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Help with physics in fiction.

Discussion in 'Off-Topic' started by stillman, May 16, 2013. | Replies: 10 | Views: 1046

  1. stillman

    stillman IncGamers Member

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    Hi. I'm writing an action story, and I don't know if this situation is possible. Here it is:

    A guy shoots at a hose/pipe/whatever on the side of a diesel tanker. Fuel sprays out and ignites instantly. He then drives the tanker over many city blocks, showering the lane and all the cars on the left side with fire. The tanker bashes over many smaller cars that get in the way, and the man must lean out the window to shoot tires out of cars in front. He eventually bails, and the tanker becomes a pillar of fire and smoke. The gun must be a revolver, but the fuel type, tanker size, and other details can change to make this happen.

    1. Will diesel in a hose or pipe ignite if shot?
    2. How many city blocks can someone drive like this?
    3. How good is air conditioning to prevent the driver from being cooked in the cab?
    4. Basically, what will stop this from working?

    There is also a human stampede chasing the tanker, and they are crowded on the right side because of the fire trail. The idea is that many blocks go up in flames, and the fleeing lynch mob clog up the streets and hinder the evacuation.

    6. How many people, roughly, are needed to jam the streets and get in the way of firetrucks for one block?

    Thanks.
  2. krischan

    krischan Europe Trade Moderator

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    1. No. Diesel has a too boiling temperature. Even gasoline doesn't blow up that easily. If you throw a cigarette stub into a puddle of gasoline, it will probably go out, but a puddle on an asphalt road in the hot sun might start burning. It will not cause an explosion that way.
    2. You don't need a bit gasoline on the road, else it will just be a boring fire while you probably want an inferno on one side of the road. Let's say you need a bathtub full (200 litres) per second, with a 20000 litre tank, at a speed of 100km/h. That's about 30m per seccond, i.e. it can travel 3km before the tank is empty.
    3. I guess you are safe from the Mythbusters on this one :). Let it break down at an opportune moment.
    4. It needs more than a bullet hole to let 200 litres pour out per second. You could make it a bazooka hit which didn't explode.
    5. I think you need more than those few people who happen to be in the street or live there to cause a stampede or to overcrowd it. Throwing in traffic accidents or other obstacles can probably help at that.
    6. I guess it's 4 persons per square meter, so a 10m wide road (which is rather narrow) needs 4000 people to be filled with humans over a length of 100m, but it might be much less with the mentioned obstacles.
  3. jmervyn

    jmervyn IncGamers Member

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    No zombies? I'm disappointed.

    There's any number of other flammables you could posit; maybe one of those? Propane is a no-go, and probably alcohol as well; it wouldn't ignite from a bullet, and if sparked it would "whoosh" in a very nice flame jet - probably hurling the tanker sideways with a big hole in it, rather than a flamethrower-y spigot. You want something with high flammability, but not necessarily explosive quality -

    I remember a very good web site with a lot of this sort of information, but can't find it any longer. Here's one that has some good material.

    P.S. Does he have to shoot the pipe? Couldn't he give it a good whack with an axe or something? Far more potential for your spigot that way.
  4. Stevinator

    Stevinator IncGamers Member

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    Well it's not the liquid, but the vapor that burns so quickly. What if the gas sprays out all over the street, and then something sparks it, and it burns up the street and makes the tanker explode? (a la diehard 2)? That's more plausible (though still unlikely), because the tanker draining would reduce the pressure in the tank, and might be enough to let the gas evaporate/vaporize--also the trail of gas is more flammable after it sits there for a little bit, because there's vapor coming off it. You can fudge a little, as long as it's plausible.

    But yes, the hotter out the more plausible, gas tends to be pretty temperature sensitive. BTW, I have put out a cigarette in a cup of gas. What they said above is totally true.
  5. stillman

    stillman IncGamers Member

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    100km/hr is way too fast for city driving. He'll drive under 50, just struggling to keep ahead of the mob. Hitting cars out of the way will also slow him. There should be enough fuel gushing out per unit area to make a river of fire.

    The hose would burn and melt away fast, leaving a hole the diameter of the hose. The problem is, the same would happen to the tires...

    The masses tweeted and organized to swarm this guy. In real life, similar incidents have happened in the US where enough people arranged to loot stores through tweeting. A hoard of strangers flood in, grab things, and leave without paying. The stores don't have enough security or time to get the police.

    He only has the revolver, and I can't change that. The best I can do is have him run up (stupidly, very stupidly) close and fire again so the muzzle flare ignites the vapor. Safer would be for a second shot to make a spark.

    I guess my main problem is getting it lit plausibly. After looking up flamethrowers on Wikipedia (which use petrol), I'm convinced the tanker would become a flamethrower on wheels. Cars would get doused, and their tanks would eventually go up too.

  6. jmervyn

    jmervyn IncGamers Member

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    Firstly, the hose wouldn't burn away - they're fireproof for starters. Flame doesn't lick around the opening like you imagine. Second, causing sparks with a bullet is FAR more random than you imagine, and why the military uses tracers (which have a dollop of phosphor in the backside of the bullet) for incendiary purposes. The bullet itself is generally made of lead, particularly if you're talking about the sort of ammo used outside of the firing range.

    Well, you asked.
    It really won't. There's no propellant, and the fuel doesn't aerate correctly just spouting out of an un-pressurized tank.

    Your video shows a tanker having already exploded; the fuel would already be heated and spread, so it's more like watching a tire burn.

    In the same fashion, cars don't just explode with a "KA-WHUMP!" noise, despite what movies would imply. There's tons of Mythbuster coverage that can help you out there. You get a far more enjoyable explosion when some old woman has been keeping cans of gasoline in her garage in the summer - THAT's some fireworks!

    I remember <MY> first disenchantment. The local rifle range/gun store produced a video of the effects various calibres have on regular cars. Anything below 9mm often didn't even make it through the door panel.
  7. stillman

    stillman IncGamers Member

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    Well, I'll have to play my "It's the future" card then. The hose is cheap rubber from lowered safety standards, yeah that's it. Things might get a little wordy having to contrive this to happen. But it will happen! It was already a hot and sunny day before I made this thread, so that will help with volatility.

    I think there would be a flamethrower effect. Even though the tank is unpressurized, the extreme weight of the fuel on top would force the bottom liquid out. It's like when you put your thumb over a running faucet; the smaller opening gives the flow more velocity. Wind and an irregular opening might spray the fuel out enough for air to mix in.
  8. BobCox2

    BobCox2 IncGamers Member

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    His shot missed and hits a nearby fireworks stand Setting in motion the inferno needed.
  9. LozHinge the Unhinged

    LozHinge the Unhinged IncGamers Member

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    Ask Matt Groening.

    It happens all the time on The Simpsons :nod:
  10. stillman

    stillman IncGamers Member

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    But you can't drive a fireworks stand through the city!
  11. jmervyn

    jmervyn IncGamers Member

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    YOU DIDN'T SAY IT WAS THE FUTURE!!! Non-standard version of gasoline, for teh win. Call it JP-15

    That way, you don't need pressure; the stuff can be self-aerating.

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