I had a near miss (or near hit?) involving lithium ions October last year:
I wanted to get the tail cap current of my Sky Ray King using 4 x Sanyo UR18650FMs rated at 2600 mAh but I could not remove the PCB in its bottom part (damaged screws) so I tried in improvise by using a copper plate to connect the four positive ends of the 18650s and use it and the flashlight body to connect it with the head of the light and my DMM to get the readings.
While doing it, the metal connecting the positive ends accidentally got in contact with the body. The SRK body instantly became very hot that I dropped it to the floor (good it was made of wooden tiles) and in the process disconnecting the circuit. No the Sanyo Lithium Ions did not explode or vent but the SRK springs connecting the negative end of the batteries melted and the wires and the copper plate were ‘welded’ into each other. Good thing (I guess) that copper and aluminum is not easy to weld and the shock of the drop was enough to cut the circuit. Otherwise the results could have been worse.
The Sanyos survived the near miss and they are still up and running. With my recent acquisition of the Opus C3100 through our group buy, their average capacity readings is 2394 mAh.