Miners were running on 490/1480.
Wow you pushed it too far? Default is 350/1200, too many Gigawatts!
Might want to try adding a fan to the other side of the board if you're running them hot.
The pieces of card are normal. I have them on my first Hex16B. I think they were there to stop some solder shorting on the heatsink. Did you remove the card before it blew up?