News reports about fires involving Tesla Motors’ “Model S” electric vehicle have played a role in the company’s recent stock price decline.  However, these fires should be viewed in perspective because they share a common root cause.  Two of the three fires occurred right after the driver accidentally ran over a dangerous road hazard, and the third involved a high speed, front-end collision.

A recent report[1] published by the National Fire Protection Association (NFPA) asserted that of all automobile fires occurring after collisions, 69% originated in the engine or wheel area, whereas only 9 percent originated at the fuel tank or along the fuel lines.  This fact indicates that whatever substance happened to be the first one ignited after a collision (e.g., combustible fluids or plastics), the energy for ignition (e.g., electric arc or hot surface) was most often located in the engine area.

It is obvious that a large number of “fuels” and “ignition sources” co-exist in vehicles during normal use with very low likelihood they will come together in a way that causes a hostile fire.  But collisions and road hazards can puncture reservoirs and deform insulating materials in ways that expose these elements to each other and create conditions for fires to start.  The greater the vehicle’s speed at the time of collision, the more likely it will sustain damage that compromises the protective barriers keeping fuels away from ignition sources.

So the question regarding Tesla’s Model S seems to be whether its barriers are adequate to protect its battery cells. At present,Tesla seems to believe their “armor” is adequate.  Their website even states “…you are 5 times more likely to experience a fire in a conventional gasoline car than a Tesla!”[2]

Unfortunately, their comparison misses two important points:

(1) All three of the Tesla fires involved collisions, whereas the baseline rate they used to compare conventional car fires included many additional (unrelated) causation factors;

(2) By far, the largest percentage of all vehicle fires occurs in vehicles that are more than 5 years old.  Most of these fires have causes rooted in inadequate maintenance, flawed service, or operator carelessness.

Since all of the Tesla fires involved collision damage, fires involving improper maintenance or operation of gasoline-fueled cars should be excluded from any contrasting evaluation.  The more salient electric versus gasoline vehicle comparison would be “fires per collision exceeding a certain speed differential”.  Although we don’t have any actual data, we expect a comparison of collision-related fires would yield incident rates more similar for the two types of vehicles than the Tesla blog suggests.

However, it remains to be seen whether older all-electric cars are in fact safer overall than older gasoline cars.  Since reservoirs for gasoline, engine oil, and transmission fluid are simply not present in electric cars, it may still turn out that fleets of electric cars experience fewer total fires per mile driven than fleets of gasoline or diesel cars, over their respective lifetimes.

One additional noteworthy statistic in the NFPA report is that there was a steady decline in both annual automobile fires and fires per mile driven over the 20-year period from 1988 to 2007. Today, significantly less than 190,000 car fires occur annually (down by about half from 1988), and fewer than 75 fires per billion miles driven occur nationwide (down by about two-thirds).

These statistics are good news for both car drivers and car manufacturers.