At 9.35pm on Wednesday (23) one crew from Huntingdon and one crew from Chatteris were called to a fire at the former RAF Upwood site.
Firefighters arrived to find an unattended bonfire in a derelict outbuilding and extinguished it using a hose reel. They returned to their station by 10.55pm.
The cause of the fire was deliberate. Anyone with information should contact police by visiting www.cambs.police.uk to submit an online report or call Crimestoppers on 0800 555111.