Under Pressure

[Carlee]

I do explosions with liquid nitrogen almost daily at my job as a science demonstrator. We've had one accident where a bottle exploded in the hands of a college of mine. He got a good scar up his arm, but nothing deadly. He had to get sewn, but that was about it.

Most often though, if you fill up the bottle with too much nitrogen, it won't explode. It'll just freeze up and slowly disperse through whatever cracks are present. If it didn't explode over night, it probably wouldn't have at all.

I suspect it might have started to fizzle due to air leaving the bag, or due to a small leak, which is pretty harmless. Nitrogen explosions of half-litre bottles are very large, and can shake the ground 20-30m away. I can test it later today if time permits and upload a video, but overall, it would've been much clearer if it went off.

Edit: to people saying the cap is the weak point: 9/10 times it's the bottom that gives in first.

[Carlee]

https://www.youtube.com/watch?v=yiMIQk29iWg&t=30s

There's the product

[mixmax]

I have some experience with dry ice in closed containers.

Every now and then some friends and I will get some dry ice, a bunch of plastic bottles and other containers with a screw-on lid and have a laugh making small explosions.

Basically you take a bottle, fill it 1/4 with water and 1/2 with dry ice and screw the cap on. You then have around a minute before it explodes.

A 1/2 liter coke bottle will make a nice whooompf and a 20 liter plastic gasoline can (the largest we have tried) will make a bang that can be heard maybe half a mile away. They very rarely sizzle out, and the ones that do probably have a defect, or we didn't get the cap screwed on properly. There's some time pressure, so you don't stand around checking before you throw the container. I would imagine that a metal container will make a pretty big bang (higher pressure before it ruptures) and may throw out some nasty debris.

It's good fun!

[leni536]

> to people saying the cap is the weak point: 9/10 times it's the bottom that gives in first.

It may be the case for a typical water bottle but thermoses have much larger caps. The maximal force that a cap can hold is proportional to its perimeter (~r), the force itself is proportional to the area of the cap (~r^2) and the pressure. So larger caps can blow off by lower pressure. I would bet that for a thermos the weak point is the cap.

[davidw]

> I can test it later today if time permits and upload a video

+1 - I'm always up for a good explosion video!

[octatoan]

Sown?

[flarets]

Paraphrasing from that article: "So, realising I had created a bomb, I surrounded the bomb in shrapnel and took it to a crowded part of the city".

[mangeletti]

As soon as I read the bit about putting it in a bag packed with tile I was like, "this doesn't end well".

That was a pretty cool read.

[toothbrush]

Yeah, that guy should be arrested or at least given a heavy fine :/

"I had to keep zig-zagging to avoid pointing the bit which was going to explode at people coming up the street towards me" and "the canal is a crowded place on a Sunday morning"

My god, man :/

[maho]

A few calculations about the possible explosion:

- Assuming the inside of the thermos is at room temperature (and that there was enough dry ice initially), the pressure should be around 60bar. This is the vapor pressure of carbon dioxide at room temperature [1].

- At 60 bar and with a volume of, say, 1 liter, the energy available for the explosion is roughly 60bar x 1liter = 6kJ [2]. This is a TNT-equivalent [3] of about 1.5g, or about 10-100 firecrackers. Enough to cause injuries, but not enough for structural damage to a balcony [citation needed].

In my personal opinion, the most dangerous thing was handling the thermos. I believe letting the thermos sit on the balcony for a few days and closing doors and curtains (to prevent glas shards flying in) would have been a much safer alternative.

[1] http://en.wikipedia.org/wiki/Carbon_dioxide_data#Vapor_press...

[2] https://www.google.com/search?q=60+bar+*+1+liter&ie=utf-8&oe...

[3] http://en.wikipedia.org/wiki/TNT_equivalent

[TheLoneWolfling]

Your energy estimation makes no sense whatsoever. The figure you gave is for isobaric expansion, which is an entirely different beastie.

