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The tragic physics of the deadly explosion in Beirut

264 points by ChuckMcM 6y ago

hn_throwaway_99 6y ago
Thanks for posting this - I wasn't previously aware of the delineation between a shock wave and a pressure wave that the author explained clearly. I'm curious, is there something specific about "high explosives" vs "low explosives", beyond just the magnitude of energy released, that explains why some generate shock waves and others pressure waves?
- a2tech 6y ago
  I've been led to believe that 'high' explosives are explosives that explode/combust faster than the speed of sound. Others (like black powder) burn slower.
  - hn2fast 6y ago
    More than just burn, 'high' explosives detonate [0], where the pressure wave itself provides the activation energy required to sustain the reaction. [0] https://en.wikipedia.org/wiki/Detonation https://en.wikipedia.org/wiki/Detonation
- erdos4d 6y ago
  In a nutshell, high explosives detonate, low explosives combust. The two processes are distinctly different in how they operate at the molecular level. Basically, detonation is when a shock wave goes through the material, causing it to "blow up" on a molecular level as it passes (the molecules split as the shock passes through). Combustion happens much slower and is usually a chemical reaction involving some sort of fuel and oxidizer that is mixed and burned. I'm not an expert, but you can see the difference in a gasoline engine. As you crank up the compression ratio the air/fuel mix in the cylinder will eventually undergo a change from combusting to detonating, producing engine "knock" and rapidly destroying your engine if you let it continue. On a gas motor, around 13:1 is a good spot to see this happen. Someone will have more for you, but I think this is the basic concept seperating the two.
  - TheSpiceIsLife 6y ago
    Am I right in my understanding then that diesel engines work entirely on the principle of detonation, and that's why they're heavier as everything is designed to cope with what would make a petrol engine ping? Does that make any sense? Or is diesel injected in to the cylinder in a way that more or less produces a controlled combustion?
    - refurb 6y ago
      Detonation in an engine means something different. Detonation is when the fuel starts burning from a source other than the spark plug and the two flame fronts collide.
    - crubier 6y ago
      No, Diesel engines are not based on detonation but also on a controlled combustion. The combustion is triggered differently that is all.
    - erdos4d 6y ago
      Diesel engines have a very high compression ratio, like 20:1 or more, but diesel fuel has a very high octane rating in comparison with gasoline, so it still combusts, not detonates, at these high ratios. What makes a diesel different than a gas engine is that the heat generated from the compression of the air/fuel mix is what actually causes the mix to start burning in the cylinder. So, for this reason you don't see any ignition system on a diesel usually, it doesn't need it (though maybe glow plugs or a block heater in cold areas, but not an actual ignition system). But the mixture still combusts in a diesel. Detonation is incredibly destructive to any engine, even a big beefy diesel. It can destroy any engine very quickly.
      - TheSpiceIsLife 6y ago
        Thanks all for clearing that up.
      - esaym 6y ago
        >but diesel fuel has a very high octane rating in comparison with gasoline, "octane" is the ability of a fuel to "resist combustion" from compression. Diesel fuel is not rated in "octane" but the opposite: the ability for it to combust from compression. For some reason in the "old days", it was commonly thought by some that by adding some diesel to gasoline that it would help "lubricate" the motor (as diesel does have an oily feel). However mixing diesel with gasoline only lowers its octane rating.
- mirimir 6y ago
  And if you're "inside" an explosion that's too slow to generate a shock wave, you may not even be seriously injured.[0] At least, if the pressure spike is too low to rupture your body. And as long as objects don't get accelerated toward you. As a child, a friend and I were electrolyzing water, in an enclosed space. And so the hydrogen flashed. But the concentration was so low that the air just turned faint blue. There was no damage, to us or the building. 0) https://www.stuff.co.nz/national/114372936/how-did-anyone-survive-the-christchurch-gas-explosion https://www.stuff.co.nz/national/114372936/how-did-anyone-su...
- tacon 6y ago
  The technical term for a subsonic combustion wave is deflagration.[0] A normal internal combustion engine deflagrates. If it starts pinging, that is detonation, and damages the pistons, etc. [0] https://en.wikipedia.org/wiki/Deflagration https://en.wikipedia.org/wiki/Deflagration
ChuckMcM 6y ago
I found this to be a well researched and very relatable piece of journalism with respect to the explosion in Beirut.
mirimir 6y ago
> In an explosion, however, the devilish little instigator that is oxygen shoves the process into overdrive. It's a great article, and I know that I'm being pedantic, but chemical explosions need not involve oxygen. For example, consider acetylene and silver acetylide, with a carbon-carbon triple bond. Or lead azide, with a nitrogen-nitrogen triple bond.
- AmericanChopper 6y ago
  > chemical explosions need not involve oxygen They do need an oxidiser though. Which may or may not involve oxygen. You’re right of course, but redox itself has some poorly chosen jargon.
  - TheSpiceIsLife 6y ago
    In chemistry, an oxidising agent (oxidant, oxidizer) is a substance that has the ability to oxidize other substances — in other words to accept their electrons. Common oxidizing agents are oxygen, hydrogen peroxide and the halogens. The jargon being that an oxidiser is an substance that can accept electrons, and doesn't have to by oxygen. https://en.wikipedia.org/wiki/Oxidizing_agent https://en.wikipedia.org/wiki/Oxidizing_agent
    - qubex 6y ago
      Just take oxidizer to me an “something that accepts electrons, like oxygen would”. Of course, there’s some oxidizers that can accept electrons from things that oxygen can’t (think of fluorine, for example) but... it’s just a term. There’s also an enormous continuum of timescales, all the way from the detonation of high explosives, to deflagration of low explosives, combustion of fuels, to... sedate rusting, which is just oxidation of iron or steel. YMMV.
  - mirimir 6y ago
    > They do need an oxidiser though. When lead azide detonates, you get elemental lead and diatomic nitrogen. So yes, the Pb++ oxidizes the azide. When acetylene detonates, you get a mixture of organic compounds. But I don't believe that there's any redox involved. You just get various hydrocarbons with single and double carbon-carbon bonds. And just to be clear, this is when there's no oxidizing agent present.
est31 6y ago
