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Old 10-31-2015, 02:02 AM
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Die Hard C4 Elevator

Forgive me if this has been asked before, but the Search function doesn't seem to be working at the moment. I watched Die Hard today for about the 100th time and once again there was something about the scene where two of the terrorists are shooting at the LAPD armored personnel carrier with a rocket launcher and John, frustrated, pulls out a brick of C4, jams three detonators into it, sandwiches it between a chair and a monitor, and tosses it down the elevator shaft, that bothers me. Aside from the other goofs in this scene (the size of the explosion, the massive fireball), would the detonators even set off the explosive without being connected to some sort of charge initiator? Or are the detonators themselves impact-sensitive?
Old 10-31-2015, 02:20 AM
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As primary explosives, detonators are sensitive to mechanical shock, but the manner in which they are used in the film would not be very reliable.

But then, John McClane wouldn't have survived jumping off of a roof woth a firehose wrapped around his waist or grabbing a duct opening with his fingertips after falling several floors, either. Die Hard, while remarkably consistent in plotting, operates in the realm of movie physics not far separated from Warner Bros. cartoons.

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Old 10-31-2015, 07:08 AM
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Quote:
Originally Posted by RearEchelon View Post
Aside from the other goofs in this scene (the size of the explosion, the massive fireball), would the detonators even set off the explosive without being connected to some sort of charge initiator? Or are the detonators themselves impact-sensitive?
Don't the detonators he uses have chemical timers? I don't recall attachment points for wires.
Old 10-31-2015, 11:14 AM
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They ise nonel (non-electric) detonators for the charges. The coil you see Heinrich walking around with is some kind of det cord, and you can see this later when Hans goes up to the top floor to examine the explosives, finding the det cord unattached. This is standard use for building demolitions because it can't be inadvertantly set off by ESD or a high power radio or microwave signal; the only electrical impulse is at the main initiator, which is shorted or inerted by a SAFE/ARM device that only functions when receiving a specified signal.

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Old 10-31-2015, 05:51 PM
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But when John jams the three detonators into the brick, you can see yellow and black wires coming out of the tops of them. I knew the yellow cord you see them wiring the roof with is det cord, which raises another question - wouldn't det cord, being a high explosive itself (IIRC it has a detonation velocity of somewhere around 22,500 fps), set off C4 without the use of detonators? If that is indeed the case, why such a fuss made about them?
Old 10-31-2015, 06:40 PM
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Detonating cord has a core typically made with PETN or RDX and a polymer plasticizer. It is fairly insensitive to mechanical shock and will burn without detonating in normal conditions, but can be set off by a direct pyrotechnic shock or slapper shock. Detonaters, on the other hand, have primary explosives that are sensitive to high mechanical or eletrostatic shock, as well as a deflagration-to-detonation transition above thr autoignition temperature. The small quantity and low aspect ot det cord makes it essentially impossible to initate and maintain auto-detonation from normal conditions; a detonation wavefront has to be initated by something else in order to get a sustained detonation.

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Old 11-01-2015, 09:20 PM
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Quote:
Originally Posted by Stranger On A Train View Post
But then, John McClane wouldn't have survived jumping off of a roof woth a firehose wrapped around his waist or grabbing a duct opening with his fingertips after falling several floors, either. Die Hard, while remarkably consistent in plotting, operates in the realm of movie physics not far separated from Warner Bros. cartoons.

Stranger
Why would he not have survived the fire hose jump? I assumed that the hose's reel provided enough resistance that he fell fairly slowly and the jerk stop at the end wouldn't have been that hard.
Old 11-01-2015, 10:13 PM
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Falling more than six feet being restrained by nothing but a hose around your waist would pretty much guarantee spinal injury. Also, note that the hose reel came loose during the fall and jammed up against the half-wall on the roof, so McClane had at least that much drop. He also would have been seriously injured busting through the plate glass window, perforated by bullets or no.

Die Hard gets credit for making the hero seem more human than most 'Eighties action heroes but allowing to be injured and bleed, but realistically, McClane would have been down by the end of the second reel.

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Old 11-02-2015, 04:06 PM
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Worth mentioning that old CRT monitors had high-level capacitors in them that retained a lot of juice, even when not plugged in. Tinkering with one could give a potentially lethal shock. Is that enough of a jolt to trigger a detonator?
Old 11-02-2015, 05:54 PM
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Only if in direct contact across the terminals of an electric detonator. Otherwise, it is highly unlikely. Despite all of the safety training and cautionary stories, inadvertant initiation of a detonator not wired into a circuit or in an explosive train is vanishingly rare. I once worked with a powder monkey who kept detonators loose in a sawdust filled box in the bed of the same truck he would transport hundreds of pounds of dynamite, Seismopak, and reels of debt cord (totally against DOT regulations, but this was a decade before the Oklahoma City bombing when enforcement was infrequent and inconsequential) and never had any accidents except for nearly demolishing his truck with an errant tree stump.

