Syseng68k
Abrasion, loose terminals, crimps or other electrical problem generating
enough heat to cause a fire. I think that's a much more likely scenario, as the
energy density required to set light to the composite would be quite high
(otherwise it has no business being used in a transport a/c) and need to be
sustained for some time to cause what is reported to be major damage, enough
to scorch the outer skin. What materials sustained the fire, once started ?.
The elt batteries are not in that class really, but ok, if we suspend critical
facilities for a moment, what was adjacent to the elt to spread / aggravate
a minor fire into a fairly major one ?. Does anyone have links to a pic of the
elt installation in the a/c, or just a pic of the internals around that area ?.
Would be very helpful to have that...
While everyone is hypothesising.... take the report from Ancient Mariner about a "
small battery, probably 1/3 of the size on an IPERB/ELB" so scale it up to a much larger battery and put that battery in a strong metal container that has its hermetic seal compromised by crushed power wire(s). The repeated heat from the sun on a hot day expands the metal box and eventually the compromised insulation allows a short while the same heat has already taken the battery to critical temperature. The energy release is inside a hermetically sealed box with the exception of the break caused by the same crushed wire(s). All the exothermic energy that led to Ancient Mariner's battery flying around the room is now focused in a jet through the break in the hermetic seal of the ELT. Effectively the ELT could become a self fuelling blow torch anchored to the crown of the fuselage as the battery goes into thermal runaway.
From
Battery fires: keeping the Li-ion caged | Aviation International News
"Thermal runaway can occur when the battery self-heats, which can happen when electrolyte reaches temperatures as low as 158 to 194 degrees F (70 to 90 degrees C), according to the FPRF report. Runaway accelerates quickly at higher temperatures, and the greater the charge in the battery, the faster runaway happens. Temperatures during a runaway can reach 1,110 degrees F (600 degrees C). The battery cells will also experience increased pressure, venting or popping of the cell, possible ignition of cell gases, possible ejection of cell contents and propagation to adjacent cells.According to the FPRF report,
“Venting of isolated small cells (cellphone cells and smaller) seldom results in flame ignition. This is likely due to the limited volumes of vent gases released from these cells–that is, the gases become diluted before ignition can occur. In comparison, ignition of vent gases from 18650 and larger cells [used in some laptops] is fairly common: these cells contain more electrolyte (more fuel), and are usually used in multi-cell battery packs. If the flow of vent gases is ‘restricted’ due to the configuration of a vent port (typical in hard case cells), flames emanating from the cell will be highly directional (flames from 18650 cells are often described as ‘torch-like’)."
My bolding.
That description could explain the damage and the heat in the area of the Ethiopian 787 ELT.
Addition:
A photo of a laptop with a thermal runaway from
Lithium-ion Safety Concerns ? Battery University
