A news article, which you can read in full here, explains how the Nazis made a few changes in the gassing process to streamline the gassing of the Jews. The following quote is from the news article, cited above:
One minor change — call it a “Duh” moment — was to design the gas chamber doors so they opened outward, rather than inwards, because the many dead bodies inside the gas chambers blocked the door’s entrance, making it difficult to push the door inwards. One major design change resulted in locating the gas chambers and the crematoria on the same floor. Previously, the gas chambers had been located in the basement, with the crematoria located on the first floor, necessitating a time-consuming and inefficient transportation of the dead from floor to floor. Putting them on the same floor streamlined the process.
Yes, it’s true. At first, the stupid Nazis had designed gas chambers with both doors opening inward. This was in the gas chamber at the main Auschwitz camp. But where were the gas chambers and the ovens on different floors? The following quote is from the book entitled IBM and the Holocaust in which Edwin Black describes the corpse chute at Buchenwald.
Once the murder decision had been made, all sixteen Jews in the shelf [one row in the barracks] were immediately marched to a small door adjacent to Buchenwald’s incinerator building. The door opened inward, creating a short, three-foot-long corridor. Jews were pushed and herded until they reached the corridor end. There, a hole dropped thirteen feet down a concrete shaft and into the Strangling Room. A camp worker recalled, “As they hit the floor they were garroted … by big SS guards and hung on hooks along the side wall, about 6 1/2 feet above the floor … any that were still struggling were stunned with a wooden mallet … An electric elevator … ran [the corpses] up to the incinerator room [cremation ovens].
As for the doors into the gas chambers opening inward, this is shown in the photo below.
The photo above shows a wooden door into the gas chamber in the main Auschwitz camp. The door opens inward, as you can see. After the Jews were gassed, how did the Nazis get the door open? Don’t worry, there was another door at the other end of the gas chamber. But that door had a glass window, which the Jews could have easily broken. I was told by my Jewish tour guide, in 1998, that an SS man stood outside the door, ready to shoot anyone who broke the glass.
The photo above shows the undressing room for the Krema III gas chamber, which was called Leichenkeller 2 (Corpse Cellar #2) on the blueprint of the building. The victims entered the undressing room by descending the stairs shown in the background in the photo above. Note that the stairs are very short, since the undressing room was only about five feet underground.
To the left in the photo are the steps of the International Monument which is located between Krema II and Krema III at the western end of the Auschwitz-Birkenau camp. The undressing rooms at Auschwitz-Birkenau were only partially underground since the concrete roof over the buildings was three feet above ground.
The crematory ovens in Krema III were on the ground floor with the entrance on the south side of the building. There was a typhus epidemic at Auschwitz-Birkenau in the summer of 1943 and the undressing room could have doubled as a morgue in the event that the bodies piled up faster than they could be burned in the ovens.
The Holocaust victims walked down the steps into the undressing room while an orchestra played classical music. The location of the orchestra was southeast of Krema III, outside the barbed wire enclosure and right next to the soccer field. This was the location where concerts were held for the prisoners while the gassing operation was in progress. The victims were told that they were going to take a shower, after which they would have a nice, hot meal. They took off all their clothing and then proceeded to the end of the long undressing room where there was a door into a Vorraum (vestibule).
The location of the SS entrance, shown in the photo above, was not on the original blueprints for Krema III. Krema III was originally planned to be built at Auschwitz I, the main camp. The original blueprints for Krema II and Krema III called for corpse cellars that were completely underground and included a corpse slide which ended in front of the Leichenkeller doors, but this slide was never built. The SS entrance was built instead, but not in the same location as the originally planned corpse slide.
According to the official version of the Holocaust, which you must believe to stay out of prison in 19 countries, the reinforced concrete roof of Krema III (gas chamber #3) was six inches thick, with four holes, in a zig-zag pattern, where the Zyklon-B gas pellets were poured into the room. These holes were shown on aerial photos taken by the US military in 1944, but they cannot be seen today because the entire roof of Krema III was destroyed when the Nazis blew up the building on January 20, 1945, two days after they had abandoned the camp.
On the left wall of the vestibule was a door into the gas chamber, which was located at a right angle to the undressing room. On the right wall of the vestibule was a door into another anteroom which had an exterior entrance for the SS men. On the back wall of the vestibule was a single elevator which was used to bring the bodies up to the crematory ovens after the victims had been gassed. The ovens and the gas chambers were NOT on the same floor.