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How Not to Do It: Breaking up Ammonium Nitrate

I’ve come across several odd facts and stories from an old (1927) book called The Romance of Chemistry, given to me in person by Mark Nelson of Frontier Scientific.* Among these is an alarming incident I hadn’t heard about before, one that took place in Oppau, Germany, in 1921. BASF had built a large facility there on the Rhine, and they were running a large Haber-Bosch nitrogen fixation operation. That gives you ammonia, of course, in a reaction that absolutely changed the future of the human race, and it also fed into the Ostwald process (patented in 1902 and still going strong) to oxidize the ammonia and ultimately give you nitric acid. So a Haber-Bosch plant is the perfect place to take nitrogen and oxygen from the air and convert them to huge piles of ammonium nitrate, which is just what had been going on for years in Oppau. There was a lot of ammonium sulfate produced as well, and in practice, the company ended up with a big pile of the mixed salts for sale as fertilizer.

This was exposed to the elements in various ways, and ended up setting up into a giant rocklike mass. So how do you go about breaking that up into pieces that can be loaded out for shipping? Ammonium nitrate (infamously) can be detonated, but hitting it with a pickaxe is not going to be enough. Unfortunately, going after it with pickaxes was not enough for the BASF pile, either. The company conducted tests on the mixed ammonium-nitrate-sulfate salt, and found that it was actually insensitive to detonation. So for the next few years, they broke up the pile, when needed, with dynamite.


Now one has to admit that this sounds insane, prima facie.. And indeed, breaking up a big solid mass of pure ammonium nitrate with dynamite would be a terrible idea, the sort which would only be done once, but the mixed salt passed all the tests, and blowing the fertilizer pile up piece by piece apparently became a regular feature of life at the Oppau plant. It worked fine – until it didn’t. And then it really didn’t work. The photo at right, which is contained in the 1927 book, shows the aftermath. The blast is on the list of the largest non-nuclear manmade explosions, and it did damage in Frankfurt over 50 miles (85 km) away. The damage at the site itself was (as you can see) devastating, and that crater is, as you have guessed, the former site of the fertilizer pile.

Initial reports were confused, as well they might be. Here’s a writeup in Drug & Chemical Markets at the time, full of all sorts of speculation. The initial blame was put on the Haber-Bosch reactors exploding (keep in mind that at the time there was no such plant in the US at all), although you’ll note that the article does mention that a lot of ammonium nitrate was stored at the facility. After a couple of weeks, though, the company stated (in Angewandte Chemie!) that it was definitely not the high-pressure ammonia part of the plant that had blown up, and in fact, that section was still largely intact. From that summary in Nature, it also appears that they were at pains to say that there was certainly no ammonium nitrate present at the plant – no, that would be dangerous, because ammonium nitrate is explosive, you know, and that there was only the robust and well-tested ammonium nitrate sulfate, etc. It turned out, though (as Carl Bosch himself, who was never the same after the disaster, explained) that some (now lower-density) sections of the pile had been filled with material produced under different conditions, and that the explosive nature of the mixed salt could be profoundly altered if the ammonium nitrate concentration were changed. It’s estimated that about 450 tons of the pile detonated, and the blast killed an appalling 561 people, putting it just behind the Texas City disaster as the most deadly ammonium nitrate explosions ever.

If you don’t know the details of the latter 1947 catastrophe, it’s well worth a look, although you should should prepare to have your eyebrows creep up past your hairline in the same way they probably did when you read about that dynamite technique above. I’ll do a whole separate blog post on that one at some point, but imagine workers filling a ship with bags of ammonium nitrate mixture which already felt oddly warm to the touch, and the repeated failed attempts to put out the later autoignition of the now glowing-red cargo hold as the water of the harbor began to boil around it, and you wonder why everyone didn’t just hit the road and continue driving away with their gas pedals jammed against the floorboards. That, by the way, is exactly my recommendation should you ever witness anything similar, although modern industrial safety procedures are largely dedicated to trying to make sure that no one ever does. Lest you think, though, that explosions of ammonium nitrate facilities are a sepia-toned relic, that last link above will show you that every decade since has featured one or more detonations, all the way up to the huge Tianjin explosions in late 2015. Basically, any fire near a storage area for ammonium nitrate should be considered a potential disaster, and the two main options, which have to be weighed against each other depending on ones own situation, would appear to be extinguishing such a blaze as quickly as possible or getting the hell out of the entire vicinity, keeping in mind that said vicinity might have a radius of several miles.