> Within that radius, the injuries from such a massive blast in a downtown location can be as varied as the victims who experience them, but a number of them are likely from glass and other flying projectiles. Flat, delicate, frangible, and installed in large sheets, glass is the perfect target for a blast wave of even minuscule magnitude; it shatters and flies easier than any other substance. The glass damage must be horrible. Your entire home covered in tiny pieces of glass. I hate when glass breaks at home because no matter how much you clean, it gets everywhere and months later you discover small shards in some distant place. Once I tripped on my way home after grocery shopping, almost at the destination. It wasn't even a big fall, but some glass bottles broke. They were next to plastic bags filled with oats. In the "recovery operations" I conducted afterwards, I threw away the remainders of the bottles and cleaned the oats bags under flowing water, to get rid of the glass bottle's contains on the bags. As I did this, I noticed the oats themselves getting wet, below the transparent plastic. I wondered, how can this happen, it's supposed to be water-proof. Then I found a tiny, almost invisible cut where a glass shard has entered the plastic bag. It was a big shard and I don't know what had happened had someone not noticed it and ate it. Horrified, I threw away the entire bag of oats, the risk of more, possibly smaller shards remaining was too big. Other bags which passed the "water test" I kept and I ended up eating their contents. I hope the people of Beirut are doing similar checks for their stored food, for their own safety. I read that many folks already have glass shards in their bodies due to the explosion but that's past damage that can only be managed. The future damage is preventable.
- interestica 6y ago
  > The glass damage must be horrible. Your entire home covered in tiny pieces of glass. Watch this video at .25x to really see how glass reacts in the pressure wave. You can see the look on the bride's face as the initial vibrations/sound reaches her. Then, you can actually see the window pane bow like a wind sail. https://youtu.be/PUQ-QvCqDjA https://youtu.be/PUQ-QvCqDjA
  - odysseus 6y ago
    Oh no. I really hope the bride and groom are OK!
fraserphysics 6y ago
Contrary to the article, I think amonium nitrate is a _high_ explosive. That means it can explode via a supersonic shock or detonation wave. https://en.wikipedia.org/wiki/Table_of_explosive_detonation_velocities https://en.wikipedia.org/wiki/Table_of_explosive_detonation_... says it's detonation velocity is 2.7 km/sec.
- jaclaz 6y ago
  Actually it is often not even considered an explosive, it is an oxydizer, the type actually used in mining is called ANFO (Ammonium Nitrate and Fuel Oil) and the oil (mormal diesel fuel) is added on-site: https://en.wikipedia.org/wiki/ANFO https://en.wikipedia.org/wiki/ANFO and has a much faster speed, around 4,200 m/s and only used in mining because it is extremely cheap and relatively more secure when compared to other (more powerful) explosives.
cpr 6y ago
https://mobile.twitter.com/COsweda/status/1292957525512294400 https://mobile.twitter.com/COsweda/status/129295752551229440...
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kevin_thibedeau 6y ago
Isn't the white cloud a de-pressurization front? The actual pressure wave is ahead of it and his speed estimate is probably low.
- toss1 6y ago
  Yes,you can see it quite clearly in the frame-by-frame in this video at between 2:15 and 2:25. The cloud wave is clearly expanding but it is behind the pressure wave that blows out windows on both the front and back (relative to the wave) of the highrise buildings. Spectacular and horrifying physics. https://www.youtube.com/watch?v=0tQ80Sj3QUs https://www.youtube.com/watch?v=0tQ80Sj3QUs
- ummonk 6y ago
  Correct. Adiabatic cooling due to depressurization causes temporary condensation. Though arguably it's more of a "back" than a "front", since it's in the wake of the pressurization front.
  - adolph 6y ago
    Does that make it like the vapor cone that appear around aircraft and launch vehicles sometimes? https://en.wikipedia.org/wiki/Vapor_cone https://en.wikipedia.org/wiki/Vapor_cone
    - ummonk 6y ago
      Yup, same cause (substantial temperature drop due to adiabatic expansion).
  - refurb 6y ago
    Makes sense. And my understanding of the "condensation wave" is that it's formation and dissipation is highly dependent on local conditions like humidity, temperate, etc. She claims that measuring the speed of that "condensation" wave proves it's not a shockwave, the actual shockwave can move faster than the "condensation wave" (because it's formation and dissipation is highly variable).
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x87678r 6y ago
here is an amazing view of the explosion. https://youtu.be/hp-n-ghagok https://youtu.be/hp-n-ghagok
- TheSpiceIsLife 6y ago
  I'd imagine this is approximately what Hiroshima and Nagasaki would have looked like, but the direction of the pressure wave would be different as they were both air bursts.
  - TylerE 6y ago
    You wouldn't have seen them...if you were looking in the direction you'd be blinded instantly. But really this isn't especially similar. There are plenty of videos of actual nuclear explosions.. e.g. https://www.youtube.com/watch?v=mP3bcPvgIG8 https://www.youtube.com/watch?v=mP3bcPvgIG8
    - roelschroeven 6y ago
      > You wouldn't have seen them...if you were looking in the direction you'd be blinded instantly. Feynman disagrees: https://www.realclearscience.com/blog/2016/04/what_its_like_to_actually_see_an_atomic_explosion.html https://www.realclearscience.com/blog/2016/04/what_its_like_... I don't think his statement "bright light can never hurt your eyes" is correct, and I think "I got behind a truck windshield, because the ultraviolet can't go through glass, so that would be safe" is pretty questionable: glass filters ultraviolet, but I don't think it blocks it completely. But fact is: Feynman looked at an atomic explosion and he wasn't blinded.
  - IAmGraydon 6y ago
    This is absolutely nothing like a nuclear detonation. The energy released was less than 10% of Hiroshima, but besides that, the detonation velocity of ammonium nitrate can’t even hold a candle to the near instantaneous energy release of a nuclear weapon. It’s the difference between a pile of gunpowder and a block of TNT, and even that comparison doesn’t do it justice.
psadri 6y ago
Seconds before the final explosion, you can see some flashes in the base of the smoke, like firecrackers going off. Anyone knows what these are?
- crististm 6y ago
  I think it was reported of fireworks explosion in the vicinity that lead to this event.
  - gwd 6y ago
    The whole "let's store fireworks next to several tons of explosives -- oh wait there's a fire" thing would sound incredibly contrived if it was in a story. It's almost like something out of a Road Runner cartoon, not real life.
    - makomk 6y ago
