Chełmno extermination camp
Starting in 1941, gas chambers were used at extermination camps in Poland for the mass killing of Jews, Roma, and other victims of the Holocaust. Gas vans were used at the Chełmno extermination camp. The Operation Reinhard extermination camps at Bełżec, Sobibór, and Treblinka used exhaust fumes from stationary diesel engines. In search of more efficient killing methods, the Nazis experimented with using the hydrogen cyanide-based fumigant Zyklon B at the Auschwitz concentration camp. This method was adopted for mass killings at the Auschwitz and Majdanek camps. Up to 6,000 victims were gassed with Zyklon B each day at Auschwitz.