Phosphorus night bombing during the First World War. Soldier silhouetted against exploding phosphorus incendiary bombs during a night-time attack at Gondrecourt-le-Chateau, France, during the First World War. The white phosphorus form of the element is highly flammable in air and toxic. Once it starts burning, it is difficult to extinguish. It it comes into contact with human skin it can cause severe burns that are difficult to treat. This United States Army Signal Corps photograph was taken on 15 August 1918.