Pretty much a few vials of Picric acid (TNP) had gone off and crystallised. TNP has a similar structure to TNT, once its crystallised it becomes extremely sensitive to friction, heat and vibration, it can explode at the slightest jolt. Its common for bomb squads to be called to remove and destroy old TNP and TNT. Oh and TNP is common in fireworks because it emits a high pitched tone while burning