The English used in this article or section 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.