      Supposedly someone may have been carrying out welding on the building too, which makes the whole thing even more unbelievable.
      - gwd 6y ago
        According to this story, the welding was specifically as a result of the ammonium nitrate: > In January 2020, a judge launched an official investigation after it was discovered that Hangar 12 was unguarded, had a hole in its southern wall and one of its doors dislodged, meaning the hazardous material was at risk of being stolen. > In his final report following the investigation, Prosecutor General Oweidat “gave orders immediately” to ensure hangar doors and holes were repaired and security provided, a second high-ranking security official who also requested anonymity said. > ...During the work, sparks from welding took hold and fire started to spread, the official said. It's really mind-boggling. https://uk.reuters.com/article/uk-lebanon-security-blast-documents-excl/exclusive-lebanons-leaders-warned-in-july-about-explosives-at-port-documents-idUKKCN2562L3 https://uk.reuters.com/article/uk-lebanon-security-blast-doc...
    - 6y ago
moneytide1 6y ago
Why was so much NH4 stored in one place? Did a shipment of that size just arrive or has it been building up a stockpile? It is end of summer here in America, not sure what season is approaching outdoor Lebanese fertilizer schedules. Abundance of summertime high energy (summer solstice increased photovoltaic potential) could be the reason so much was purchased cheaply (infinite shelf life?)
- baryphonic 6y ago
  From what I've read, the supply had been in this warehouse for quite a while, having been seized from a Russian freighter that owed port fees or something. Certain people kept prodding the powers that be to take care of the situation before something disastrous happened, and they were not heeded.
- brazzy 6y ago
  It had been sitting in that warehouse since 2014, seized from a cargo ship.
  - moneytide1 6y ago
    I wonder if "sitting" because infinite loop bureaucracy ("seize" means potentially murky waters of international maritime law). From an economics standpoint - inefficient to leave energy dense "fuel" idle without being put to use for such a long period.
- gwd 6y ago
  The road to last week’s tragedy began seven years ago, when the Rhosus, a Russian-chartered, Moldovan-flagged vessel carrying ammonium nitrate from Georgia to Mozambique, docked in Beirut to try to take on extra cargo to cover the fees for passage through the Suez Canal, according to the ship’s captain. Port authorities impounded the Rhosus in December 2013 by judicial order 2013/1031 due to outstanding debts owed to two companies that filed claims in Beirut courts, the state security report showed. In May 2014, the ship was deemed unseaworthy and its cargo was unloaded in October 2014 and warehoused in what was known as Hangar 12. In February 2015, Nadim Zwain, a judge from the Summary Affairs Court, which deals with urgent issues, appointed an expert to inspect the cargo, according to the security report. The report said the expert concluded that the material was hazardous and, through the port authorities, requested it be transferred to the army. Reuters could not independently confirm the expert’s account. Lebanese army command rejected the request and recommended the chemicals be transferred or sold to the privately owned Lebanese Explosives Company, the state security report said. The report did not say why the army had refused to accept the cargo. A security official told Reuters it was because they didn’t need it. The army declined to comment. The explosives company’s management told Reuters it had not been interested in purchasing confiscated material and the firm had its own suppliers and government import licences. From then on, customs and security officials wrote to judges roughly every six months asking for the removal of the material, according to the requests seen by Reuters. https://uk.reuters.com/article/uk-lebanon-security-blast-documents-excl/exclusive-lebanons-leaders-warned-in-july-about-explosives-at-port-documents-idUKKCN2562L3 https://uk.reuters.com/article/uk-lebanon-security-blast-doc... It's not clear to me why, if they knew it was dangerous and had been asking for it to be removed for years, they decided to store fireworks in the same building.
qubex 6y ago
For all the horror, at least this happened at the quayside and half the explosive force radiated away almost harmlessly over the sea. That basically halved the actual destruction at the outset. If it had been in the middle of the city, there would have been twice the damage. This much is fairly obvious. What isn’t quite so obvious is that roughly half the energy was also wasted upwards, and that a startlingly worse case would have been if the explosives had been slightly interred, coupling the blast more closely to the ground and enhancing amplitude of the p-waves and providing plenty of really substantial debris raining down after basically ‘earth-quaking’ the buildings. Roughly combining the two 50% ‘wastages’ leaves you with about only one quarter of the energy was actually really channeled into destruction, which I’m going to be charitable and call a third. In ‘ideal’ conditions you might’ve had three times as much devastation, and that’s a pretty shocking thing to consider, given the actual carnage. NOTE: I had appended these considerations in a more inchoate form to the tail-end of another comment, but I figured I’d make them an item of their own and tidy them up a bit. Apologies for the duplication.
- FartyMcFarter 6y ago
  The grain store probably shielded a lot of other infrastructure and people too. However it seems very irresponsible to keep 85% of the country's grain in a single spot. It's scary how so many single points of failure exist.
  - qubex 6y ago
    Yeah I’ve been thinking about that too... harsh as it may sound, big concrete cylinders fillded with loose grain is pretty much the best pillow to cushion the blow you could think of. EDIT: As for the grain silos being “single points of failure”, that depends on the scope of the system you’re considering. Nationally, yeah... but internationally, there’s plenty and it’s being shipped in. So there’s actually more redundancy than the narrow-scope analysis would suggest. The 85% figure is just a figment of where one draws the borders, and national borders probably don’t have much valence in the given context (fortunately). Now, if we were speaking about 85% of the world’s ability to ship grain... now that would be a catastrophe of unimaginable proportions.
jacquesm 6y ago
This blast was reminiscent of what happened in Halifax long ago: https://en.wikipedia.org/wiki/Halifax_Explosion https://en.wikipedia.org/wiki/Halifax_Explosion To this date Halifax has a medical specialty: eye damage. People were looking at the fire on board the boat and ended up with plate glass shards in their eyes.
throwaway_pdp09 6y ago
How hard is it to not put nearly 3,000 tons of explosives in a city?
