Hydrogen cyanide (HCN), also called prussic acid, is a bitter-smelling and potently toxic liquid chemical compound whose molecules consist of one atom each of hydrogen, carbon, and nitrogen. It is useful in chemistry and has applications in plastics, mining, pharmaceuticals, and biotechnology. However, its flammable and poisonous nature makes it extremely dangerous; it boils into a gas at slightly above room temperature, and at concentrations of two hundred parts per million it can kill a human in under an hour. At concentrations of two thousand parts per million, it is lethal in less than one minute. At concentrations of 5.6% it will readily combust and explode, but at that point it will have already killed everything in the vicinity.
