FAA rules do not cover lithium batteries, so the agency in 2007 set nine "special conditions" Boeing had to meet to ensure their safety. A year earlier, the FAA had set similar conditions for Airbus. Special conditions are commonly used to cover new technology for which rules have not yet been written.
In both cases, the Air Line Pilots Association International, the world's largest pilot union, said airplane fire is so dangerous that the FAA should require cabin crew to have fire extinguishers and training to put out a lithium-ion battery fire. "A fire from these devices, in any situation, is unacceptable," the union said, during the 787 approval process.
The FAA said it chose not to require special fire extinguishers and training because of the four redundant systems already in the Boeing system to prevent the battery from catching fire.
The ALPA said on Tuesday it is monitoring the investigation into the 787 battery incidents, but declined to comment while the probe is going on.
"It goes back to why this was approved in the first place," said Hidetake Sakuma, an aviation safety consultant and a former safety manager at Japan Airlines Co Ltd.
"Of course there were people asking whether this was really safe, but they (the FAA) approved it and the Japanese airlines never questioned it."
So in above article I see two important pieces of info:
The FAA said....prevent the battery from catching fire.
ALPA says: "A fire from these devices, in any situation, is unacceptable,"
Below is the link to the special conditions (again) and you can see that point one is the containment, which is currently under investigation with unknown outcome. Point two however is violated (twice now). I think the NTSB will come to a conclusion that there was a fire (contained or not) and it will be assessed if point 1 of the special condition was met - however point 2 was violated and led to the safety review followed by the grounding after the second violation. So IMHO I think they thought it could have been bad luck or a manufacturing fault. Now we reach the stage where the whole adaptation is being questioned. The containment might have just worked as designed - the problem is that point 2 of the special condition is violated.
(1) Safe cell temperatures and pressures must be maintained during any foreseeable charging or discharging condition and during any failure of the charging or battery monitoring system not shown to be extremely remote. The lithium ion battery installation must preclude explosion in the event of those failures.
(2) Design of the lithium ion batteries must preclude the occurrence of self-sustaining, uncontrolled increases in temperature or pressure.
Preclude synonyms: avert, cease, check, debar, deter, discontinue, exclude, forestall, forfend, hinder, impede, interrupt, make impracticable, obviate, prevent, prohibit, put a stop to, quit, restrain, rule out, stave off, stop, ward
There was a special condition which was violated and another is under investigation (containment). Both batteries have been ruled out as overcharged now. I said in an above post that regulations can change. Here is another quote doubting the decision to allow those batteries via a special condition - if the FAA takes back the special condition (which is not fulfilled anyways) the batteries have to be exchanged and replaced by another technology, which means drawing board, development, new software, testing, certification and many many month of grounding.
Problems with the 787's lithium-ion battery have sparked questions about why the FAA in 2007 granted Boeing a "special condition" to allow use of the batteries on the plane, despite the fact that they are highly flammable and hard to extinguish if they catch fire.
Boeing designed a special system that was supposed to contain any such fire and vent toxic gasses outside the plane, but the two recent incidents have raised questions about whether that was a good decision.