The English used in this article may not be easy for everybody to understand. (October 2017)
HCN is an extremely poisonous chemical, and is lethal in very small doses. A hydrogen cyanide concentration of a few hundred parts per million (ppm) in air can kill a human in less than one hour, and if ingested, it can cause almost immediate death. When high concentrations (of about 5.6%) of the HCN gas is exposed to air, it is also explosive.