Engine start.. grass fire near miss

After repeated attempts to prop swing start a FW44 biplane fuel was dripping on to the grass below. When the engine finally did start a flame from the exhaust ignited the fuel vapours below. The pilot was not aware of the fire and the prop swinger shouted for help. Luckily one of the watching air display spectators was an airframe fitter and grabbed an extinguisher and helped the prop swinger get the fire out.

My question is why are fire crews not watching the engine starts at such a small venue as Old Warden? And if there is a fuel spill why not push the aircraft back a bit before further attempts to start?