I've just changed a failed LED 7W GU10 lamp that had been in an outside light. I took the cover off and found a rather interesting burn mark around the negative track.
Each LED device is three LEDs in series (glow at 7 V, 10 mA gives 9.3 V) so the total voltage would have been around 65 to 70 V when running normally.
The board is an aluminium one. The supply voltage is 240 V, 50 Hz. I assume that the voltage available if the LEDs go open circuit is quite big.
I'd never seen a burn mark like that on a board. It seems to be a failure of the insulation between the conductors and the aluminium board.