My bike is ticking...

[Dead Eye]

:eek Sorry to hear and see the aftermath of this.

I expect the sparks from the electric motor on your home made ultrasonic bath ignited petrol fumes.

Think of this as a challenge for a winter project  :rolleyes or not...

Its a fair guess and may be right - but there was no smell of fuel and no rags / containers nearby that had been subjected to fuel / flammable liquids (that weren't sealed - there was a can of Carb Cleaner that I'd just bought on the dryer - the bath was on the floor). I'd used the bath the day before for over an hour and a half and there were none of the smells for electrical burnout and no excessive heat on the sander or box... Obviously it was the sander that started it, but how is a complete mystery to me at current.