WASHINGTON, D.C. -- The National Transportation Safety Board provided its most detailed explanation to date from its investigation into the battery fire aboard a Japan Airlines 787. The fire on the plane was discovered after it landed in Boston on January 7th.

NTSB chairman Deborah Hersman pulled no punches about the incident and their findings.

The expectation in aviation is to never experience a fire aboard an aircraft. said Hersman, critical of the backup systems Boeing designed in the 787 to prevent and handle a large lithium ion battery fire.

The FAA conditionally approved these backup systems.

Boeing says it provided four redundant systems to prevent overcharging or undercharging, both of which could lead to battery failure and a fire. And in its worst case scenario, the plane was designed to vent smoke through an outlet on the plane to keep it out of the cockpit or the cabin until a fire burned itself out.

Those systems did not work as intended, said Hersman, then referring to a smoking battery aboard an All Nippon Airways 787 domestic flight that made an emergency landing last week. We have to understand why this battery resulted in a fire when there were so many protections designed into the system

Where does this investigation stand?

First, the NTSB still does not have a cause, but Hersman said, What we know so far, we know that the lithium ion battery experienced a thermal runaway, we know there were short circuits and we know there was a fire.

Thermal runaway is a condition where cells begin to overheat and can t be controlled. The individual battery cells swell and flammable electrolyte, the sticky goo inside the battery allowing it to work, is vented or pushed out of the battery.

The NTSB says thermal runaway can be the result of a short circuit inside a cell, but investigators do not yet know if the short circuits found were built into the battery as a manufacturing defect or a result of the thermal runaway.

Dr. Joseph Kolly, the NTSB s director of research and engineering, believes they can find out the answer to that question.

We re looking for contaminants or defects, Hersman said about the continuing investigation.

In a laboratory, the NTSB has already taken most of the battery apart from the Boston flight, disassembling seven of the eight cells inside the main battery case. The windings of lithium cobalt metal from inside the battery were laid out on a large table. Some cells look brand new, others resemble metal beer cans pulled from a bonfire.

Today in Seattle, the NTSB said investigators worked with Boeing to download the data from two memory chips on the plane, which may tell them how much the battery was charged. Battery experts say overcharging could lead to smoke and fire.

While the plane s Flight Data Recorder showed the battery only received 32 volts, as designed, the NTSBclarified that does not rule out an overcharged condition.

The NTSB isn't sure when the investigation will finish.

If we have a breakthrough and we find something. That immediately points to a cause. We'll get that out as soon as possible, Hersman said.

She added that two shifts of investigators and engineers are working to figure out the problem, as the world s fleet of 50 Dreamliners sits grounded around the world.

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