- doukdouk 6y ago
  Well, not putting explosives in a city is not hard; not putting substances that have some industry uses and happen to be explosive (eg fertilizer) near industry is hard. After all, it needs to be shipped, stored and used. If there's shipping, there will be some port city not far. And if there is industrial use, there will be workers, and some city as well to house the workers. See: - Halifax explosion (how hard is it to not make explosive-carrying ships go to ports?) - AZF explosion (how hard is it to not locate factories far away from cities?) - Texas City Refinery explosion (how hard is it to not let refinery workers inside the refinery?) - Tianjin explosions (how hard is it to not locate a port city near its port?) And so forth
- steelframe 6y ago
  When the government doesn't function, such a thing can be extraordinarily difficult. https://www.npr.org/2020/08/07/899776352/beiruts-explosion-looks-like-an-accident-and-a-sign-of-the-country-s-collapse https://www.npr.org/2020/08/07/899776352/beiruts-explosion-l...
neilv 6y ago
Separate from contemplating the physics, and hopefully not macabre rubbernecking of heartbreaking images of human suffering... what is being done for humanitarian aid for Beirut, and how can HN help?
- tgv 6y ago
  Probably by supporting the Red Cross, Medicins sans Frontiers, etc. Where I live, you can donate to all collaborating charities with a simple bank transaction. They state that €25 provides clean water for 10 families, €50 gets mattresses and blankets for two families, etc.
- Cthulhu_ 6y ago
  Loads of countries have sent search & rescue teams (the Dutch one returned after two days already because there was plenty of help on-site), hundreds of millions in relief funds have been gathered by countries across the world (https://www.al-monitor.com/pulse/originals/2020/08/lebanon-aid-conference-donors-pledge-beirut-france-macron.html https://www.al-monitor.com/pulse/originals/2020/08/lebanon-a...), charities all over are collecting, celebrities, companies and nations are donating tons (https://www.popsugar.co.uk/celebrity/george-and-amal-clooney-donation-after-beirut-explosion-47674696 https://www.popsugar.co.uk/celebrity/george-and-amal-clooney...), and local charities and donation numbers are being set up worldwide. HN can help by getting their super wealthy excessively profitable FAANG & co employers to donate money. Apple alone has $193 billion in cash on hand, more than twice as much as Lebanon's total GDP (https://www.cnbc.com/2020/04/30/apple-q2-2020-cash-hoard-heres-how-much-apple-has-on-hand.html); https://www.cnbc.com/2020/04/30/apple-q2-2020-cash-hoard-her... they could rebuild Beirut three times over and still have money left. Amazon has in the range of $70 billion cash on hand. Don't feel like you have to donate when it's corporations that hold (and hoard) all the wealth. Call them out on it if they offer a pittance. Apple / Tim Cook has indicated they will be donating, but no mention of how much: https://twitter.com/tim_cook/status/1291746412779069440 https://twitter.com/tim_cook/status/1291746412779069440 Couldn't find anything from the other big companies.
  - avh02 6y ago
    from what i've heard (informally) google is matching donations. edit: dug up the fb post a friend had about it, it appears to be an internal programme
bjornsing 6y ago
I didn’t read all the way through but quickly got the impression that the author got the physics wrong. Combustion and detonation are very different processes. It’s actually not easy to make ammonium nitrate detonate on purpose, and just heating it is certainly not a reliable way of making it do so.
ignoramous 6y ago
> Just after 9 am on December 6, 1917, in Halifax, mustachioed 45-year-old train dispatcher Vincent Coleman knew the lazy plume of smoke coming from the explosive-laden vessel in Halifax harbor was a terrifying portent of worse to come. But as the other dispatchers ran for their lives, Coleman realized the number of train passengers set to arrive at Halifax any moment, and so he stayed long enough to send one final telegram: “Hold up the train. Munitions ship on fire and making for Pier 6 ... Goodbye boys.” Coleman died in the blast at 9:05, but his final message saved thousands, not just the passengers on the trains that were able to stop before entering the zone of destruction, but also the citizens already in Halifax: The telegram signal reached every operator in the surrounding region, and because of Coleman’s quick thinking, every doctor who felt the earth rumble, up to 160 km away, had almost immediate access to news about what had happened. They rushed in to help. This particular tit-bit at the end of the article is a gem. Times like these tend to also bring the best in some of us.
- silasdavis 6y ago
  Indeed, thanks, I had missed that after skimming through the filler in that piece. https://en.m.wikipedia.org/wiki/Vince_Coleman_(train_dispatcher) https://en.m.wikipedia.org/wiki/Vince_Coleman_(train_dispatc...
- anonu 6y ago
  I had trouble understanding exactly how this scenario played out. Interestingly, Wikipedia gave some more color on the timing and distance involved [1]: The death toll could have been worse had it not been for the self-sacrifice of an Intercolonial Railway dispatcher, Patrick Vincent (Vince) Coleman, operating at the railyard about 750 feet (230 m) from Pier 6, where the explosion occurred. He and his co-worker, William Lovett, learned of the dangerous cargo aboard the burning Mont-Blanc from a sailor and began to flee. Coleman remembered that an incoming passenger train from Saint John, New Brunswick, was due to arrive at the railyard within minutes. He returned to his post alone and continued to send out urgent telegraph messages to stop the train. Several variations of the message have been reported, among them this from the Maritime Museum of the Atlantic: "Hold up the train. Ammunition ship afire in harbor making for Pier 6 and will explode. Guess this will be my last message. Good-bye boys." Coleman's message was responsible for bringing all incoming trains around Halifax to a halt. It was heard by other stations all along the Intercolonial Railway, helping railway officials to respond immediately. Also the Wikipedia about Vince Coleman [2] is missing the details from [1]. I guess this is part of the Wikipedia Wormhole people go through... [1] https://en.wikipedia.org/wiki/Halifax_Explosion https://en.wikipedia.org/wiki/Halifax_Explosion [2] https://en.m.wikipedia.org/wiki/Vince_Coleman_(train_dispatcher) https://en.m.wikipedia.org/wiki/Vince_Coleman_(train_dispatc...
amai 6y ago
From a scientific point of view it was unfortunate that no Rapatronic camera was installed in Beirut: https://interestingengineering.com/filming-the-first-milliseconds-of-a-nuclear-explosion-with-the-rapatronic-a-1950-engineering-marvel https://interestingengineering.com/filming-the-first-millise... https://en.wikipedia.org/wiki/Rapatronic_camera https://en.wikipedia.org/wiki/Rapatronic_camera

