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Mechanism of Battery Failure

The mechanism of a battery failure which would send smoke into the cabin was examined by Boeing's project team, which was put together to develop a package of preventive measures.
The project team found that the battery failure that would send smoke into the cabin was triggered by the overheating of one of the 8 battery cells in the blue battery case, for some reason.

image:787 Battery787 BatterySource; Transport Safety Board

image:Internal Structure of BatteryStructure inside the battery

First, one cell overheated.

When a cell overheats, electrolyte fluid inside the cell vaporizes into white vapor (fumes), which is released outside the cell, and subsequently, the cell no longer functions.

Heat is transmitted to other cells and they also overheat.

The cell is designed so that it does not affect the other cells in the event of overheating. But in the battery failures that occurred, it was found that when one of the cells overheated and lost its function, it might have affected the other cells. For example, it might have short-circuited and transmitted large electric currents or heat to other cells. U.S. and Japan transportation investigative agencies have stated that overheating of one cell initially occurred in the battery failure.

image:Identified mechanism of battery failureMechanism of battery failure that was identified in the investigations

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