Zyklon B (IPA: [tsykloːn ˈbeː], also spelle Cyclon B) was the tradename of a cyanide-based insecticide notorious for its use by Nazi Germany against civilians in the gas chambers of Auschwitz and Majdanek during the Holocaust. It consisted of hydrogen cyanide (prussic acid, Blausäure in German, hence B), a stabilizer, and a warning odorant that were impregnated onto various substrates, typically small absorbent pellets, fibre discs, or diatomaceous earth. It was stored in airtight containers; when exposed to air, the material released gaseous hydrogen cyanide (HCN).