Burnt 2011 Chevy Volt

Chevy Volt fire: What did NHTSA know and when did they know it?

The NHTSA released a detailed report of the Chevy Volt crash test and forensic investigation last week prior to this weeks House Oversight committee hearing.

On Wednesday this week the House Oversight Committee will take up the question, "Volt Vehicle Fire: What did NHTSA Know and When Did They Know It?" Among the speakers will be NHTSA Administrator David Strickland and GM CEO Dan Akerson. Conveniently the NHTSA closed their investigation last week and released a document about the fire incident answering questions about the timing of the investigation into the Chevy Volt fire.

The crash testing of interest came as part of NHTSA's New Car Assessment Program (NCAP) under the agencies policy of testing vehicles with "new technology". For 2011 they were especially interested in electrified vehicles with lithium-ion batteries, like the Chevy Volt. The program consists of frontal, side, electrical isolation and rollover tests. The post-crash rollover test is intended to test for leakage of electrolyte from battery powered vehicles, or fuel spillage from gasoline or diesel vehicles.

Between April 20 and May 12, 2011, Chevy Volt crash testing occurred at the site of an NHTSA contractor, MGA Research. Based on its performance in that test the NHTSA awarded the five-star NCAP crashworthiness rating. After the crash test the Volt was moved to a storage lot. This much we knew already, it's starting from this point that the NHTSA report begins to fill in details in the timeline.

The NHTSA report lists four crash tests in the April 20-May 12 period. Three were side impact tests, two of which caused intrusion into the battery pack, and it was the test on May 12 which caused battery coolant leakage.

On June 6 MGA's personnel notified the NHTSA that a fire had occurred over the weekend in the storage yard. They initially investigated a possible arson and it was local fire officials who did an initial scene investigation. Hughes Associates were also called in for a forensic investigation, on June 13-14, which determined it was the Chevy Volt that was the source of the fire. The fire scene included four other vehicles, and all were cleared of being the cause of the fire. The Chevy Volt was found to have had a pressure event (a.k.a. explosion) that blew out the windshield, followed by a fire. The fire caused the air bags to explode, as well as the rear hatch pneumatic cylinders. The fire was intense enough to cause the neighboring vehicles to catch fire.

The in-depth forensic investigation found the battery pack had not only been punctured, but that the pack had bent at the point of impact, and that cells near the impact point had been damaged. The report says there is a "good possibility that this physical damage produced an internal short within the cells that resulted in the release of flammable gasses (electrolyte) that were eventually ignited". Once some of the electrolyte gas ignited, the other cells will have heated up, releasing their own electrolyte, feeding the fire. Occam's Razor is cited at this point in the report because physical damage causing an internal short was the simplest of the possible scenarios investigators came up with.

The damaged vehicle and its battery pack were shipped to an NHTSA test center in East Liberty, Ohio, where Hughes Associates, the NHTSA and GM engineers did a forensic inspection and battery teardown. It was here that they learned a "transverse stiffener" had penetrated the battery pack tunnel, damaged battery cells and ruptured coolant lines. Hughes concluded at this time that battery damage and electrical shorts in the pack led to the fire.

On Sept 21, 2011, another Chevy Volt crash test was performed, with additional instrumentation and cameras. The car was monitored for three weeks, and the cameras recorded no intrusion into the battery pack, no coolant leakage, and no fire.

Separately to these efforts the NHTSA, Dept of Energy, Dept of Defense, worked to devise test procedures that would replicate the damage they saw in the Volt which caught fire. They designed an impact test and constructed rollover equipment for the battery pack. This led to the battery pack crash tests performed in mid-November 2011.

In the battery tests, each battery was impacted and then rotated in a method similar to the full vehicle crash tests. The battery coolant system was intentionally ruptured so that coolant could drip around onto the circuit boards inside the battery pack. They found the coolant to be conductive at high voltages, and that it could cause short circuits in the right conditions. In the November tests, one of the battery packs caught fire one week after the crash test, and in another sparks and flames jetted out when the pack was in an upside-down position. These sparks lasted about 1 second, and were due to shorts in battery wiring and circuitry.

Another set of battery tests focused on cell damage, shorting of the high power inter-cell connections (bus bars), and battery coolant leakage. Those tests were conducted in December 2011. In the December tests, one battery pack showed discolored wires indicating heating, but with no fire, and another battery pack caught fire 6 days after the test.

In yet another line of research the NHTSA and GM began investigating all crashes involving Chevy Volts as well as the two garage fires in garages containing Chevy Volts. None of the crashes, including some severe accidents, resulted in a fire. In both garage fires the Chevy Volt's were cleared of having caused those fires.

Additionally GM had developed a fix to mitigate intrusion of the transverse stiffener. This fix was installed into a Chevy Volt which was shipped to MGA where another side impact test was performed on December 22. There was no intrusion into the battery pack, no coolant leakage, and after three weeks of observation, no fire.

It's clear from this record of events that the NHTSA was not sitting on their hands but were performing an intensive forensic analysis. By November engineers had replicated the conditions of the fire in June, but the final report was unable to come to a definitive conclusion.

