A sobering reminder of the hazards in adding plug-in capabilities to hybrids comes from reports that a plug-in Prius conversion was destroyed in a fire. The news spread quickly through the online community of plug-in enthusiasts, bringing calls for all known information to be publicized as quickly as possible.

During a routine drive on Saturday, June 7, an upholstery fire destroyed a 2008 Toyota Prius converted to a 15-mile plug-in hybrid by Hybrids Plus of Boulder, Colorado. The car was owned by the Central Electric Power Cooperative in Columbia, South Carolina.

On Wednesday, June 18, Hybrids Plus issued a statement on the incident. The company noted that it immediately notified all owners of its conversions, and asked them to stop driving until more was known. Along with A123 Systems, which made the lithium-ion cells used in the Hybrids Plus pack, it conducted two forensic examinations of the damaged car.

While the company hasn’t reached a definitive conclusion on the initial fault point, it did identify several safety improvements that could be made to lessen the chance of an upholstery fire like the one that destroyed CEPC’s car. It is now inspecting and upgrading all its vehicles in the field, starting with 15-mile Priuses, followed by 30-mile Priuses, and then its Ford Escape conversions.

“The study did establish with a high degree of confidence that the cells were not the cause of the incident,” said Hybrids Plus, “and that the vast majority of the cells were unaffected by the high temperature to which they were exposed.” Further, “the Hybrids Plus PHEV system also was able to withstand the high temperatures in that incident, remaining largely intact.”

The company also felt compelled to clarify several inaccuracies in various media reports on the incident. Its charger was not involved, said Hybrids Plus, and there was no “explosion.”

The following day, plug-in advocate CalCars issued a statement summarizing the facts and offering its opinions on the entire incident. It suggested from second-hand reports that software, connectors, or wiring may have been at fault. Davide Andrea, chief technical officer at Hybrids Plus, said simply, “I have nothing to add.”

CalCars also expressed regret that Hybrids Plus hadn’t immediately addressed the issue publicly. This may be a particularly germane topic for Ron Gremban of CalCars, as he recently suffered an electrical fault in his own converted Prius.

It is just these kinds of issues that terrify major automakers as they prepare to roll out their first plug-in hybrids in roughly two years. General Motors, in particular, may be first to reach production with both the much-publicized Chevrolet Volt and a plug-in version of its Saturn View Two-Mode Hybrid. Stringent safety regulations, and corporate memories of the lawsuits engendered by the hazardous “side-saddle” gas tanks in more than 10 million 1973-87 trucks, are only part of the worry.

As CalCars put it, “opinion leaders from automakers, utilities and national labs have expressed their fears that ‘one bad accident’ could set back the progress of PHEVs.” As one industry insider said, “Barbecue one family in a minivan with a large battery pack, and it’s all over for plug-ins.”

Surprisingly, John Hanson, a Toyota spokesman, was quoted as saying the company has “nothing against” converters who modify the hybrid cars with additional batteries, though the company also doesn’t endorse such products.

For perspective, while there were 250,000 gasoline vehicle fires that caused 445 deaths in 2006, our society seems inured to them. Perhaps we assume they’re a necessary evil—the inevitable cost of using a fuel containing so much energy that 1 gallon can transport a 6,000-pound vehicle fully 20 miles.