The other lesson from things like the Oppau disaster is that just because something’s been done that way for years does not mean that it’s safe. (Here’s another post on that topic). There are details, there are variables, there are changes that can happen, and especially if you’re working with energetic materials everything has to be looked at carefully. Complacency around such substances can cost you more than anyone is prepared to pay.



*Mark also gave me a no-doubt-valuable Frontier beaker-mug, and while I don’t let swag such as this influence me, of course, I can definitely say that in the same way that Strem is the place you want to buy your palladium catalysts from, Frontier’s boronic acids and other intermediates have never let me down.

38 comments on “How Not to Do It: Breaking up Ammonium Nitrate”

  1. Anon says:

    Meanwhile next door they were breaking up solid piles of dynamite with ammonium nitrate as explosive…

  2. Hap says:

    Perhaps Takata should have paid more attention to this kind of thing…but when people have serious incentives to ignore contrary data, guess what happens.

  3. anon says:

    Wow–the video of the Tianjin explosions is worth a watch

    1. Xiao Bu says:

      Yes, as awful as that disaster was, I could not stop rewatching the video and witness the sheer force captured on video, it never fails to awe. Guaranteed to send chills down your spine.

    2. Dave says:

      Wikipedia says there was 700 tonnes of NaCN at the Tianjin site. I am lost for words.

  4. Earl Boebert says:

    ” just because something’s been done that way for years does not mean that it’s safe.”

    Yup. We used to call that “operational assurance.” The example I used in my teaching was the (probably apocryphal) story that sometime in the 1960s the San Francisco Department of Health decreed that the traditional method for making Peking Duck was unsafe. The head of the Chinese Restaurants Association supposedly replied that they had been doing it that way for 2000 years and nobody had been poisoned yet.

    The problem with operational assurance is that once you change *anything* your assurance level goes to zero, and has to be rebuilt from scratch, either through experience (risky), testing, or analytic methods.

    1. Neil Youngman says:

      Another relevant term might be “normalization of deviance”

      This article talks about normalization of deviance in the context of an aircraft crash.

      I believe normalization of deviance was relevant to the Deepwater Horizon as well.

      1. Calli Arcale says:

        Yeah, normalization of deviance is a very insidious thing. It was a major factor in the Columbia (STS-107) accident as well. Foam shedding from the External Tank had been forbidden since day one, but had occurred on every single launch (and occurred on every single launch subsequently) because it just wasn’t a realistic requirement. Over time, the fact that it had never struck a critical component of the Orbiter gave false reassurance that it never would, even after one particularly close shave when Atlantis came back with severe tile damage frighteningly close to one of main landing gear doors. It hadn’t been fatal, so increasingly it came to be seen largely from the perspective of how much effort it took to repair the damage each time there was a foam strike. Nobody dreamed it could be fatal. Until it was.

    2. Jewels says:

      I see Calli Arcale already brought up the Columbia incident re: normalization of deviance, but it was also an issue with Challenger. Diane Vaughan wrote a book on it in 1997, actually. “The Challenger Launch Decision: Risky Technology, Culture, and Deviance at NASA”.

      Now, I’m *far* more familiar with the Columbia tragedy and the lead-up to what happened. (If anyone’s interested, “Comm Check: The last flight of the shuttle Columbia” does a great job with all the details.) So I can’t vouch for this as absolute fact. But I’ve read that there were other “leaks” in the boosters before Challenger. None so dramatic or in just the wrong place, but they apparently had happened. There certainly were known issues with the O-rings since the mid-70s.

      (It was also true to a lesser degree with the Apollo 1 fire. In the case of Apollo, it hadn’t flown yet, but everyone *knew* there were big problems with the Block 1 command module. Gus Grissom actually hung a literal lemon from his yard on the capsule a week before the fire to express his opinion of it. (Grissom had been part of the engineering team in building the Mercury and Gemini capsules, but Apollo was already being built when he got into the program. Yet NASA had flown all the Mercury and Gemini missions without anyone dying – although it was a *very* close thing with Neal Armstrong and Dave Scott in Gemini 8. They had Kennedy’s “end of the decade” deadline to meet though, so they kept going, pretending it was all good…until it suddenly wasn’t “all good”.)