Also, he mentions ~100bar, not ~60 bar.

When I did a first approximation assuming adiabatic expansion, I got ~22KJ.

See https://news.ycombinator.com/item?id=9449086

[secretdark]

Great read, but speaking as someone who lives on one of those houseboats (and passes through Islington occasionally), please don't consider a canal a safe place to 'ditch' potentially exploding things in future.

[Wingman4l7]

"I looked at the flask with that awful sinking feeling you get when you realise you have created something which is inevitably going to explode at some point in the future, and there's nothing you can do about it."

[de_Selby]

A feeling we have all experienced many times before, no doubt.

[dsfsdfd]

Why not just put it outside on the balcony and leave it the hell alone? Fussing about it any more is just risking getting your hands blown off. Idiot. And all this faffing around with a time bomb while you have a kid to look after, totally irresponsible. Put a duvet over it and leave it alone. It's nearly Darwin award stuff

[dntrkv]

Seriously, why not just wrap it in blankets, put it all into some open lid container (trash bin, hamper, etc), and leave it on your balcony. There are so many better ways to handle this situation.

[maccam94]

I agree that handling this was dangerous, but I wonder how much damage the explosion would have caused if he hadn't thrown it in the river...

[etaty]

In picture: https://www.youtube.com/watch?v=Ldgp3Ton7R4

experiment start at 3:00

[oxplot]

Can someone explain how the entire bin went up? Does it mean that the explosion poked a hole at the bottom of the bin?

[drc37]

A few years ago while on vacation with my extended family, all my brothers and I decided it would be fun to drop dime size chunks of dry ice into a water bottle with a few inches of water in them and then throw them into the pool. We did this and given a few minutes they would explode, harmlessly - not much more than a fire cracker.

Then we had the bright idea of tying a 5lb weight to the water bottle and let it sink. This was a bad idea on our part. When it exploded, it sent a shock wave through the ground. It was pretty intense make us brothers kinda freak out. People rushed from inside the house and asked what explosion was. We were afraid we had cracked the pool, the concussion wave was so strong. Luckily, we hadn't for my brother's sake. It just makes me think twice before containing dry ice.

[r00fus]

Can anyone explain why putting a plastic ziplock or other bag around the thermos and hiding inside a cooler (or close-able container box) wouldn't be an adequate solution?

I imagine this isn't some pipe-bomb - the energy density simply isn't there - but you want to ensure that the thermos lid doesn't happen to injure some passer-by.

[TheLoneWolfling]

The amount of energy in a thermos like that is high enough that I'm not sure that would be safe.

Quick approximation, assuming adiabatic expansion:

Gamma for CO2 is ~1.29.

    Pf*Vf^y = Pi*Vi^y
    Vf = (Pi / Pf) ^ (1/y) * Vi
    Vf = (100atm / 1atm) ^ (1/1.29) * 1L
    Vf = 35.51L
    
    W = (PfVf - PiVi) / (y - 1)
    W = (1atm*35.51L - 100atm*1L ) / (1.29 - 1)
    W = 22.31 KJ

For comparison, a .50 cal round has ~15kJ of muzzle energy. Now, a lot of that energy won't be focused (if nothing else, the final temperature with adiabatic expansion is such that a large chunk should sublimate again), but still.

[ablation]

Curious: how much damage could this have done if it actually exploded? What kind of forces are we talking about here?

[Athas]

Not much. At the student revue last year, we had filled a thermos with dry ice, closed it up, and forgot about it on stage overnight. At some point during the night, it blew off the plastic valve at the top, which was ruined, but the metal flask itself was fine. The people sleeping near the stage reported a loud bang, but nothing else.

Hypothesis: since the valve is only going to be propelled by the expanding gases for a relatively short time before it has cleared the flask opening, I don't even think it accelerates to that great a speed.

