Haber defended gas warfare against accusations that it was inhumane, saying that death was death, by whatever means it was inflicted and referred to history: "The disapproval that the knight had for the man with the firearm is repeated in the soldier who shoots with steel bullets towards the man who confronts him with chemical weapons. [...] The gas weapons are not at all more cruel than the flying iron pieces; on the contrary, the fraction of fatal gas diseases is comparatively smaller, the mutilations are missing". During the 1920s, scientists working at his institute developed the cyanide gas formulation Zyklon A, which was used as an insecticide, especially as a fumigant in grain stores.