264 points by ChuckMcM 6y ago

Thanks for posting this - I wasn't previously aware of the delineation between a shock wave and a pressure wave that the author explained clearly. I'm curious, is there something specific about "high explosives" vs "low explosives", beyond just the magnitude of energy released, that explains why some generate shock waves and others pressure waves?

a2tech 6y ago
I've been led to believe that 'high' explosives are explosives that explode/combust faster than the speed of sound. Others (like black powder) burn slower.
- hn2fast 6y ago
  More than just burn, 'high' explosives detonate [0], where the pressure wave itself provides the activation energy required to sustain the reaction. [0] https://en.wikipedia.org/wiki/Detonation https://en.wikipedia.org/wiki/Detonation
erdos4d 6y ago
In a nutshell, high explosives detonate, low explosives combust. The two processes are distinctly different in how they operate at the molecular level. Basically, detonation is when a shock wave goes through the material, causing it to "blow up" on a molecular level as it passes (the molecules split as the shock passes through). Combustion happens much slower and is usually a chemical reaction involving some sort of fuel and oxidizer that is mixed and burned. I'm not an expert, but you can see the difference in a gasoline engine. As you crank up the compression ratio the air/fuel mix in the cylinder will eventually undergo a change from combusting to detonating, producing engine "knock" and rapidly destroying your engine if you let it continue. On a gas motor, around 13:1 is a good spot to see this happen. Someone will have more for you, but I think this is the basic concept seperating the two.
- TheSpiceIsLife 6y ago
  Am I right in my understanding then that diesel engines work entirely on the principle of detonation, and that's why they're heavier as everything is designed to cope with what would make a petrol engine ping? Does that make any sense? Or is diesel injected in to the cylinder in a way that more or less produces a controlled combustion?
  - refurb 6y ago
    Detonation in an engine means something different. Detonation is when the fuel starts burning from a source other than the spark plug and the two flame fronts collide.
  - crubier 6y ago
    No, Diesel engines are not based on detonation but also on a controlled combustion. The combustion is triggered differently that is all.
  - erdos4d 6y ago
    Diesel engines have a very high compression ratio, like 20:1 or more, but diesel fuel has a very high octane rating in comparison with gasoline, so it still combusts, not detonates, at these high ratios. What makes a diesel different than a gas engine is that the heat generated from the compression of the air/fuel mix is what actually causes the mix to start burning in the cylinder. So, for this reason you don't see any ignition system on a diesel usually, it doesn't need it (though maybe glow plugs or a block heater in cold areas, but not an actual ignition system). But the mixture still combusts in a diesel. Detonation is incredibly destructive to any engine, even a big beefy diesel. It can destroy any engine very quickly.
    - TheSpiceIsLife 6y ago
      Thanks all for clearing that up.
    - esaym 6y ago
      >but diesel fuel has a very high octane rating in comparison with gasoline, "octane" is the ability of a fuel to "resist combustion" from compression. Diesel fuel is not rated in "octane" but the opposite: the ability for it to combust from compression. For some reason in the "old days", it was commonly thought by some that by adding some diesel to gasoline that it would help "lubricate" the motor (as diesel does have an oily feel). However mixing diesel with gasoline only lowers its octane rating.
mirimir 6y ago
And if you're "inside" an explosion that's too slow to generate a shock wave, you may not even be seriously injured.[0] At least, if the pressure spike is too low to rupture your body. And as long as objects don't get accelerated toward you. As a child, a friend and I were electrolyzing water, in an enclosed space. And so the hydrogen flashed. But the concentration was so low that the air just turned faint blue. There was no damage, to us or the building. 0) https://www.stuff.co.nz/national/114372936/how-did-anyone-survive-the-christchurch-gas-explosion https://www.stuff.co.nz/national/114372936/how-did-anyone-su...
tacon 6y ago
The technical term for a subsonic combustion wave is deflagration.[0] A normal internal combustion engine deflagrates. If it starts pinging, that is detonation, and damages the pistons, etc. [0] https://en.wikipedia.org/wiki/Deflagration https://en.wikipedia.org/wiki/Deflagration

ChuckMcM 6y ago

I found this to be a well researched and very relatable piece of journalism with respect to the explosion in Beirut.

mirimir 6y ago

> In an explosion, however, the devilish little instigator that is oxygen shoves the process into overdrive. It's a great article, and I know that I'm being pedantic, but chemical explosions need not involve oxygen. For example, consider acetylene and silver acetylide, with a carbon-carbon triple bond. Or lead azide, with a nitrogen-nitrogen triple bond.

AmericanChopper 6y ago
> chemical explosions need not involve oxygen They do need an oxidiser though. Which may or may not involve oxygen. You’re right of course, but redox itself has some poorly chosen jargon.
- TheSpiceIsLife 6y ago
  In chemistry, an oxidising agent (oxidant, oxidizer) is a substance that has the ability to oxidize other substances — in other words to accept their electrons. Common oxidizing agents are oxygen, hydrogen peroxide and the halogens. The jargon being that an oxidiser is an substance that can accept electrons, and doesn't have to by oxygen. https://en.wikipedia.org/wiki/Oxidizing_agent https://en.wikipedia.org/wiki/Oxidizing_agent
  - qubex 6y ago
    Just take oxidizer to me an “something that accepts electrons, like oxygen would”. Of course, there’s some oxidizers that can accept electrons from things that oxygen can’t (think of fluorine, for example) but... it’s just a term. There’s also an enormous continuum of timescales, all the way from the detonation of high explosives, to deflagration of low explosives, combustion of fuels, to... sedate rusting, which is just oxidation of iron or steel. YMMV.
- mirimir 6y ago
  > They do need an oxidiser though. When lead azide detonates, you get elemental lead and diatomic nitrogen. So yes, the Pb++ oxidizes the azide. When acetylene detonates, you get a mixture of organic compounds. But I don't believe that there's any redox involved. You just get various hydrocarbons with single and double carbon-carbon bonds. And just to be clear, this is when there's no oxidizing agent present.

