Is it dangerous to jump start a dead battery? (Especially the way most guys do it?)

September 30, 2005

Dear Cecil:

Recently I gave a jump to someone who'd left his car headlights on and drained his battery. Because I have a healthy respect for anything containing moving parts, flammable liquids, and battery acid, I followed the directions for giving a jump in my owner's manual to the letter. These instructions run to seven pages. To summarize, they say to turn on the heater blower in both vehicles to prevent damage from voltage surges, turn off all other switches and lights in both vehicles, connect and disconnect the jumper cables in the order specified (positive terminal of dead battery, positive of booster battery, negative of booster battery, body BUT NOT negative terminal of dead car), and let the booster car run for several minutes before trying to start the dead car. The guys from whom I had to borrow the jumper cables treated me like an idiot, insisting that they just slap the cables on in any order, doing nothing more than going from red to red and black to black without bothering with other precautions. My question is this: Is it really necessary to be anal when jump-starting a car? What could happen if I used the slapdash method? Are there any real-life instances of terrible consequences of haphazard jump-starting (but spare me the gory details if the answer is yes)?

Don't worry, ma'am. The scarred-eyeball photo I found online wouldn't reproduce very well on newsprint anyway. Let's just stick to the facts:

(1) Yes, there are real-life instances of terrible consequences of haphazard jump-starting. They mostly involve eye injuries due to car batteries exploding in the faces of mopes who just slapped the cables on. I haven't been able to firmly ascertain how often this happens, which has some bearing on how seriously you should take that stern advice in your owner's manual. But it's not like somebody just made the whole thing up.

(2) Car batteries can explode due to detonation of hydrogen liberated by electrolysis of the water found in lead-acid car batteries. Some circumstances, like extreme heat or cold, are especially conducive to electrolysis.

(3) In light of the above, the seven pages of instructions in your owner's manual consist of sensible things all car owners should do. Space doesn't permit reviewing every step, but the key is attaching the last clamp to the car body, strut, etc., not the battery terminal. The last connection, if you make good contact, inevitably sparks, and you want said sparks to occur far from the battery, lest they cause a gas buildup to explode.

(4) Except for the rare Girl Scout such as yourself, however, nobody actually does this.

Which brings us back to the question of how often car batteries blow up. Little Ed has been calling around the federal government and so far it appears nobody keeps track of such things. (Hey, in Washington they barely notice hurricanes.) Case reports in the medical journals suggest battery accidents are fairly common--in 1978 an MD reported that his Chicago eye clinic treated 62 cases over an eight-month period. But nobody hazards a guess about the scale of the problem nationwide. Browsing on the Internet I found a couple car safety sites claiming that exploding car batteries cause 6,000 injuries annually. However, they cited no source.

Finally, Little Ed called a fellow named Carl J. Abraham, an engineer who described himself as the leading authority on exploding car batteries. Abraham told me that in the 80s he commissioned the Greater Detroit Society for the Blind (now the Greater Detroit Agency for the Blind and Visually Impaired) to survey eye doctors and hospitals and such on how many injuries they saw resulting from exploding car batteries. Apparent answer: 6,000-10,000 annually. The survey wasn't published in a professional journal, though, and I haven't been able to obtain a copy. (Abraham said he included his findings in a petition to the National Highway Traffic Safety Administration requesting safety standards for car batteries. The NHTSA denied the request.) The number seems high--surely we'd hear more about exploding car batteries than we do. In any case, Abraham believes it has dropped in recent years.

But the exact figure needn't concern us. Some nontrivial number of people gets injured by exploding car batteries each year. Doesn't that mean you should follow the seven pages of instructions in the manual despite what the boys think? For insight I called up the service manager for a car dealership. Did he know the correct procedures? He sure did. Did he and his crew follow them? They sure didn't. His main beef was that if you attached the last clamp to some remote point on the body of the dead car, you didn't deliver enough juice to crank the engine. My excuse for ignoring the procedure is similar: You often don't get a good connection due to crud on the terminals, so you have to jiggle the clamps, most of which are unavoidably on battery terminals, till you see sparks. Is this a dangerous, stupid, typically guylike thing to do? Yeah. But nine times out of ten we'll be able to start your car.

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