LAPD blast containment truck fails, seventeen people injured 6

[jrs87]

https://www.dailymail.co.uk/news/ar...illegal-fireworks-LA-goes-terribly-wrong.html

Someone did not read the manual.

 

[dik]

Not knowing anything about it... that would be my kind of guess... I had no idea the 'projectile' could travel like that...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[RedSnake]

That could just be poor clean-up after the last use.

Well that is my point, why polish the whole truck and everything else up for this show off, but leave that if it was possible to clean it off.

I don't think the seal is particularly important in this design.

No as I sade it's only there to make it gas-tight when transporting things that can evaporate toxic gases.

I had no idea the 'projectile' could travel like that...

Frisbee you know. ;-)
Or maybe it's really a flying saucer.

/A


“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[RedSnake]

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[RedSnake]

It looks as if there could have been some change in the metal structure in this area from earlier blasts.

/A

 

[RedSnake]

I am not sure what kind of regulations applies for this blast containers.
At least here on the European side it's seems the normal procedure is to use them for transport and then take things out and blast them in another places.
And if there is a explosion during transportation, at is still safe.
There surely most be some limitations for how many blasts can be done inside this blast containers before they are deemed insecure for use.
At least there should be a X-ray or ultrasound examination after every inside blast or something.
I would like to say that a yearly inspection would not do it, in this case.

At least the SE Dynasafe is rated for "Number of Repeated Detonations" usually 10 there is some that can only take 1 but then we are talking 20kg TNT.
Abd the smaller one 5 and 8 kg (TNT) seems to be made only for transport.

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[RedSnake]

NABCO Model-64 GT-SCS:

• Rated for unlimited detonations of 6.8 kg/ 15 lbs. Military C-4
• Rated for one-time detonation of 11 kg /26 lbs. TNT

15lb= 6.803885kg, 26lb= 11.79340kg

https://store.mssdefence.com/home/1...f-closing-total-containment-vessels-home.html

Dynasafe

DYNASEALR X10
Explosive Rating (DDESB Approved) 5 kg / 11 lbs. TNT-eq
Number of Repeated Detonations 10
Maximum One-Time Detonation 15 kg / 33 lbs. TNT-eq

DYNASEALR X12
Explosive Rating (DDESB Approved) 8 kg/ 17.64 lbs. TNT-eq
Number of Repeated Detonations 10
Maximum One-Time Detonation 20 kg/ 44 lbs. TNT-eq

https://dynasafe.com/containment/eod-bomb-squads/dynasealr-x-series/

It is clear that there is a difference in security thinking here.
The NABCO there you can explode as many 6.8 kg Military C-4 as you like but it can only handle an explosion of 11 kg TNT.
While the SE Dynsafe may only be used 10 times with 5 kg TNT and is only allowed one blast with 15 kg TNT.
It's has 25% security margin on the 5 kg. (6,25 kg/18,75 kg)

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[LittleInch]

That clamp type design might look big and strong, but I think it is rather weedy and open to stress concentration, over tightening and you start at a high level of stress in the clamp to clamp it tight then go and add a load more.

We have no idea at the moment how many times that chamber was used?

But shock loading needs a FOS of at least 3 IMHO. There is no way that chamber closure is strong enough for that.

At the root cause, a clamp design is a poor choice of closure mechanism for such a shock loading condition.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[waross]

f you think about it, a 24 inch diameter lid with 4500 psi applied to it and travelling 0.010 inch gains some 240,000 ftlbs of energy so a tiny amount of movement can generate tremendous amounts of energy.

I thought about it and I came to the conclusion that one of us has a busted calculator.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[IRstuff]

Thanks, I'm glad I'm not the only one.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

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[IRstuff]

Nevertheless, if the LAPD had decided to transport it, and it did explode while on route, a lot more people might have been injured.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[jrs87]

The photos of the truck from the fair are 12 years old. We have no idea of actual vessel history, but at hundreds of thousands dollars each, they are not disposable. LAPD released statements that they did not overload vessel. But they quoted onetime rating, not accumulative... This vessel would require impeccable record keeping...

On the stained flange at 6 and 12 o'clock, you can observe two clean rings in the stain. This indicates perhaps the hatch is rotating against the flange during detonation. (Note I do not mean the hatch is spinning against flange, think Challenger solid rocket case rotation of joint.) Or perhaps the rings are from vibration when the whole thing rings like a bell? Note they occur where the clamp is discontinuous.

 

[jrs87]

The black material on the I.D. of the flange opening looks a little stained as well. Refer to high resolution flickr photo.

 

[TugboatEng]

Ignore my energy comment. I may have been drinking beer riding in the back of a ski boat when I did the "calculation". I used a product in place of a quotient.

 

[FacEngrPE]

I wounder what the remains of the clamp look like.
I agree the location where the clamp halfs join is a location where strain (and possibly bending) could be important.

The following is speculation.
Possible failure modes could include:
[ul][li]Explosive quantity was misjudged[/li]
[li]Service life limits were not observed[/li]
[li]Clamp was not tight.[/li]
[li]Door flexed enough that it's OD became smaller than the ID of the clamp.[/li]
[li]Clamp failed in bending[/li]
[li]Clamp failed by brittle fracture[/li]
[li]Probably a bunch more, as impulse shock on the inside face of the vessel can translate into a shockwave traveling radially through the steel shell, behavior is going to be dramatically different from steady state loading.[/li]
[/ul]

 

[TugboatEng]

Another problematic design feature I see is that the mechanism that supports and operates the clamps is not actually attached to the vessel but to the frame instead. Any movement of the vessel would add additional stress to the clamps.

 

[jrs87]

Video of LAPD using this truck from 2015

https://youtu.be/ynC_lbETep4

 

[jrs87]

Is seems

https://www.nabcosystems.com/

was first created in 2016 with no obvious signs of being updated since.

Patent (Mistral)

https://patents.google.com/patent/US7506568B2/en

NAMCO and Mistral relationship is unknown to me.

https://www.gao.gov/products/b-412261

 

[jrs87]

See Figure 4 in patent PDF above. Clear areas in stained flange are simply the result of O-Ring seal.

 

[waross]

I would be very interested to know the details of the last use of the containment vessel for s substantial blast.
There may have been previous damage to the clamp ring.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jrs87]

Gases got past O-rings, pressurized unvented yoke, detached it? Corner stresses in yoke caused cracks to develop? Yoke and/or cover did not fully seat? Could a nylon strap from inside the vessel been draping over the flange when the cover was closed? Does operator pressure test vessel to confirm seal before detonation and/or transport is authorized?