A true monument to human error. They used a tanker to ship bulk quantity of diesel fuel and ammonia nitrate on the same boat, in order to save the cost of shipping it on two boats. The tanker had two 20,000 bbl tanks filled with diesel fuel, and tons of nitrate in 50lb paper sacks stacked up in the space between the tanks, one of which sprung a leak, soaking the nitrate for hours. You could not have built a better bomb on purpose.