Zyklon B is a pesticide. Once exposed to air, Zyklon B releases cyanide; which kills people.

Zyklon-B

Zyklon B was the poison used in the Auschwitz gas chambers.

Because, Zyklon B is a poisonous and toxic gas which will kill people withing 15 minutes

Zyklon-B, an industrial-strength pesticide, was poured through openings in the roofs of the gas chambers. When exposed to air, Zyklon-B gives off a highly toxic gas.

The Allies found millions upon millions of empty Zyklon-B containers when they raided the death camps.

Diesel engine exhausts were also used, either in the "showers" or in gas vans that they transported Jews to the site in.