Clarification: a thermos is more or less a best-case scenario, since the valve at the top is going to be much weaker than the flask itself. A plastic bottle is worst-case, because it is going to shatter and eject plastic splinters.

[zoba]

Could have seriously damaged his hand if he was holding it. I have a permanent scar in my eyebrow from dry ice enclosed in a weak water bottle that exploded a few (4 or so?) feet from my face. There are YouTube videos of people ending up with severe hand damage from 2 liter bottles.

I was cringing reading this article. I would never ever have handled one of these things, based on my experience. I think I would've put it in the fridge, left the house for at least a day, and bought a new fridge based on the damage.

[x0x0]

an aluminum scuba tank is filled to around 3k psi; they're quite energetic if they explode

http://www.kirotv.com/news/news/dive-shop-explosion-sends-ta...

This guy died and damaged cars 100ft away from the center:

http://abcnews.go.com/US/scuba-tank-explosion-kills-iraq-war...

Now, the article says 100psi not 3k, but you'd still probably rather not be near it.

[leni536]

Well I personally know a physics teacher who does extreme physical experiments using dry ice and liquid nitrogen. One simple experiment is pouring really little amount of liquid nitrogen into a 0.5l coke bottle then wait. We stood away from the bottle (~10m) and let it explode. It is really loud when it bangs, otherwise it's a safe experiment (of course it's done outside and you really shouldn't hold it in your hand).

What's the weak point of a thermos? It's definitely the cap. I think leaving it alone would have just sent the cap flying, it could have been safely done in a park.

[angusb]

That there was a continuous stream of small bubbles (as opposed to one gigantic one) suggests that the failure mode was a leak, not an explosion. Still, I would have been scared.

[bengali3]

The odd part is that submerging in a depth of water actually lessens the pressure differential making it less likely to explode, not more. So failure is less likely to occur as it's submerged further.

[TisButMe]

I'm not sure. The stream of bubbles could have been the remaining dry ice sublimating, couldn't it ?

[dijit]

thrilling read; interesting that the device manufacturers explicitly warn you against putting dry-ice in a thermos. I had never heard that before.. I mean, thinking about it- it makes sense, but I would not have reached the conclusion without assistance.

[jsymolon]

When I bought dry ice (last year) for the science fair, they do give out a safety brochure on handling.

One of the top 5 points, no tightly closing containers. Styrofoam cooler is ok and dry ice will last 2-3 days like that.

[davidgerard]

Pete is the sort of guy who needs a Skippy's List. See his LJ icon? That's a burning NextCube case.

[_anshulk]

My instinct would have been to cool it in some liquid nitrogen at the university and just safely let the dry ice out... Glad they had a canal nearby...

[bandrami]

Why not just puncture the thermos?

[Peroni]

He was working on the assumption that there was significant pressure built up in the thermos. Puncturing it would release that pressure causing a potentially dangerous explosion. The same premise as puncturing a balloon except the balloon in this case is made of metal and glass and the amount of pressure is significantly higher.

[ohazi]

It's a good idea to own a few basic tools, including a handheld drill and maybe a hacksaw, even if you live in a small flat.

Although in this case, depending on how long the thermos had been shut, I'm not sure whether attempting to relieve the pressure would have been the smartest move.

Now I'm genuinely wondering what I would have done...

[icebraining]

Like dsfsdfd said, leaving it on the balcony under a heavy blanket seems like the best option, though my first thought was just throwing it down the street sewers.

[JackFr]

My college roommate had a volumetric flask with water and dry ice explode in his hand as he held his thumb tightly over the top. No injuries, and we laughed at him for being an idiot.

[sschueller]

So the solution was the place the "bomb" in the public canal where it could hurt some poor swimmer or small boat when it eventually ruptures.

Seems very irresponsible to me.

[eru]

I don't think anybody swims in the canal in Islington.

[kranner]

It was the best solution he could think of at the time. That's not irresponsible, just human.

[hmate9]

Funniest story I've read in a while :)