Answer: flaresup

AnswerCrossword Clue
FLARESUP

Suddenly intensifies

FLARESUP

Catches fire

FLARESUP

Bursts into flames

FLARESUP
Gets angry
FLARESUP
Flies off the handle.
FLARESUPFlies off the handle
FLARESUPComes back, in a way
FLARESUPIntensifies