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Old 11-02-2015, 07:57 PM
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Quote:
Originally Posted by Stranger On A Train View Post
Detonating cord has a core typically made with PETN or RDX and a polymer plasticizer. It is fairly insensitive to mechanical shock and will burn without detonating in normal conditions, but can be set off by a direct pyrotechnic shock or slapper shock. Detonators, on the other hand, have primary explosives that are sensitive to high mechanical or electrostatic shock, as well as a deflagration-to-detonation transition above the autoignition temperature. The small quantity and low aspect of det cord makes it essentially impossible to initiate and maintain auto-detonation from normal conditions;
Apologies for the unrequested copyediting; the board's spellchecker was (and still is) hemorrhaging prior to my corrections.

The real point is...

Quote:
Originally Posted by Stranger On A Train View Post
a detonation wavefront has to be initated by something else in order to get a sustained detonation.
--Stranger
Does that mean there really was something to the portrayal of wrapping the C4 brick up with the CRT? The electrical shock from the CRT exploding would have been enough of a "detonation wavefront?"

---G?
Old 11-02-2015, 09:22 PM
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I can forgive the C4 blowing up since it made for a nice explosion. What bugs me, and I've never figured it out from that scene is why wasn't Huey Lewis and Fu-Man-Chu both killed in the blast? Plus how the hell did they both get back up the stairs to be killed later on.

Out of the whole movie that's always bugged me, everything else I can over look.
Old 11-02-2015, 10:33 PM
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The chair-bomb exploded when it hit the elevator on the floor where the rocket launcher was, which appears to be two or three floors above the ground floor. Presumably Huey and Mr. Endo were sufficiently shieded from the blast and able to make their way back up. The freight/express elevator was still working even at the end of the film.

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Old 11-02-2015, 11:37 PM
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Originally Posted by Edward The Head View Post
I can forgive the C4 blowing up since it made for a nice explosion. What bugs me, and I've never figured it out from that scene is why wasn't Huey Lewis and Fu-Man-Chu both killed in the blast? Plus how the hell did they both get back up the stairs to be killed later on.

Out of the whole movie that's always bugged me, everything else I can over look.
Not Fu-Manchu...Genghis Kahn
Old 11-03-2015, 01:01 AM
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I'm still unclear how the thieves were going to escape. Eleven of them cram into an ambulance that (somehow) none of the cops will notice is coming from inside the building's parking garage?
Old 11-03-2015, 07:26 AM
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Originally Posted by Stranger On A Train View Post
The chair-bomb exploded when it hit the elevator on the floor where the rocket launcher was, which appears to be two or three floors above the ground floor. Presumably Huey and Mr. Endo were sufficiently shieded from the blast and able to make their way back up. The freight/express elevator was still working even at the end of the film.
That's a possibility. It's hard to see where the C4 hit exactly. One of the local theaters usually plays Die Hard on Christmas Eve, I might have to go see it, just to look for that scene of course.
Old 11-03-2015, 08:34 AM
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Originally Posted by Bryan Ekers View Post
I'm still unclear how the thieves were going to escape. Eleven of them cram into an ambulance that (somehow) none of the cops will notice is coming from inside the building's parking garage?
The elevator is just for transporting Hans and the bearer bonds. Everybody else dresses as a rescue worker and walks out in the ensuing chaos. Remember, this film came out in 1988 when security around major terrorist events was still relatively loose. The more damning question is why they needed the FBI to cut the vault's power supply. Even if the circuits could not be cut off by manual operation, they should be able to physically cut through the power lead. They also seemed unprepared for the case that a party guest or someone else in the building might escape and make a signal (e.g. no guard in the stairwell to block off that route, not disabling the fire alarm, et cetera). In retrospect, the 'terrorists' don't seem to have quite as slick of a plan as they think. But if they did, even John McClane wouldn't have had a chance and there would be no story. Within the plot of the film (accepting the premise of the "German bearer bonds" and the ridiculous physics, the plotting is clockwork, which can hardly be said of recent action films.

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Originally Posted by Edward The Head View Post
That's a possibility. It's hard to see where the C4 hit exactly. One of the local theaters usually plays Die Hard on Christmas Eve, I might have to go see it, just to look for that scene of course.
McClane watches the elevator go down and stop at that floor. He earlier got a glimpse of the rocket launcher (or at least the crates containing it and the munitions) earlier in the film while escaping upward (though why they had it on such a high floor initially defies explanation since they clearly intend to use it from a lower floor).