est31 6y ago

> Within that radius, the injuries from such a massive blast in a downtown location can be as varied as the victims who experience them, but a number of them are likely from glass and other flying projectiles. Flat, delicate, frangible, and installed in large sheets, glass is the perfect target for a blast wave of even minuscule magnitude; it shatters and flies easier than any other substance. The glass damage must be horrible. Your entire home covered in tiny pieces of glass. I hate when glass breaks at home because no matter how much you clean, it gets everywhere and months later you discover small shards in some distant place. Once I tripped on my way home after grocery shopping, almost at the destination. It wasn't even a big fall, but some glass bottles broke. They were next to plastic bags filled with oats. In the "recovery operations" I conducted afterwards, I threw away the remainders of the bottles and cleaned the oats bags under flowing water, to get rid of the glass bottle's contains on the bags. As I did this, I noticed the oats themselves getting wet, below the transparent plastic. I wondered, how can this happen, it's supposed to be water-proof. Then I found a tiny, almost invisible cut where a glass shard has entered the plastic bag. It was a big shard and I don't know what had happened had someone not noticed it and ate it. Horrified, I threw away the entire bag of oats, the risk of more, possibly smaller shards remaining was too big. Other bags which passed the "water test" I kept and I ended up eating their contents. I hope the people of Beirut are doing similar checks for their stored food, for their own safety. I read that many folks already have glass shards in their bodies due to the explosion but that's past damage that can only be managed. The future damage is preventable.

interestica 6y ago
> The glass damage must be horrible. Your entire home covered in tiny pieces of glass. Watch this video at .25x to really see how glass reacts in the pressure wave. You can see the look on the bride's face as the initial vibrations/sound reaches her. Then, you can actually see the window pane bow like a wind sail. https://youtu.be/PUQ-QvCqDjA https://youtu.be/PUQ-QvCqDjA
- odysseus 6y ago
  Oh no. I really hope the bride and groom are OK!

fraserphysics 6y ago

Contrary to the article, I think amonium nitrate is a _high_ explosive. That means it can explode via a supersonic shock or detonation wave. https://en.wikipedia.org/wiki/Table_of_explosive_detonation_velocities https://en.wikipedia.org/wiki/Table_of_explosive_detonation_... says it's detonation velocity is 2.7 km/sec.

jaclaz 6y ago
Actually it is often not even considered an explosive, it is an oxydizer, the type actually used in mining is called ANFO (Ammonium Nitrate and Fuel Oil) and the oil (mormal diesel fuel) is added on-site: https://en.wikipedia.org/wiki/ANFO https://en.wikipedia.org/wiki/ANFO and has a much faster speed, around 4,200 m/s and only used in mining because it is extremely cheap and relatively more secure when compared to other (more powerful) explosives.

cpr 6y ago

https://mobile.twitter.com/COsweda/status/1292957525512294400 https://mobile.twitter.com/COsweda/status/129295752551229440...

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kevin_thibedeau 6y ago

Isn't the white cloud a de-pressurization front? The actual pressure wave is ahead of it and his speed estimate is probably low.

toss1 6y ago
Yes,you can see it quite clearly in the frame-by-frame in this video at between 2:15 and 2:25. The cloud wave is clearly expanding but it is behind the pressure wave that blows out windows on both the front and back (relative to the wave) of the highrise buildings. Spectacular and horrifying physics. https://www.youtube.com/watch?v=0tQ80Sj3QUs https://www.youtube.com/watch?v=0tQ80Sj3QUs
ummonk 6y ago
Correct. Adiabatic cooling due to depressurization causes temporary condensation. Though arguably it's more of a "back" than a "front", since it's in the wake of the pressurization front.
- adolph 6y ago
  Does that make it like the vapor cone that appear around aircraft and launch vehicles sometimes? https://en.wikipedia.org/wiki/Vapor_cone https://en.wikipedia.org/wiki/Vapor_cone
  - ummonk 6y ago
    Yup, same cause (substantial temperature drop due to adiabatic expansion).
- refurb 6y ago
  Makes sense. And my understanding of the "condensation wave" is that it's formation and dissipation is highly dependent on local conditions like humidity, temperate, etc. She claims that measuring the speed of that "condensation" wave proves it's not a shockwave, the actual shockwave can move faster than the "condensation wave" (because it's formation and dissipation is highly variable).

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x87678r 6y ago

here is an amazing view of the explosion. https://youtu.be/hp-n-ghagok https://youtu.be/hp-n-ghagok

TheSpiceIsLife 6y ago
I'd imagine this is approximately what Hiroshima and Nagasaki would have looked like, but the direction of the pressure wave would be different as they were both air bursts.
- TylerE 6y ago
  You wouldn't have seen them...if you were looking in the direction you'd be blinded instantly. But really this isn't especially similar. There are plenty of videos of actual nuclear explosions.. e.g. https://www.youtube.com/watch?v=mP3bcPvgIG8 https://www.youtube.com/watch?v=mP3bcPvgIG8
  - roelschroeven 6y ago
    > You wouldn't have seen them...if you were looking in the direction you'd be blinded instantly. Feynman disagrees: https://www.realclearscience.com/blog/2016/04/what_its_like_to_actually_see_an_atomic_explosion.html https://www.realclearscience.com/blog/2016/04/what_its_like_... I don't think his statement "bright light can never hurt your eyes" is correct, and I think "I got behind a truck windshield, because the ultraviolet can't go through glass, so that would be safe" is pretty questionable: glass filters ultraviolet, but I don't think it blocks it completely. But fact is: Feynman looked at an atomic explosion and he wasn't blinded.
- IAmGraydon 6y ago
  This is absolutely nothing like a nuclear detonation. The energy released was less than 10% of Hiroshima, but besides that, the detonation velocity of ammonium nitrate can’t even hold a candle to the near instantaneous energy release of a nuclear weapon. It’s the difference between a pile of gunpowder and a block of TNT, and even that comparison doesn’t do it justice.

psadri 6y ago

Seconds before the final explosion, you can see some flashes in the base of the smoke, like firecrackers going off. Anyone knows what these are?

