
Under Pressure - FatalLogic
http://minusbat.livejournal.com/180556.html
======
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.

~~~
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!

~~~
ashark
Back when I did this a few times a year, 20oz soda bottles made the best boom.
2-liter bottles couldn't take as many PSI and water bottles... well, they're
not designed to contain pressure. They'd fail at the cap, usually.

That may no longer hold, since 20oz bottles feel flimsier these days and all
have low-profile caps. Haven't tried in a while.

Also, PVC pipe burried in ground, drop dry ice bomb in, drop another bottle
with some water in it on top = dry ice mortar. Those little plastic bubble
things that toys in vending machines come in? A little dry ice, a little
water, close it, place lid down. POP, the bubble part flies a meter or so in
the air.

I will note for anyone trying this that the parent's ratios are very different
from what I used. Crushed dry ice to 1/10-1/8 full, about twice that much
water. Unusually warm water (say, from near the surface of a pond or lake in
late August) will _greatly_ reduce time-to-boom, so beware. Too little water
and it'll freeze before boom, greatly delaying or even preventing it. Very
annoying. Attaching to something heavy (but NOT shrapnel-genrating) and
sinking in ~5-10 feet of water is fun. Huge bubble, explosion can be felt on
land nearby.

------
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".

~~~
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 :/

~~~
lvs
Why? Nothing bad happened, so what is the point of punishing him? He learned
something and went home. So did everyone else.

~~~
greggyb
Endangerment is legitimately considered a crime.[0]

Our go-to example in an Economics of Law course was firing a gun while in a
crowd. Similarly, attempted murder is a crime even in the case where no harm
befalls the victim.[1]

[0][http://en.wikipedia.org/wiki/Endangerment](http://en.wikipedia.org/wiki/Endangerment)

[1][http://en.wikipedia.org/wiki/Attempted_murder](http://en.wikipedia.org/wiki/Attempted_murder)

~~~
lvs
The value of endangerment laws to society, to the extent that there is any
value, is to deter the offender and deter others as well. In the story here, I
don't see how you can apply that ethic. I don't want to live in the society in
which every low-probability danger is made into an offense. Life has some
sharp edges.

~~~
greggyb
Luckily there's a common sense rule to apply that an economic analysis of law
makes clear.

Enforcement should occur up to the point where the marginal cost of extra
enforcement is equal to the marginal cost of the activity we are seeking to
deter.

I would agree with you that the particular circumstance described in the
article does not warrant legal action, but your original post made no
allowance for enforcement directed at anything other than purposeful and
effective crime.

------
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...](http://en.wikipedia.org/wiki/Carbon_dioxide_data#Vapor_pressure_of_solid_and_liquid)

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

[3]
[http://en.wikipedia.org/wiki/TNT_equivalent](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](https://news.ycombinator.com/item?id=9449086)

~~~
maho
You are absolutely right, I should have used the formula for adiabatic
expansion.

However, I maintain that the pressure inside the thermos should only be 60atm,
since this is the vapor pressure of CO2 at room temperature [1], where the
liquid and the gas phase are in equilibrium. This is like the butane in a
lighter: Butane evaporates at room temperature, but there is an equilibrium
between liquid phase and gaseous phase when the pressure is higher.

Using 60bar and the adiabatic formula, I get 12.5kJ of energy.

[1]:
[http://en.wikipedia.org/wiki/Carbon_dioxide#Physical_propert...](http://en.wikipedia.org/wiki/Carbon_dioxide#Physical_properties)

~~~
TheLoneWolfling
Ok, that works.

I was just going from the article's figure of 100atm. I probably should have
double-checked that figure.

------
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.

~~~
arcatek
Probably the same feeling that when you lie to someone, see your lies being
slowly exposed, and there's nothing you can do about it. Happens a lot when we
are teenagers :)

------
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.

------
etaty
In picture:
[https://www.youtube.com/watch?v=Ldgp3Ton7R4](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?

~~~
ColinWright
I expect that the floor of the bin is elastic in the technical sense - it
returns to its resting form when no force is applied. When the BANG goes off
the base of the bin is compressed into the floor, hard. This lowers its center
of gravity. Then it returns to its previous shape, the CoG rising as it does
so. Once it has returned to its original position it discovers, rather to its
surprise, that it's now travelling upwards, and so it continues to do so.

~~~
TheLoneWolfling
You also have less pressure inside the bin than outside.

------
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.

~~~
r00fus
The 22 KJ seems widely varying form other estimates on this discussion (6KJ,
15KJ).

For example, is it clear that the pressure of 100 atm would actually be
attained by a simple thermos and dry ice? What lead you to use that number?

Furthermore, the .50cal round is focused on a small area, the impulse and
destructive force are multiplied by the shape of the bullet. Just like how
shape-charges magnify the explosive force of munitions to bust armor.

~~~
TheLoneWolfling
The 6KJ number is flat-out wrong. You cannot multiply pressure * volume like
that. It's not an isobaric expansion. I mentioned this in a reply to his
comment.

As for the 15JK number, I cannot see any estimates in this thread saying 15JK.
Could you link the comment?

The 100atm figure is assuming that the linked article's calculation of final
pressure is correct, assuming the thermos doesn't burst beforehand. Although I
fully agree that a standard thermos is unlikely to achieve that number.