And I watch this film every Christmas Eve. This, Trading places, and Kiss Kiss Bang Bang. "This isn't 'Good Cop, Bad Cop', this is fag and new Yorker. You're in a lot of trouble."

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Old 11-03-2015, 09:10 AM
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Here's what always bugged me about that scene (and I'm sure I'll be educated if my consternation is unfounded):

Let's just take for granted that an impact will trip the detonators; now, John shoves in one then two then says, "fuck it," and shoves in another. My question is ... what difference would that make? Wouldn't one detonator be sufficient to cause detonstion? If John had stuck 27 detonators in the thing would he have blown up LA completely?
Old 11-03-2015, 09:22 AM
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It just gives more likelihood of complete detonation. In demolition work, where getting reliable and complete detonation is mandatory, redundant detonators (usually in opposite sides of the charge) are frequently used. The effective energetic output of the main charge will be essentially unchanged.

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Old 11-03-2015, 09:35 AM
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You know, this can all be resolved with a simple test. Where's the nearest high-rise bank building?
Old 11-03-2015, 09:44 AM
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Originally Posted by Stranger On A Train View Post
McClane watches the elevator go down and stop at that floor. He earlier got a glimpse of the rocket launcher (or at least the crates containing it and the munitions) earlier in the film while escaping upward (though why they had it on such a high floor initially defies explanation since they clearly intend to use it from a lower floor).
I will have to pay closer attention the next time I watch it. I don't remember him watching the elevator, and I don't remember the rocket launcher being so close to the ground. The first time I thought it was up on 31 or so. I always thought the explosion took out the ground floor and thought the cop said something about it too. I'll just have to rewatch it.

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Originally Posted by Jack Batty View Post
Here's what always bugged me about that scene (and I'm sure I'll be educated if my consternation is unfounded):

Let's just take for granted that an impact will trip the detonators; now, John shoves in one then two then says, "fuck it," and shoves in another. My question is ... what difference would that make? Wouldn't one detonator be sufficient to cause detonstion? If John had stuck 27 detonators in the thing would he have blown up LA completely?
What did he care if he used 1,2 or 27 detonators, he didn't need them any more. I was under the impression that he just stuck them all in there to get rid of them, which is exactly what I would do, he doesn't need detonators, the terrorists do.

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Originally Posted by TriPolar View Post
You know, this can all be resolved with a simple test. Where's the nearest high-rise bank building?
Mythbusters, final season, final myth.
Old 11-03-2015, 06:35 PM
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Originally Posted by Edward The Head View Post
I will have to pay closer attention the next time I watch it. I don't remember him watching the elevator, and I don't remember the rocket launcher being so close to the ground. The first time I thought it was up on 31 or so. I always thought the explosion took out the ground floor and thought the cop said something about it too. I'll just have to rewatch it.
While the plot may be clockwork, I've always been bothered by the building geography. The party is on a high floor, but not the highest, right? (Doesn't McClane travel down with Tony's body?) One would think that the floor with the waterfall and for the big execs would be the top floor.

So what floor is the conference room/demo floor where Takagi gets it? It's close enough to the party that everyone hears the gunshot but close enough to the ground that McClane can hit a patrol car with a body thrown out the window.

As noted, the anti-tank missile was fired from a low floor but McClane saw it on a high floor.

And where was the vault?
Old 11-03-2015, 10:16 PM
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Originally Posted by bbonden View Post
And where was the vault?
The thirtieth floor!


Link

Last edited by Bryan Ekers; 11-03-2015 at 10:17 PM.
Old 11-04-2015, 11:10 PM
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Originally Posted by TriPolar View Post
You know, this can all be resolved with a simple test. Where's the nearest high-rise bank building?
Oh, well, it used to be right over there...

But, ummm, well....

Remember the end of Fight Club?



---G!
Old 11-05-2015, 08:51 PM
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Originally Posted by Stranger On A Train View Post
As primary explosives, detonators are sensitive to mechanical shock, but the manner in which they are used in the film would not be very reliable.

But then, John McClane wouldn't have survived jumping off of a roof woth a firehose wrapped around his waist or grabbing a duct opening with his fingertips after falling several floors, either. Die Hard, while remarkably consistent in plotting, operates in the realm of movie physics not far separated from Warner Bros. cartoons.

Stranger
Thanks for that. That perfectly explains how I feel about that movie but I couldn't find the words to explain it. Remarkably consistent in plotting nails it. That's why that movie was so refreshing to me.
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