This from the BBC News report of the stupid balloon release.
Durham Police said officers decided to let the cars burn because "the field was contained and it was assessed there was no immediate risk to wider public safety".
County Durham and Darlington Fire and Rescue Service said one crew arrived at the scene but withdrew "given the circumstances and concerns for the safety of our firefighters".
Police said a majority of the crowd in the privately-owned field near Haswell had travelled from outside the County Durham area, bringing with them a number of vehicles.
The force said officers were called to the area shortly after 17:30 BST, adding that no-one was injured and no arrests were made.
A spokesperson for the fire service said: "Following a dynamic risk assessment, it was established that there was no immediate threat to public safety and no significant risk of the fire spreading.
"Given the circumstances and concerns for the safety of our firefighters, the decision was taken to withdraw from the area."