crististm 6y ago
I think it was reported of fireworks explosion in the vicinity that lead to this event.
- gwd 6y ago
  The whole "let's store fireworks next to several tons of explosives -- oh wait there's a fire" thing would sound incredibly contrived if it was in a story. It's almost like something out of a Road Runner cartoon, not real life.
  - makomk 6y ago
    Supposedly someone may have been carrying out welding on the building too, which makes the whole thing even more unbelievable.
    - gwd 6y ago
      According to this story, the welding was specifically as a result of the ammonium nitrate: > In January 2020, a judge launched an official investigation after it was discovered that Hangar 12 was unguarded, had a hole in its southern wall and one of its doors dislodged, meaning the hazardous material was at risk of being stolen. > In his final report following the investigation, Prosecutor General Oweidat “gave orders immediately” to ensure hangar doors and holes were repaired and security provided, a second high-ranking security official who also requested anonymity said. > ...During the work, sparks from welding took hold and fire started to spread, the official said. It's really mind-boggling. https://uk.reuters.com/article/uk-lebanon-security-blast-documents-excl/exclusive-lebanons-leaders-warned-in-july-about-explosives-at-port-documents-idUKKCN2562L3 https://uk.reuters.com/article/uk-lebanon-security-blast-doc...
  - 6y ago

moneytide1 6y ago

Why was so much NH4 stored in one place? Did a shipment of that size just arrive or has it been building up a stockpile? It is end of summer here in America, not sure what season is approaching outdoor Lebanese fertilizer schedules. Abundance of summertime high energy (summer solstice increased photovoltaic potential) could be the reason so much was purchased cheaply (infinite shelf life?)

baryphonic 6y ago
From what I've read, the supply had been in this warehouse for quite a while, having been seized from a Russian freighter that owed port fees or something. Certain people kept prodding the powers that be to take care of the situation before something disastrous happened, and they were not heeded.
brazzy 6y ago
It had been sitting in that warehouse since 2014, seized from a cargo ship.
- moneytide1 6y ago
  I wonder if "sitting" because infinite loop bureaucracy ("seize" means potentially murky waters of international maritime law). From an economics standpoint - inefficient to leave energy dense "fuel" idle without being put to use for such a long period.
gwd 6y ago
The road to last week’s tragedy began seven years ago, when the Rhosus, a Russian-chartered, Moldovan-flagged vessel carrying ammonium nitrate from Georgia to Mozambique, docked in Beirut to try to take on extra cargo to cover the fees for passage through the Suez Canal, according to the ship’s captain. Port authorities impounded the Rhosus in December 2013 by judicial order 2013/1031 due to outstanding debts owed to two companies that filed claims in Beirut courts, the state security report showed. In May 2014, the ship was deemed unseaworthy and its cargo was unloaded in October 2014 and warehoused in what was known as Hangar 12. In February 2015, Nadim Zwain, a judge from the Summary Affairs Court, which deals with urgent issues, appointed an expert to inspect the cargo, according to the security report. The report said the expert concluded that the material was hazardous and, through the port authorities, requested it be transferred to the army. Reuters could not independently confirm the expert’s account. Lebanese army command rejected the request and recommended the chemicals be transferred or sold to the privately owned Lebanese Explosives Company, the state security report said. The report did not say why the army had refused to accept the cargo. A security official told Reuters it was because they didn’t need it. The army declined to comment. The explosives company’s management told Reuters it had not been interested in purchasing confiscated material and the firm had its own suppliers and government import licences. From then on, customs and security officials wrote to judges roughly every six months asking for the removal of the material, according to the requests seen by Reuters. https://uk.reuters.com/article/uk-lebanon-security-blast-documents-excl/exclusive-lebanons-leaders-warned-in-july-about-explosives-at-port-documents-idUKKCN2562L3 https://uk.reuters.com/article/uk-lebanon-security-blast-doc... It's not clear to me why, if they knew it was dangerous and had been asking for it to be removed for years, they decided to store fireworks in the same building.

qubex 6y ago

For all the horror, at least this happened at the quayside and half the explosive force radiated away almost harmlessly over the sea. That basically halved the actual destruction at the outset. If it had been in the middle of the city, there would have been twice the damage. This much is fairly obvious. What isn’t quite so obvious is that roughly half the energy was also wasted upwards, and that a startlingly worse case would have been if the explosives had been slightly interred, coupling the blast more closely to the ground and enhancing amplitude of the p-waves and providing plenty of really substantial debris raining down after basically ‘earth-quaking’ the buildings. Roughly combining the two 50% ‘wastages’ leaves you with about only one quarter of the energy was actually really channeled into destruction, which I’m going to be charitable and call a third. In ‘ideal’ conditions you might’ve had three times as much devastation, and that’s a pretty shocking thing to consider, given the actual carnage. NOTE: I had appended these considerations in a more inchoate form to the tail-end of another comment, but I figured I’d make them an item of their own and tidy them up a bit. Apologies for the duplication.

FartyMcFarter 6y ago
The grain store probably shielded a lot of other infrastructure and people too. However it seems very irresponsible to keep 85% of the country's grain in a single spot. It's scary how so many single points of failure exist.
- qubex 6y ago
  Yeah I’ve been thinking about that too... harsh as it may sound, big concrete cylinders fillded with loose grain is pretty much the best pillow to cushion the blow you could think of. EDIT: As for the grain silos being “single points of failure”, that depends on the scope of the system you’re considering. Nationally, yeah... but internationally, there’s plenty and it’s being shipped in. So there’s actually more redundancy than the narrow-scope analysis would suggest. The 85% figure is just a figment of where one draws the borders, and national borders probably don’t have much valence in the given context (fortunately). Now, if we were speaking about 85% of the world’s ability to ship grain... now that would be a catastrophe of unimaginable proportions.

jacquesm 6y ago

This blast was reminiscent of what happened in Halifax long ago: https://en.wikipedia.org/wiki/Halifax_Explosion https://en.wikipedia.org/wiki/Halifax_Explosion To this date Halifax has a medical specialty: eye damage. People were looking at the fire on board the boat and ended up with plate glass shards in their eyes.

throwaway_pdp09 6y ago

How hard is it to not put nearly 3,000 tons of explosives in a city?

