Thermal Runaway Like Porn, You Know It When You See It

In discussing the ongoing problems with two lithium ion batteries on Dreamliners, top engineers at Boeing are taking the Justice Potter Stewart approach. Deliberating on whether the American right to free speech also protected obscenity, Judge Stewart said, "hard core pornography is hard to define,"  then he added "but I know it when I see it." 

Investigators at the National Transportation Safety Board looking into the event on a Japan Airlines 787 in Boston on January 7 say they know what they saw when they looked at cells from the battery; thermal runaway. In an update to reporters on February 7, board chairman Deborah Hersman was clear. "I'm not offering any opinions, I am offering facts and observations of what our investigators have done," she said.

A perpetuating increase in temperature from battery cell to battery cell was specifically addressed in the special condition issued to Boeing when the Federal Aviation Administration granted the company permission to begin using this controversial energy source on airplanes. In cases of thermal runaway, the "metallic lithium can ignite resulting in a self-sustaining fire or explosion," the FAA wrote. 

But if last week's press conference in Japan is any indication, Boeing thinks the phenomenon is, like porn, difficult to define. Boeing says it isn't thermal runaway unless it causes a catastrophic event on the plane.

"In our certification work, in our design and development at an airplane level, the fundamental thing that we worry about is making sure that the battery can't harm the airplane," 787 vice president Mike Sinnett said at the briefing.

During certification, Sinnett said engineers were convinced that there was only one cause for thermal runaway, overcharging the battery. As part of the required test regime it had to overcharge a test battery and contain any resulting problems. If there was no catastrophic effect, Boeing salespeople could use this linguistic dodge to tell potential customers the lithium ion batteries were not subject to thermal runaway. That was better than telling them it could contain one.

"We've worked with our customers to make sure they understand what we mean when we say 'thermal runaway' and they understand that we've taken the appropriate steps to ensure that that never happens," Sinnett explained.  "You can imagine the concern then when someone else uses the term differently and says there was thermal runaway." 

A United 787 in New Orleans. Photo by Marc A Wessels

If the Dreamliner grounding weren't such a full-blown and wide-ranging fiasco with hundreds of millions of dollars of not just Boeing's money but the money of its customers on the line, Sinnett's  wordsmithing would be comical. He actually told the reporters assembled in Tokyo, "Thermal runaway is defined in many different ways and the definition depends on the perspective of the observer." 

Because Boeing has more eggheads than a chicken farm, I found it quizzical that it would encourage a lack of clarity, so I asked the opinion of others familiar with the details of the investigation.

I learned that during certification, the company modified the common definition of thermal runaway  (read the wikipedia entry here)  to limit it to a reaction that proceeds to cause damage to the airplane. This is the equivalent of a doctor limiting a diagnosis of high cholesterol only to those patients who have suffered a heart attack. 

At NTSB HQ, some staffers are pouring over the tests while others examine the documents that led to the certification of the Dreamliner with those batteries on board. Boeing may try to make thermal runaway hard to define, but the investigators know what they have seen.

Watch the Boeing briefing in Japan here.