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.