detonation during transport, but in an accident the highly volatile “conventional” explosive could be set off, causing the warhead to ‘jet’ plutonium. It estimates that, in a serious accident a circle some 600 yards in radius would be affected by blast and fragments of explosives. Even more problematic than the explosion itself would be its effect in dispersing alpha emitting plutonium and uranium particles down wind for miles. Alpha particles emitted by plutonium are not a serious risk if they remain outside the body, but if particles are ingested or inhaled they can cause cancer.
Nuclear weapons convoys often pass close to or even through large towns. It would be impossible to evacuate heavily populated areas on the routes in time to avoid the potential consequences of a traffic accident involving a nuclear warhead. MOD accident guidelines do not explain whether traffic would be quarantined, sent on its way or gridlocked in the contaminated zone.
Nuclear weapons convoys and Local Authorities
Local Authority Emergency Planning Officers have been given guidance (the Local Authority & Emergency Services Information) about how to respond to any emergency arising from the passage of convoys. Local police are informed when a convoy is due to pass through their area, but not Fire Brigades.
1. But see revelations about the possibility of an "inadvertent yield" http://www.robedwards.com/2006/07/road_crash_coul.html