Had a thermal runaway in a Seaking around 1980 ish. It ripped a hole about 2 foot diameter out of the front end of the nose cone!
Damage came back as far as the tail rotor pedals.
Happened very quickly and in hindsight with only the whiff of a battery acid acrid smell.
My view now is to get the a/c down immediately, switch battery off, evacuate the a/c
