Originally Posted by bsieker
I'm not aware of any damage to nearby equipment. I agree with Machaca here that apparently the safety systems (or call it hazard mitigation) did their job.
First, I'm honored to have earned a comment from you.
But, second, I think the "no harm done" view voiced by some here is rather too optimistic. The electrolyte in these batteries is itself a hazardous substance. In particular, it is itself flammable (or inflammable in proper English before the insurance companies decided we would not figure out what that meant), corrosive, and conductive. Second, the very high energy production by a cell which reaches thermal runaway practically guarantees that electrolyte will exit at high temperature and high pressure.
While photos of the ANA battery case might suggest that just a little seepage occured at seams, multiple press accounts describe a more energetic event. Recent articles in the Wall Street Journal assert that both incidents included both leaking electrolyte and smoke damage to "nearby portions of the aircraft". An early Seattle Times story described this of the ANA incident:
Hot chemicals sprayed out of the battery on the 787 Dreamliner in this week’s emergency landing in Japan, leaving a gooey dark residue and suggesting a different malfunction than last week’s 787 battery fire in Boston, according to two people with knowledge of the situation.
The residue covered the battery and splattered over nearby instruments inside the forward electronics bay. It left a 12-foot-long dark streak from the battery to an outflow valve through which some of the spray vented overboard during the flight.
I don't think that outer battery case was designed to contain a full thermal runaway event without hazard to surroundings, and I don't think we'd want to see many repetitions to see whether we continue to be lucky with that particular hot fluid spraying about in an electronics bay.
My friend who has blown up a great many lithium ion batteries, in addition to more gentle means of assessing their behavior, does not think a pressure vessel for full containment is practical. His tests are on single cells tiny compared to these, in custom chambers capable past 3000 psi, and he has had chamber failures. Possibly if this is to be designed to fail safely to the degree of all-cell thermal runaway, the outer battery chamber needs to guide the inevitable electrolyte spray to a safe exit channel.