This weekend the LAPD seized an astonishing cache of fireworks from one person. At one point they detonated some of them in a bomb truck which, I had thought, was built for the purpose of containing or redirecting such explosions. Things did not go as planned:
The resulting blast, which was expected to be “safe”, absolutely destroyed their bomb truck, damaged numerous surrounding structures, and injured 17 people.
What went wrong here? Why was the blast sooooooo much bigger than they apparently expected?
“Clearly protocols were followed and pursued, but something happened in that containment vehicle that should have not happened and we don’t know why,” the chief said. “We intend to find out why.”
This article says that the LAPD bomb squad put the “improvised devices” that they found (bootleg homemade fireworks?) in some sort of containment vessel and detonated them, thinking that the containment would actually contain them.
There have been explosions in fireworks factories in the past. It may be black powder, but it still packs a punch, as the neighbors found out. Evidently somebody got too ambitious and tried to detonate too much at one go. But I thought those people knew about such things, it’s their job. (Or was?)
Less than 10 pounds of material was placed in the chamber, far less than its safety rating, Moore said. He described the material as 40 homemade devices the size of Coca-Cola cans with simple fuses and 200 smaller but similar devices.
“This vessel should have been able to dispose of that material,” he said. But instead there was a “total, catastrophic failure of that containment vehicle.”
Can ten pounds of high explosive, properly deployed, plausibly result in the damage seen in the video? Even in the absence of any sort of blast containment vessel? Just wondering whether to believe “ten pounds.”
At the other end of the spectrum, 5000 pounds also seems implausible; it’s hard to imagine a bomb containment vessel voluminous enough to even hold 5000 pounds of explosive (plus the explosive packaging material), especially if it’s a bunch of separate devices in shapes that result in a low packing factor.
Same reason why the paper shredder, wood chipper, garbage disposal, toilet, etc. fail.
“Godammit Johnson! You can’t put that much shit in there at one time!”
While smokeless powders (not black powder or gunpowder, which is just saltpeter, sulphur, and carbon black) used as propellants in modern firearm rounds are intended to be used in a deflagration (rapid burning) mode, double base propellants, which contain both nitrocellulose (NC) and nitroglycerine (NG) (or more rarely polyvinyl nitrate (PVN)), can potentially detonate if confined and subjected to a high pressure impulse. This is a known issue among handloaders using double base propellants and why it is important to load cartridges within specification lest your shotgun suddenly blow apart next to your precious face.
My guess here is that the amateur pyrotechnics (‘fireworks’) were essentially pipe bombs made with a double base propellant in a confinement tube, and for some reason the EOD team dealing with disposal was either not aware or did not take this into consideration, resulting in unexpected energetic output and brisance that was beyond the capacity of the disposal chamber. Although the energetic mass of double base propellants is only a fraction nitroglycerine, pure NG can have an energetic output of up to 200% TNT equivalent, and under detonation conditions the normally stable NC will also contribute some yield, so even a few pounds of such a concoction could produce unexpected yield. Of course, it is also possible that the maker included some other high explosive mixtures such as PETN or TNT in the mix but that would require additional expertise to make without blowing ones hands off that is easily within the experience of a chemistry graduate student but not an amateur ‘fireworks’ maker.
Although that explosion looks very impressive, the fact that it was reported that no one was seriously injured and no structural damage was done to surrounding buildings or the street indicates that it probably wasn’t that large of a yield. People are surprised about how much damage detonating even a small amount of high explosive can do, but this seems to have mostly blown out windows and damaged car bodywork; the video reports “overturned cars” but I don’t see any indication of that, and what is shown in the aftermath is consistent with at most a couple of pounds of TNT-equivalent high explosive. What you see in the movies with big fireballs and people being thrown backward but then getting up and ‘shaking it off’ is pure Hollywoodism; high explosives do not generally produce fireballs or mushroom clouds unless they are large enough to superheat the air, and if you are close enough to be thrown off your feet, your insides are going to be jellyfied by the pressure wave passing through you.
10 pounds?? 40 things the size of coke cans worth? Yoiks!!
Plus, I hope they were not explosives, but instead home-made fireworks, I.e. designed to launch, burst and produce spectacular patterns. Otherwise, they are just IED’s. I assume the this guy was knowledgeable in making such things??
But if it’s fireworks, intended to airburst, would it necessarily be just powder or would more interesting substances be involved?
Also, inside a container, the shock wave from the disposal initial explosion would have immediately triggered all the contained items at once, instead of timed out like a fireworks show.
I sure hope the rest of the material was stored safely distant if it wasn’t all loaded at once.
I saw a demo once of a blasting cap - about the diameter of a pencil, maybe two inches long, and it totally shredded an aluminum can inside a heavy duty steel pipe.
One view of the explosion shows it turning the car across the street on its side.
Watch the video again. There is at least one car that was overturned, visible at 0:36 at bottom-center of the frame, just above the text (better view around 0:46). More noteworthy, the bomb truck is pretty much destroyed.
Tom Scott has a nice video illustrating the difference:
Yeah, I saw that in the Reuters aerial footage of the aftermath. It looks like a car that was to the side and forward of the truck got shoved up against the curb and turned on its side, not actually overturned. The LAPD truck is certainly a write-off but there isn’t actually that much structure in the trailer and cab; I would wager that the chassis and powertrain are probably still usable. A large high explosive load with hundreds of pounds TNT equivalent explosive would have left no visible evidence of a vehicle, with all of the superstructure flung outward and the chassis bottom of a shallow crater.
A lot of the ‘explosions’ you see on film aren’t even actually explosions. There is a scene in The Bourne Supremacy in which agents are rushing to enter a house in Berlin where the eponymous character was reported, and because of an improvised trap it blows out the glass front of the house, flinging the agents back toward the streets. In reality, the window was just pre-scored sugar glass, the ‘explosion’ was vaporized gas blown through a fan and ignited, and the actors were pulled up and back out of frame by cables attached to harness they were wearing. The cinematography and sound editing makes it appear dramatic but in reality it was just a big wooshing sound and stuntmen being yanked back onto an inflated cushion just out of frame. The best part of the sugar glass is that you don’t even need to clean it up; just wet it down and let it dissolve.
I’m assuming there weren’t actually 5000lbs of fireworks in there. It seems they’re conflating or confusing or not understanding (or I am) the difference between the amount of fireworks seized and the amount detonated. But OTOH, maybe they’re really jammed them in there.
Regardless, I’m really surprised they did that in such a densely populated area with so many spectators. ISTM, they should have taken it out to a field or empty lot and done it there. It could have even been used as a training exercise, like when the fire department burns down a house to practice.
