From Wikipedia - 'History of Gunpowder....
In 1260, the personal arsenal of Song Dynasty Prime Minister Zhao Nanchong caught fire and exploded, destroying several outlying houses and killing four of his prized pet tigers.[27] The Gui Xin Za Zhi of 1295 records that a much bigger accident took place at Weiyang in 1280, at an arsenal used primarily for the storage of trebuchet-launched bombs:
Formerly the artisan positions were all held by Southerners (i.e., the Chinese). But they engaged in peculation, so they had to be dismissed, and all their jobs were given to Northerners (probably Mongols, or Chinese who had served them). Unfortunately, these men understood nothing of the handling of chemical substances. Suddenly, one day, while sulfur was being ground fine, it burst into flame, then the (stored) fire lances caught fire, and flashed hither and thither like frightened snakes. (At first) the workers thought it was funny, laughing and joking, but after a short time the fire got into the bomb store, and then there was a noise like a volcanic eruption and the howling of a storm at sea. The whole city was terrified, thinking that an army was approaching...Even at a distance of a hundred li, tiles shook and houses trembled...The disturbance lasted a whole day and night. After order had been restored, an inspection was made, and it was found that a hundred men of the guards had been blown to bits, beams and pillars had been cleft asunder or carried away by the force of the explosion to a distance of over ten li. The smooth ground was scooped into craters and trenches more than ten feet deep. Above two hundred families living in the neighborhood were victims of this unexpected disaster.[27]
