Here's the way it was in Brescia Italy in the 1700s. They stored 90,000 kg of black powder .The building was hit by lightning .The explosion destroyed 1/6 th of the city , killed 3,000 people .[Wikipedia]
In "Hatcher's Notebook" there is a description and photos of an explosion in NJ at Lake Denmark Nava Depot. BIG !!
And Watson , bring your revolver !