This article was reproduced with the kind permission
of the British Broadcasting Corporation
30 November 2007, 17:59 GMT
Police said hay bales inside the outbuilding on Pattenden Lane, Marden, near Maidstone, were set alight at just after 2000 GMT on Tuesday.
Fire and electrical equipment being held in a nearby lorry was also damaged by the blaze.
Insp Ian Sandwell has urged land owners and people with barns in east Kent to watch out for any suspicious activity.
He added: "Although this may have just been an act of mindless violence, it caused extensive damage and without the quick actions of both police and fire officers the outcome could have been far more severe."
Stuart Skilton, of Kent Fire and Rescue Service, said: "We want to get the message out that arson is a crime, not just harmless fun, and deliberate fires are destructive and dangerous.
"It can be a matter of life and death. Fire setters are putting themselves, and others, at serious risk.
"They have the potential to divert valuable fire-fighting resources away from other incidents such as house fires or road traffic collisions where lives may be in danger."