Breaking Bad scene leading to GQish question

I jsut started watching Breaking Bad. How excellent.
My question has to do with a scene in episode 4, the end of the episode. Our hero takes a gas station windshield cleaning thingie (can’t think of the term for the sponge/squeegee combo…is there one?), opens the hood of a fancy sports car belonging to a guy he finds irritating, slaps it down on the battery…I think he makes the metal part of it connect to the two posts. He closes the hood, walks away, and a few seconds later the guys car blows up into flame.

Why? It can’t be simply water on the battery, that’s too scary and volatile, you could never risk water getting under the hood. So I guess it was the metal bar being wet and touching both posts? What exactly happens that would cause a a flaming explosion?

Since this ain’t GQ, I’ll offer a guess…the metal touching both posts created a short, which melted the battery enough to expose sulfuric acid fumes to a spark, leading to BOOM! Or the director just took a bit of dramatic license.

Someone that actually knows what they’re talking about should be along shortly to explain why I’m wrong.

A metal connection across the terminals of a battery is definitely a short. I don’t know precisely what would happen in this particular case, but short circuits in general cause a lot of heat, and a fire or explosion is certainly not out of the question. Ordinarily a fuse or circuit breaker would protect against this, but a metal bar directly across the terminals would almost certainly bypass any such in the circuit. The fact that the metal bar was wet would be basically irrelevant, except for possibly providing a better contact connection.

If it was an old battery, sometimes they leak hydrogen (i don’t remember why). It’s why they tell you to jump a battery with the negative to ground instead of on the negative pole of the dead battery. I think that’s what i’ve heard, but i could be mistaken.

Laying a wrench across the battery terminals can cause the wrench to glow red hot or at least (depending on the material) get very very hot. Many shadetree mechanics have done this at one point since the battery is a nice convienient tray to rest tools on. You can also melt right through the hood if you install an overly-tall battery in a car and the positive terminal touches the bare metal hood.

It could be an ignition source, but I also don’t really see it resulting in instant Hollyood-style explosion. Maybe if he had doused the spongy part in gasoline (and was sure to lay it on positive-to-negative to avoid sparking).

How did he open the hood? Aren’t most cars designed deliberately so that you have to go inside the car to open a hood?

The vibe I get from the show is that Walter White has such mad chemistry skills that they are almost a superpower. It is almost plausible that to blowup a car with the windshield cleaner, but not absolutely – for you, me, Chronos: and GreasyJack: But it is possible for Walter White.

Batteries can explode but I’ve never seen one flame for more than a second, much less a Hollywood explosion. I believe Red Skeezix explanation of hydrogen gas is the culprit rather than sulfuric acid fumes. Flames aside, an exploding battery can inflict serious damage to anyone standing nearby, as it flings battery acid in a wide radius.

This is why few cars have the battery in the trunk, where gases could build up. They would corrode any wires in the vicinity and if there were an accident, a spark would set them off.

I assume that electric cars that have batteries placed throughout the car have vent hoses to atmosphere. Hopefully one won’t run through a mud puddle and permanently clog any of them. If the battery can’t vent, gases will build up and explosively pop the case. There are advantages to placing a heavy battery in the rear of the car and I’ve done it with many autos without dire consequences. My biggest problem has been the resistance in the long cable that goes to the starter on the engine.

It was a convertible.

Weird, I wonder why my mom’s 10 year old or so Buick has the battery under the rear passenger seat. Before I just thought it was a weird, mildly inconvenient oddity.

Here is the scene in question. As suspected Walt lays the squeegee across the battery terminals, causing a short. The sparks caused by the short are pretty unrealistic; in real life you’d just end up with a very, very hot squeegee and perhaps some burnt or melted engine components. A car battery doesn’t put out very much voltage, so you don’t tend to get large arcs.

Now, theoretically, if the shorted parts are placed in just the right fashion, maybe it could cause a hole to be burnt in a fuel line, causing just enough gasoline vapor to escape to be ignited by an arc from the battery. That seems pretty unlikely, though. A good topic for Mythbusters.

My thoughts too. If the show was set in the 1950s and Walter White was a marijuana horticulturalist, I think he’d still be able to do this sort of stuff because he’s got Incredible Scientist Skills and thus has the ability to do Science! stuff that “regular” people theoretically can’t.

Got a clip of the scene?

There’s one little strip of metal on the squeegee. For metal to metal contact, the rubber part would probably need to be removed or the handle of the squeegee would need to be metal. It’s very hard to get that metal squeegee strip to touch anything because otherwise it would scratch glass as it was used.

My guess would be he used it as a tool to pop off the protective plate used to cover the battery acid container, or he used it to pull the ground wire off the frame of the car and connect it to part of the engine that has a fuel line.

Here’s the scene:

Looks like he backs up the metal strip on the top to connect the two posts. It immediately sparks/shorts. He closes the hood, smoke starts pouring out, and gets darker. Then about 10 seconds later - boom.

An explosion? Possible, though not particularly likely.

The sparks? I agree with friedo, unrealistic.

The ball of fire during and after the explosion? Pure Holllywood.

The look on the owner’s face when he sees the smoldering remains: priceless.

That is too funny, I’m picturing Tommy Chong, selectively breeding California Sensimia, until it can grab the legs of interloping NARCs. Kinda like Day of the Triffids. Funny that, why didn’t anyone try to smoke the triffids? They’re already from outer space, they might have been awesome.

Well, batteries are usually heavy and weight distribution can be improved by moving them to someplace that needs it. That would improve handling and in some circumstances, improve traction.

In a larger vehicle like a Buick they probably aren’t concerned with optimal handling. Google tells me that she has a LeSabre or an even older Riviera. The engine compartments of modern cars are pretty cramped, and batteries are diminished by heat.

They may have moved it out of the engine compartment to extend battery life, and in a car with many power accessories that may be very noticeable. I’d put my money on just running out of room up front though.

What would worry me is that the metal in the seat would short the battery. GM cars usually have their terminals on the side of the battery, so this would be helpful. Also, modern seats are mostly foam with a steel plate rather than the horsehair and bedsprings assembly that they once were.

I’ve had MGs where the batteries were behind the seats and Miatas and BMWs where the battery is in the trunk. Although I’ve seen exploding batteries scar people, I’ve never worried about these. The factories make allowances for these placements. I’ve sometimes circumvented the factory’s protections and still don’t worry. I would be very surprised if your Mom’s Buick doesn’t have a vent hose that runs through the floorboard.

After watching it, I would agree with this. This looks like a job for mythbusters.

When using jumper cables, if you cross lines you get an arc and a fried cable. The batteries do not explode. To get an explosion like that, gasoline would have to be involved. There’s actually very little gasoline in the engine, most of it is in the back in the gas tank. A stream is shot into the carburetor to cause combustion. The majority of the gas in not under the hood. Even the other liquids under the hood aren’t that flammable.

Yeah, when I said that an explosion might be plausible, I didn’t mean one like the one in that clip. That’s pure Hollywood.