And as I said a lot of the energy won't be focused. This is just a first
approximation, to indicate that yes, potentially the energy is there.

~~~
TheLoneWolfling
Edit, because YC locks comments for some absurd reason:

Apparently the vapor pressure of CO2 is ~60atm, which bumps the number down to
~12.5KJ. Though I haven't checked that number yet.

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

~~~
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...](http://www.kirotv.com/news/news/dive-shop-explosion-sends-tank-
shooting-through-pa/nbPfF/)

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

[http://abcnews.go.com/US/scuba-tank-explosion-kills-iraq-
war...](http://abcnews.go.com/US/scuba-tank-explosion-kills-iraq-war-veteran-
russell-vanhorn/story?id=14502395)

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

~~~
smoyer
Actually the article says that people are also killed by exploding truck tires
which are around 100 psi and further states that SCUBA tanks are pressurized
at up to 3000 psi.

~~~
abakker
Isn't the pressure only part of the danger? In my non-scientific experience,
it seems that the speed of failure is the important part. i.e a truck tire
with a nail in it does no harm, but a 15-ply semi tire at 100psi having a
catastrophic failure is a much different animal. All about the speed of
release.

My own personal story: some friends and I filled a 5 gallon bottle with a bit
of isopropyl alcohol, shook it up, and lit the opening to make a "rocket
flame". We had seen this done in class, and it went fine. BUT...we wanted to
do it again. we had no more alcohol, so we used Acetone instead, but it
wouldn't light. There wasn't enough air in the bottle, since we had just
burned out the oxygen. Because we were 16, and lacking much foresight, we
decided "why just put air in the bottle, when we could use pure oxygen from a
welding tank?". We did that. The ensuing incandescent explosion lit up briefly
like a lightbulb and then ruptured the bottle into about 100 pieces. the major
one landed 2-3 seconds later, about 200 feet away.

Even though that was moronic, I pride myself for having worn welding gloves, a
face shield, ear plugs, and used a 12 foot handle with a match on the end. The
detonation left me feeling shaky and jittery for about 6 hours.

My point is, speed of failure is important.

~~~
smoyer
That story belongs over on the "Under Pressure" thread! -
[https://news.ycombinator.com/item?id=9444675](https://news.ycombinator.com/item?id=9444675)

~~~
abakker
I think it is?

------
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.

------
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.

~~~
drostie
If you're lucky then the top of the thermos is plastic.

Safe way to solve the situation with a metal thermos with a plastic cap: clamp
thermos to workbench, pre-drill hole in large sheet of plywood, drill through
pre-drilled hole into thermos. Depending on how complete the sublimation is,
there may be a boom and you, the plywood, and your drill may potentially get
kicked back a meter or two in the worst case, but your plywood shield would
likely spare you from any high-velocity plastic fragments that would cause you
injury. If you're lucky the pressure is still low enough that it just blows
plastic out of the spiral of the drill bit and there is little other than the
plastic shavings to work around.

You would definitely want to be wearing earmuffs though.

~~~
jamesdelaneyie
Funny. Being from a very rural area my solution would of been to walk outside
and hoof the bloody thing as far as I could into the surrounding fields and
have a cup of tae while waiting for the boom.

~~~
evan_
Being from a very rural area of the US my solution would've been to leave it
in a field and shoot it.

~~~
didsomeonesay
Reminds off the stories of unattended luggage getting shot by security
personnel at airports [1].

Aparrently, shooting is the preferred way to disarm potential explosives in
such scenarios.

[1] [http://lilyasussman.com/2009/11/30/im-sorry-but-we-blew-
up-y...](http://lilyasussman.com/2009/11/30/im-sorry-but-we-blew-up-your-
laptop-welcome-to-israel/)

------
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.

~~~
ohazi
Yeah, thinking about it some more, "wondering what I would have done" quickly
turned into "wondering whether I'd still have hands or a face right now."
Scary stuff.

~~~
abakker
Drilling a hole is not a good option. If there is significant pressure inside
then the hole will begin the explosion, not release the pressure. In an ideal
world, the best option is to puncture it from far away, which is difficult out
in a city. In the country, you might find someone to shoot the thermos with a
small rifle.

------
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.

~~~
anu_gupta
I've never seen anyone swimming in it - plenty of kayakers and narrow boats
though.

------
hmate9
Funniest story I've read in a while :)

------
arikrak
As long as he didn't put aluminum and Drano in the bottle..

------
curlyquote
The lesson of the story? Don't have kids.

------
emaniacs
wow, i listening Under Pressure by Queen while writing this comment. :)

~~~
teddyh
Ice ice baby!

(Sorry.)

[http://tailsteak.com/archive.php?num=25](http://tailsteak.com/archive.php?num=25)

------
JohnLen
This seems to be crazy. Invasion of privacy.

------
erikb
Please add a more descriptive title. Is that some kind of autobiographic short
story? Is it something that teaches how to be a better
entrepreneur/developer/designer? What kind of people would be interested in
reading that?

 _edit_ why is it so hard to say that there is a novel to read and not some
specific information? It's okay to be a novel, but some people don't want to
read novels.

~~~
FatalLogic
I submitted this. I would have preferred to use a more descriptive title, but
HN guidelines discourage changing titles.

"Otherwise please use the original title, unless it is misleading or
linkbait."

[https://news.ycombinator.com/newsguidelines.html](https://news.ycombinator.com/newsguidelines.html)

It's not misleading, I think, just uninformative.

~~~
erikb
That's good to know! I would interpret it differently, though.

The idea, as far as I see it, is that you don't use title changes to increase
the attention, e.g., avoiding to use upper case. But you should certainly use
the title to increase the information density, e.g. 'translate "10 Ways To Do
X" to "How To Do X,"'.

But I see your point.