Back in 2008 when LG Chem was chosen as the cell supplier for the Chevy Volt (beating out A123 Systems), LG Chem's press release claimed their battery chemistry was not flammable. Anyone researching the history of lithium batteries knows of the potential for catastrophic fire, and that battery chemistry designers focus on many factors including non-flammability. However the NHTSA has shown that the electrolyte used by LG Chem, in the conditions of this test, become a flammable vapor. Which presents an engineering challenge to vehicle designers of the sort they face in designing gasoline fuel tanks (gasoline being a flammable explosive liquid). Namely, constructing the vehicle so the vulnerable portions are unlikely to catch fire. Fortunately the conditions identified in this test take quite a while, weeks even, to develop into a fire giving crash survivors ample time to get to a safe distance.

Ever since the fire became public knowledge GM has consistently stated that there must be a "depowering" following electric vehicle crashes. If the NHTSA had depowered the battery pack, the internal short caused by the crash test would not have been conducting electricity, and if the NHTSA conclusion is correct, the flammable electrolyte would not have caught fire.

Comments

One inconsistency it that the Volt's post-crash protocol calls for the discharge of the batteries (through a load, I'm sure), but the *experts* at NHTSA, who should know how to deal with crashed vehicles, didn't bother. Why were they so remiss? And the article provokes some questions. If "the coolant to be conductive at high voltages", what are they using as coolant? And what exactly do they mean by "conductive"? I would suppose regular Ethylene Glycol - Water, which is conductive in the ionic sense, but more conductive at high voltages? What do they mean by that? And how conductive? `~- Nehmo
That post-crash-drain-the-batteries protocol was developed following the forensic study of the crashed Volt. "Conductive" means conducts electricity, and that phrase came from the NHTSA report from their forensic study.
Incorrect. The protocol of de-powering the batteries after battery damage or the possibility of it was there before the crash. search: chevy-volt-catches-fire-weeks-after-crash-feds-probe/1 'Volt, spokesman Greg Martin said. "Had those safety protocols been followed for this test, this incident would not have happened," he said, adding that this is the only crashed Volt ever to catch fire.' and search: chevy-volt-fire-post-crash-test-protocol-slip 'The protocol not followed by federal testers, according to GM's spokesman was not "de-energizing the battery after the crash test." ' Moreover, in a a crash in the real world, GM’s Onstar system would report the crash and provides enough data to indicate if the battery was damaged. GM would then have the opportunity to follow up to see if the protocols were implemented. And of course I know "conductive" means the ability to conduct. But conduction of a material is an intrinsic value that typically doesn't change with voltage. Please re-read my post. There's no point in repeating myself. However, since I wrote that, I discovered what they really meant was that the liquid *when crystallized* (not when higher voltages are applied) becomes significantly more conductive. This is understandable, and it answers the question I said the words of the article provoked. Finally, if you want to cite something, then link to it (you should be able to post links here) and quote exactly you are referring to. `~- Nehmo
Where did the spark come from anyway? My guess is that the NHTSA did depower the vehicle right after testing. This seems like normal protocol. Thus, a depowering event causing a spark a week, 2 wks, or 3wks later could not have caused the spark that ignited the gas. Well take a look at your gas grill, more specifically the igniter. Within the typical house hold gas grill igniter exist a very powerful and exotic material. Yes, most have a material called PZT (Lead Zirconate Titanate) which is a very well-known and well-used piezoelectric material. Point being, LG Chem LTD also has this material in its batteries (just review their patents)! If it is not a short circuit created by the vehicle depowering causing the spark then what could it have been. Well, GM is standing by their statement that there was an internal short caused by depowering event even if it does not make sense. They are basically saying that the NHTSA does not know how to conduct a test. The same safety feature/material (i.e. inorganic piezoelectric particles) that LG Chem LTD puts into their Chevy Volt batteries, that supposedly prevents fires, is now turning around and biting them, and putting A123 System’s in front of the pack at the same time. In fact, this is the same material which caused GM to switch to A123 Systems for its new GM Spark EV (yeah me too, the fire is from a Spark and that's what they name their next, and best, micro-HeV??). This is the same reason why LG Chem LTD, after going back to the drawing board, filed another patent, currently in EU application phase. This patent application is not of the innovative type, it is of the damage control type. LG had to find a way to implement this piezoelectric effect (i.e. their inorganic piezoelectric particles), maintaining the same performance gains, keep with their supposed safety feature and win the next major HeV battery supply contract. At current, there is a very large and far reaching difference between LG Chem LTD and A123 System’s Lithium batteries and older Lithium batteries of just 4 or so years ago. LG Chem was the first out of the gate, and A123 System’s learned from their mistakes. A much safer implementation of the piezoelectric effect is possible without giving up the performance and high-rate cyclic performance. It’s a learning process and we will see GM jump horses many times in the future. These Lithium battery manufacturers are at war, there will be many step type increases in performance over the next 5 or so years. The resultant batteries will be of a new age and they will meet all our needs. The NHTSA should take a closer look and conduct a material analysis of LG Chem’s batteries and if these piezoelectric particles exist, and they are not electrically isolated from the chemical reaction process within the cell, they should consider that this material may have been the ignition source. This type of material can and should be used to make our batteries perform better and last longer and they can be utilized in a completely safe manner. ‘Call me maybe’ 413-579-7108 Piezoelectricity means that if you deform this material it will generate a voltage, and if you apply a voltage to it it will deform. So, in LG Chem's battery they put this material in to prevent a short-circuit upon an impact. The idea is the piezoelectric material will create voltage at impact and essentailly opposes the short circuit potential