  5. Kevin Sours says:

    Modern safety procedures are generally good. Enforcement of modern safety procedures leaves something to be desired.

  6. myma says:

    I don’t think I will ever read that book, that is if I could ever find a book from 1927 anyway. Just seeing the picture was enough. Baboom.

  7. M. Welinder says:

    > Modern safety procedures are generally good.

    Well, yes and no. “Zoning” would be such a procedure, but I don’t think Texas has figured that out yet.

  8. Tom says:

    The linked speech from Carl Bosch is quite something. Not many CEOs today who could honestly say this of a plant:

    “For me personally, who built the Oppau factory, the task is doubly difficult, since this tragedy concerns my life-work to which I cling with every fibre of my being and whose development 1 have watched from the very start, together with my fellow-workers who have stood by me loyally in joy and sorrow throughout the long years of its growth.”

  9. Anon says:

    You met Mark Nelson in person? He is an expert in tetracyclines and invented Omadacycline from scratch in Chinatown, Boston while at Paratek Pharmaceuticals in Boston. Great guy, good scientist who trained many of us in the field making those crazy antibiotics. He told me once that Streptomyces soil bacteria talked to him, telling him and his Somalian Super-Scientist Mohamed Ismail how to modify the structure to come up with new ones. That was after a couple of beers at Jacob Wirth’s up the street though.

    His stories about antibiotic discovery are legendary and I hear he is writing a book about the antibiotic industry called “They Eat Their Own” . THAT will be a good read!

    1. S.O'B says:

      Nice throwback!

  10. Anonymous Researcher snaw says:

    My grandfather was a fireman, and at the time of the Texas City Disaster was in charge of the fire brigade at a shipyard East of Texas City. In fact, he was on his way to Texas City to help them deal with that fire when it went boom. According to my father, had the bang occurred about half an hour later than it did, my grandfather would probably have been one of those who got blown up.

  11. metaphysician says:

    I know you say you’ll do a separate article on the Texas City disaster, but I have to ask. Why *were* the bags already exotherming before they were even loaded aboard? Some quick googling on my part didn’t turn up any explanation. I mean, ammonium nitrate isn’t normally that unstable, I wouldn’t expect autoignition to be an issue unless something has gone really wrong.

    1. AndrewD says:

      One explanation for the Exotherm, was that the prilled ammonium nitrate had been wax coated to reduce its hygroscopic nature. Unfortunately this resulted in a product akin to an Ammonium Nitrate Fuel Explosive which began a slow decomposition. This may be apocryphal.

  12. MCS says:

    Add West, Texas to the list, about 250 tons, a little more than 2 rail cars. Dry fertilizers are usually stored in wooden buildings because of corrosion.

    Then there’s WIPP where Los Alimos substituted cellulose for clay absorbant and made gun cotton by mixing it with nitric acid. Radio active gun cotton.

  13. Kaleberg says:

    I read about Oppau in Smil’s ‘Enriching the Earth’. I got the impression that Bosch died of a broken heart during World War II.

  14. Istvan Ujvary says:

    The Oppau-incident and relevant safety issues were discussed in detail during our course “The Chemical Factory” (‘Vegyigyár’ in Hungarian), thought at the Budapest Technical University in the mid-1970s when I was studying chemical engineering. This was before Seveso and Bhopal (which I visited while in India in 2003). If I recall correctly, one of the safety precautionary measures was about ‘critical mass’: do not pile up dangerous chemicals on one location.

    1. Anonymous says:

      Sorry to be lazy and not look up details myself, but I seem to recall that the Bhopal plant was originally constructed with a large, legally required buffer zone between the plant and populated areas. As the population grew, people and their dwellings encroached upon the plant, eventually with shanties built right up against the outer fences of the plant. The people couldn’t be removed or displaced because they had no place else to go. (One law mandated a buffer zone; another law said that people couldn’t be removed.) The plant was still a poorly maintained safety hazard, but there would have been fewer injuries if people were not residing inside the buffer zone. … I’m not defending Dow. I’m just thinking that fertilizers and pesticides helped to spur population growth but there was no healthy or safe place to put the growing population.

      1. Istvan Ujvary says:

        Yes, indeed. Before leaving for India, I read the excellent, and I would say balanced, book by Dominique Lapierre & Javier Moro describing all factors contributing to the unprecedented disaster in detail:

      2. Anonymous says:

        It was Union Carbide, not Dow. Basically ended the company.