doukdouk 6y ago
Well, not putting explosives in a city is not hard; not putting substances that have some industry uses and happen to be explosive (eg fertilizer) near industry is hard. After all, it needs to be shipped, stored and used. If there's shipping, there will be some port city not far. And if there is industrial use, there will be workers, and some city as well to house the workers. See: - Halifax explosion (how hard is it to not make explosive-carrying ships go to ports?) - AZF explosion (how hard is it to not locate factories far away from cities?) - Texas City Refinery explosion (how hard is it to not let refinery workers inside the refinery?) - Tianjin explosions (how hard is it to not locate a port city near its port?) And so forth
steelframe 6y ago
When the government doesn't function, such a thing can be extraordinarily difficult. https://www.npr.org/2020/08/07/899776352/beiruts-explosion-looks-like-an-accident-and-a-sign-of-the-country-s-collapse https://www.npr.org/2020/08/07/899776352/beiruts-explosion-l...

neilv 6y ago

Separate from contemplating the physics, and hopefully not macabre rubbernecking of heartbreaking images of human suffering... what is being done for humanitarian aid for Beirut, and how can HN help?

tgv 6y ago
Probably by supporting the Red Cross, Medicins sans Frontiers, etc. Where I live, you can donate to all collaborating charities with a simple bank transaction. They state that €25 provides clean water for 10 families, €50 gets mattresses and blankets for two families, etc.
Cthulhu_ 6y ago
Loads of countries have sent search & rescue teams (the Dutch one returned after two days already because there was plenty of help on-site), hundreds of millions in relief funds have been gathered by countries across the world (https://www.al-monitor.com/pulse/originals/2020/08/lebanon-aid-conference-donors-pledge-beirut-france-macron.html https://www.al-monitor.com/pulse/originals/2020/08/lebanon-a...), charities all over are collecting, celebrities, companies and nations are donating tons (https://www.popsugar.co.uk/celebrity/george-and-amal-clooney-donation-after-beirut-explosion-47674696 https://www.popsugar.co.uk/celebrity/george-and-amal-clooney...), and local charities and donation numbers are being set up worldwide. HN can help by getting their super wealthy excessively profitable FAANG & co employers to donate money. Apple alone has $193 billion in cash on hand, more than twice as much as Lebanon's total GDP (https://www.cnbc.com/2020/04/30/apple-q2-2020-cash-hoard-heres-how-much-apple-has-on-hand.html); https://www.cnbc.com/2020/04/30/apple-q2-2020-cash-hoard-her... they could rebuild Beirut three times over and still have money left. Amazon has in the range of $70 billion cash on hand. Don't feel like you have to donate when it's corporations that hold (and hoard) all the wealth. Call them out on it if they offer a pittance. Apple / Tim Cook has indicated they will be donating, but no mention of how much: https://twitter.com/tim_cook/status/1291746412779069440 https://twitter.com/tim_cook/status/1291746412779069440 Couldn't find anything from the other big companies.
- avh02 6y ago
  from what i've heard (informally) google is matching donations. edit: dug up the fb post a friend had about it, it appears to be an internal programme

bjornsing 6y ago

I didn’t read all the way through but quickly got the impression that the author got the physics wrong. Combustion and detonation are very different processes. It’s actually not easy to make ammonium nitrate detonate on purpose, and just heating it is certainly not a reliable way of making it do so.

ignoramous 6y ago

> Just after 9 am on December 6, 1917, in Halifax, mustachioed 45-year-old train dispatcher Vincent Coleman knew the lazy plume of smoke coming from the explosive-laden vessel in Halifax harbor was a terrifying portent of worse to come. But as the other dispatchers ran for their lives, Coleman realized the number of train passengers set to arrive at Halifax any moment, and so he stayed long enough to send one final telegram: “Hold up the train. Munitions ship on fire and making for Pier 6 ... Goodbye boys.” Coleman died in the blast at 9:05, but his final message saved thousands, not just the passengers on the trains that were able to stop before entering the zone of destruction, but also the citizens already in Halifax: The telegram signal reached every operator in the surrounding region, and because of Coleman’s quick thinking, every doctor who felt the earth rumble, up to 160 km away, had almost immediate access to news about what had happened. They rushed in to help. This particular tit-bit at the end of the article is a gem. Times like these tend to also bring the best in some of us.

silasdavis 6y ago
Indeed, thanks, I had missed that after skimming through the filler in that piece. https://en.m.wikipedia.org/wiki/Vince_Coleman_(train_dispatcher) https://en.m.wikipedia.org/wiki/Vince_Coleman_(train_dispatc...
anonu 6y ago
I had trouble understanding exactly how this scenario played out. Interestingly, Wikipedia gave some more color on the timing and distance involved [1]: The death toll could have been worse had it not been for the self-sacrifice of an Intercolonial Railway dispatcher, Patrick Vincent (Vince) Coleman, operating at the railyard about 750 feet (230 m) from Pier 6, where the explosion occurred. He and his co-worker, William Lovett, learned of the dangerous cargo aboard the burning Mont-Blanc from a sailor and began to flee. Coleman remembered that an incoming passenger train from Saint John, New Brunswick, was due to arrive at the railyard within minutes. He returned to his post alone and continued to send out urgent telegraph messages to stop the train. Several variations of the message have been reported, among them this from the Maritime Museum of the Atlantic: "Hold up the train. Ammunition ship afire in harbor making for Pier 6 and will explode. Guess this will be my last message. Good-bye boys." Coleman's message was responsible for bringing all incoming trains around Halifax to a halt. It was heard by other stations all along the Intercolonial Railway, helping railway officials to respond immediately. Also the Wikipedia about Vince Coleman [2] is missing the details from [1]. I guess this is part of the Wikipedia Wormhole people go through... [1] https://en.wikipedia.org/wiki/Halifax_Explosion https://en.wikipedia.org/wiki/Halifax_Explosion [2] https://en.m.wikipedia.org/wiki/Vince_Coleman_(train_dispatcher) https://en.m.wikipedia.org/wiki/Vince_Coleman_(train_dispatc...

amai 6y ago

From a scientific point of view it was unfortunate that no Rapatronic camera was installed in Beirut: https://interestingengineering.com/filming-the-first-milliseconds-of-a-nuclear-explosion-with-the-rapatronic-a-1950-engineering-marvel https://interestingengineering.com/filming-the-first-millise... https://en.wikipedia.org/wiki/Rapatronic_camera https://en.wikipedia.org/wiki/Rapatronic_camera