The Silvertown plant had actually stopped making Caustic soda about five years before the fire. As demand for Caustic Soda had waned the demand for munitions had waxed, so the plant was repurposed to make TNT. By January 1917 the plant was producing TNT for Brittan’s effort in World War I at full bore. This amounted to about 9 tons of TNT per day. On the 19th the plant had a little over five-days of production waiting in railroad cars to be shipped out.
Due to the time of day few people were at work. Unfortunately, due to the urban location of the plant, when the 6:52 explosion took out many nearby buildings (like the fire station) it resulted in 73 deaths. Molten metal from the railway cars that had contained much of the TNT rained down on many flammable surfaces. One chunk hit a tank holding 200,000 cubic meters of natural gas which exploded in a spectacular fireball. The explosions at Silvertown were reportedly seen as far as 100 miles away.
The year before, on April 2nd 1916, 200 tons of TNT vaporized a plant in Uplees (near Faversham). 105 people were killed. What fragments they could find of them were buried in a mass grave in the Faversham cemetery.
The vacuum process used at the Silvertown plant was invented by Brunner Mond chief chemist F. A. Freeth who described it as:
“Manifestly very dangerous.”It was early in WWI when Freeth, who had been fighting in the trenches in France for six weeks, received an urgent plea to return to England. It had been discovered that the Germans had scaled-up a process for making explosives from air and coal. The TNT process that the allies used would soon lag behind this new German process enough to give Germany an overwhelming advantage on the battlefield. The allies wanted to cut their TNT with inorganic nitrates (which was almost as explosive as pure TNT) to avoid losing the war. Freeth was the best chemical engineer to scale the process up with an eye towards product rather than safety.
It took Freeth three days to effectively solve the scale-up problem.
Establishing the process required political as well as engineering skills. Glitches and hiccups in converting soda-ash factories to the nitrate-cutting process caused long down-times early-on. In the middle of one of the stoppages a gaggle of French generals announced they were going to tour the factories whose process was to stave-off their imminent defeat. Freeth devised a complicated shell-game to prove to the French generals that the process was working.
Freeth unpacked as much product as he had on hand, and charged the factory with it. He placed a lookout on a bridge the generals would traverse on the way to the plant, and when the lookout signaled their approach Freeth turned the factory’s machines on. For the next 10 minutes, under the gaze of the French generals, he “produced” the nitrate-cut TNT. Minutes after they walked out the door the machines, having run dry of material to work, stopped.
"At the end of every month we used to write to Silvertown to say that their plant would go up sooner or later, and we were told that it was worth the risk to get the TNT." -- Francis Arthur Freeth
The year after the Silvertown explosion, on 1 July 1918, eight tons of TNT took out a substantial part of the National Shell Filling Factory in Chilwell. Of the 137 people killed in Chilwell only 32 could be positively identified. The rest were buried in a mass grave in the Attenborough churchyard.