    2. milkshaken says:

      I bet they did not tell you that few years before Seveso a runaway reactor with 2,4,5-trichlorophenol blew up in Spolana Neratovice, under very similar circumstances, resulting in massive dioxin contamination, which put out of business a facility producing crappy 2,4,5-T exported to US market (and there being “repackaged” into Agent Orange). Czech-made Agent Orange ingredient was cheap but contained atrocious levels of dioxines because trichlorophenol came from alkaline hydrolysis of waste stream of HCH isomers.

  15. milkshaken says:

    Ammonium nitrate + Haber-Bosh plant = double whammy: when it goes boom all that compressed liquid anhydrous ammonia in storage tanks likely gets out – on hundred ton scale – and since liq. NH3 boil-off is highly endothermic it takes surprisingly long time to evaporate; the disaster area remains gassed with ammonia for many hours…

  16. Morten G says:

    So wetting/dissolution of ammonium nitrate is an endothermic reaction (and used in cold wraps) but is the drying of ammonium nitrate significantly exothermic? I’m not enough of a chemist to figure that out.

  17. aairfccha says:

    Another Ammonium Nitrate explosion happened on a smaller scale in 2004 – maybe. At least that’s the official story behind the Ryongchŏn disaster.

  18. Mark Thorson says:

    I’m reminded of a curious incident mentioned in a century-old book on carbon black. It mentioned that a customer reported receiving a shipment with an empty barrel. Back in those days, carbon black was shipped in wooden barrels with paper linings. On inspection, it was concluded that somehow the carbon black in that barrel had ignited and burned very slowly until it was almost completely gone. The paper lining was barely singed.

  19. Martin F says:

    My hometown is no. 1 on the list of explosions of wikipedia! And I can confirm that they still talk about “the great explosion” there. The most notable thing I know about it is it blew the medieval church spire off of the church which is about 4 miles away glad I wasn’t there to see it live! My friends family actually owns the farm that now sits on the site of the factory which thankfully no longer exists…

  20. Vader says:

    “Then there’s WIPP where Los Alimos substituted cellulose for clay absorbant and made gun cotton by mixing it with nitric acid. Radio active gun cotton.”

    Some details, which I can’t verify but sound perfectly plausible, and which you absolutely didn’t hear from me, on how this happened:

    There was incredible pressure to meet deadlines on shipping waste to WIPP. A scientist/manager dictated a memo to his secretary outlining the procedure.

    He said “Inorganic kitty litter will be used as an absorbent.” Meaning, clay-based kitty litter, which would indeed have been a reasonable and cost-effective absorbent for nitrate waste.

    But the secretary heard “An organic kitty litter will be used as an absorbent.”

    The memo was apparently not proof-read by the scientist/manager, or at least not carefully, in the rush to meet the deadline. The mistake slipped through. The technicians reading the instructions scratched their heads, because this really didn’t sound right, but it was there in the instructions from On High. In went the cellulose-based kitty litter.

    FWIW, the release of radioactive material from the resulting explosion was negligible, but with radioactive material, that doesn’t much matter.

  21. Mike Andrews says:

    I grew up not far from Texas City, and we used to drive through it (past, inter alia, a tin smelter and a SiC furnace facility) to get to the beach at Freeport. The Grandcamp’s 2-ton anchor was blown > 1.5 miles, and its multi ton propeller a similar distance. Sobering.

  22. Gordonjcp says:

    I always reckoned that back home when we buy in ammonium nitrate (in 1-tonne bags, several of them) we probably shouldn’t store it so near the 200-litre barrels of tractor diesel.

    1. Derek Lowe says:

      Jaysus. No, that’s a pretty good idea. Those bags get even heavier when they’re soaked in diesel.

      1. Yazeran says:

        On the other hand once soaked in diesel you do not have that pesky problem with the bags getting even heavier with absorbed water if they get wet….. *evil grin*

      2. Dave says:

        And diesel-soaked ammonium nitrate isn’t much use as fertiliser 🙂

  23. GladToMoveToProcess says:

    I remember the same photo, with the ammonium nitrate explanation, in one of my parents’ college intro chem texts from the 1930s. That image comes to mind whenever, happily rarely, I have to work with the stuff.

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