Sometimes, as I’m driving along the highway, the driver of the car in front of me will flick his cigarette out his window, and the glowing ashes blow towards and under my car. I’m wondering if they could possibly ignite any gas or oil residue down there and cause an explosion. I seriously worry about this. Does anyone else? Can anything really happen?
No. Gasoline will only ignite if the fumes are concentrated, and underneath your car at 60 mph is hardly concentrated. Even if you had a puncture in your gas tank, the fumes would be blown away at 60 mph. Oil isn’t that flammable anyway; it won’t ignite at all unless it’s heated first. A crust of oil stuck to your car’s chassis, traveling along at 60 mph, isn’t heated enough to ignite.
And anyway, the glowing ashes are extinguished almost immediately. They aren’t in contact with anything flammable enough for long enough to start a fire.
Find something else to worry about. 
Worry about the fact that the guy in front of you is (a) smoking, and (b) littering. 
Also, remember that to have an explosion, you need to ignite gas/oil in some sort of container with enough oxygen to keep the flame going long enough to build up a critical amount of pressure. Unless your gas tank has a huge gaping hole in it that causes the cigarette to bounce off the ground and land in your tank, you should be ok. Even if your gas tank leaks, travelling at highway speeds will likely prevent the gas from igniting and following back up into your car. Obviously, if your tank leaks enough, it could happen, but you’d likely not make it onto the highway in the first place if you were gushing out fuel at that rate.
All that said, if you ever get a speeding ticket because you found it important to pass a police car after the trooper threw a lit cigarette out of the window and thus made you nervous to be behind him, if you can then show that the very car you were driving at the time did in fact subsequently catch fire, the judge will show a lot of sympathy. Not only will you get off the speeding ticket, you just might get the assaulting a police officer charge dismissed, too.
Who said that?
Our office manager threw a lit cigar butt out the car window. It came back in through the back window, and set the entire car on fire and burned the guy to death!
I always told him the cigars would kill him, but he didn’t listen.
The car may have burned, but did it explode? I mean like the gas tank lighting up and making a big fireball like you see in movies. I have personally witnessed 4 or 5 vehicles on fire, and none of them blew up. (I didn’t do it, nobody saw me, you can’t prove anything.) Not to say that it’s impossible, just hard to do.
My aunt tells a story about her high school days, when she (in the great flodnak family tradition) was a bandfag:
They were riding a bus to a football game on a warm September afternoon. All the windows were open. On the rear bench of the bus one of the Sousaphone players had propped his horn; he’d stuffed his jacket in the bell so he wouldn’t lose it. (Kids! Do Not Try This At Home!) One of the kids in the middle of the bus was trying to sneak a cigarette. The chaperone looked around, the kid got nervous and flicked the lit ciggie out of an open window.
It was blown back into the bus and landed on the jacket stuffed in the Sousaphone bell.
Ever see smoke pouring out of a Sousaphone…?
(There is no point to this story, I was just seized with an irresistable urge to share it.:D)
Well, you’ve certainly brightened my day…
[adds “flicked cigarette starts fire in sousaphone and everybody on the bus dies” to list of Things To Worry About]
Back when I used to smoke I flicked a cig out the window and it went back in and landed inside, through warped gap, between the vinil moulding and the car frame. BEHIND the panel. I had no idea until when driving 70 down the highway my car filled with the most acrid smoke, blinding and choking me… I pulled over and and jumped in through the back hatch, where there was also stored 2 gallons of model engine fuel. I had just come back from flying my RC plane. In jumping through the back hatch I crushed half of the wing. I then had to tear off the moulded vinel where the insulation behind it was burning, well smoldering really. I had to yank out the burning insulation with my bare hands. The heat warped the vinal and it never would go back right.
though I didnt burn or 'splode.
Only when my section leader was doing a really bitchin’ solo to “Little Bitty Pretty One” at one of the basketball games…
Gasoline is pretty hard to ignite with a lit cigarette. My best illustration of this goes back to my early teen years BC (before car). I was in a buddy’s garage helping him with his motorcycle. He had a pan full of gasoline that he was using to clean parts (kids, don’t try this at home). He also had a lit cigarette dangling from his lips (REALLY don’t try this at home). I pointed out my discomfort at the juxtaposition (or, more realistically, said “Dude, WTF are you doing? You tryin’ to blow us up?”). His response was to let the cigarette drop from his lips into the pan of gas (once again, KIDS, DON’T DO THIS AT HOME!!!). The cigarette made a comforting “PSSSST” sound as it was extinguished by the gas.
ONE LAST DISCLAIMER: do not play with gasoline and open flames. Think about this: a gallon of gas has enough energy stored in it to move a 4,000 pound hunk of metal (your car) ten or 20 miles at a pretty high speed, utilizing only about 30% of its stored energy.
This person is dangerously irresponsible and lucky to be still alive. While extinguishing a cigarette in a container of petrol is a neat trick, the real danger is that the cigarette in his hand or mouth will ignite a cloud of invisible petrol vapour which has a habit of rolling around near ground level.
No joke. That was why I said over, and over, and over “Don’t try this at home.”
The real threat isn’t the lit cigarette. It is the open flame that you use to light the cigarette. That’s why it is a bad idea to smoke around flammible, volatile chemicals. In order to smoke, you have to use an open flame at some point. This is much hotter than the lit cigarette, and a much better ignition source for the conflagration you are imagining.
My story was to illustrate the point that your car is DEFINITELY not going to blow up by driving over a discarded cigarette. And IRL your car will not blow up when you are in a gunfight with the cops and take a bullet in the gas tank. That’s Hollywood, folks.
[hijack]
Oh, and this guy has a lot of other reasons he is lucky to be alive. I’m pretty sure he’s indestructable, like the Highlander, or something. One time, he laid down his street bike to avoid a collision, and ended up with a torn-up knee and a lot of road rash. Exactly one year later (to the day), he was in another motorcycle accident. This time, it was going around a curve on a two-lane country highway. A large truck was coming the other direction, and was cutting the corner on the curve. My friend ended up in a head-on collision (with a closing speed much over 100mph). The result was many broken bones, internal injuries, etc. He recovered pretty quick (about 8 months). He doesn’t get out of bed on that date anymore (twice was enough).
[/hijack]
I’m wondering if they could possibly ignite any gas or oil residue down there and cause an explosion. I seriously worry about this.
The smoker coming the other way should be the one to worry if he/she flicks out a glowing butt that sails IN my window and down my collar. I swear, if this ever happens again, someone is gonna die! Just hearing about “smoker’s rights” gets my blood boiling and I’m from tobacco land; North Carolina. You see a lot of bumper stickers here that say “tobacco money paid for this car”. Now THESE cars might catch on fire some dark cold night! 