Selections and Gas Chambers at Auschwitz-Birkenau

Arrival and Selection Process

Auschwitz gas chambers became the main killing sites of the Holocaust. From 1942 onwards, trains carrying Jews, Roma, and other victims arrived daily at Auschwitz-Birkenau. After stepping off the cattle cars, deportees were lined up on the ramp for “selection.” SS doctors and officers decided within minutes who was considered “fit for work” and who would be sent directly to death. Children, the elderly, mothers with young children, and the sick were almost always directed to the gas chambers. Healthy men and women were sometimes chosen for forced labour, although for most this meant only a short reprieve before death.

Until mid-1944 many transports were unloaded at the so-called Judenrampe between Auschwitz I and Birkenau; after a new railway spur into Birkenau was completed in May 1944, selections increasingly took place on the ramp inside the camp. Selections also occurred inside Birkenau — in barracks and in the camp infirmaries (Reviers) — where registered prisoners deemed “unfit for work” were chosen for gassing.

If you need a site overview, see our guide to the camp layout: Auschwitz map and structure of the complex.

The First Gas Chambers

Before the construction of large crematoria, the SS used improvised facilities:

• In Block 11 of Auschwitz I, the basement was used for early experiments with Zyklon B in September 1941 on Soviet POWs and Polish prisoners.
• In Birkenau, two converted farmhouses known as the “Red House” (Bunker I) and “White House” (Bunker II) were used from 1942 to carry out mass killings.

These sites marked the transition from improvised methods to an industrialised system of extermination. For museum educational materials on deportations, selections, and gassing, see the Auschwitz-Birkenau State Museum’s e-lessons: lekcja.auschwitz.org.

The Gas Chambers and Crematoria II–V

Between March and June 1943, four large crematoria (II–V) were built in Birkenau. Each contained underground undressing rooms, gas chambers disguised as showers, and cremation furnaces built by the German company Topf & Söhne.

• Crematorium II: opened March 1943
• Crematorium III: opened June 1943
• Crematoria IV and V: opened March–April 1943

Zyklon B was introduced differently in these buildings: in Crematoria II–III through openings in the reinforced concrete ceilings; in Crematoria IV–V through wall inlets from the outside. As the Red Army advanced, the SS tried to destroy evidence: Crematorium IV was wrecked during the Sonderkommando uprising on 7 October 1944 and never returned to service; Crematoria II and III were blown up by the SS in January 1945; Crematorium V operated into the final days and was set on fire during the evacuation. For technical context and background, see the USHMM encyclopedia.

Zyklon B — from Disinfection to Mass Murder

Zyklon B was originally a pesticide used to kill lice and prevent typhus. In Auschwitz it was adapted for mass murder:

• Delivered in quantities far exceeding routine disinfection needs.
• Ordered without the warning agent that normally produced a strong smell, so victims would not suspect.
• Supplied by Degesch and Degussa, and distributed by Tesch & Stabenow (Testa).

Executives of Tesch & Stabenow were tried in Hamburg in 1946 and convicted for knowingly supplying Zyklon B for use in gas chambers. More background on gas chambers and Zyklon B: USHMM encyclopedia.

Evidence of Gas Chambers and Zyklon B Use

The existence and function of gas chambers at Auschwitz-Birkenau are confirmed by multiple independent sources:

1. Eyewitness Testimonies — survivors such as Henryk Tauber and Filip Müller described the process in detail; perpetrators, including Rudolf Höss (camp commandant), also provided confessions. See survivor resources at Yad Vashem.
2. Nazi Documentation — blueprints for crematoria, invoices for gas-tight doors, ventilation systems, and correspondence with Topf & Söhne — items unnecessary for ordinary bathhouses.
3. Ruins and Architecture — remains of underground chambers and the physical traces of ceiling or wall openings used to introduce Zyklon B.
4. Chemical Analysis — forensic studies by the Institute of Forensic Research in Kraków (1990s) identified cyanide compounds in samples from gas chamber remains; higher residues were found in delousing facilities, consistent with their repeated use and longer exposure.
5. Allied Aerial Photos — 1944 reconnaissance images show crematoria buildings and columns of people being marched toward them.
6. Post-war Trials — at Nuremberg and later trials in Poland and Germany, SS staff and civilian suppliers were convicted on the basis of converging documentary, material, and testimonial evidence.

Together, these lines of evidence leave no doubt about the use of Zyklon B in the systematic extermination of over one million people at Auschwitz.

Scale of the Crime

Of the roughly 1.3 million deported to Auschwitz, about 1.1 million were murdered. Around 900,000 Jews were killed immediately after selection, sent directly to the gas chambers without ever being registered. The remainder — including Poles, Roma, Soviet POWs, and others — also perished through mass killings, starvation, disease, exhaustion, and executions.

Testimonies and Resistance

Information about mass gassing reached the outside world thanks to prisoners who escaped and reported what they had seen. The Vrba–Wetzler report (Auschwitz Protocols), produced in 1944, was among the first detailed accounts of the extermination process: read more.

Members of the Sonderkommando, forced to operate the crematoria, staged an armed revolt in October 1944, destroying Crematorium IV before being suppressed. Learn more about underground activity and resistance in our overview: Auschwitz resistance.

Legacy and Remembrance

The ruins of gas chambers and crematoria at Birkenau are preserved today as evidence of the Holocaust. Visiting these remains confronts us with the industrial scale of Nazi crimes and the human suffering behind the statistics. It is essential to use accurate language: Auschwitz was a Nazi German concentration and extermination camp in occupied Poland, never a “Polish camp.” If you plan to visit, please review the visiting rules to prepare respectfully. For structured learning, see the museum’s digital lessons: lekcja.auschwitz.org