What They Were
The Nazi's way of exterminating anyone they deemed as "unworthy of living". They told the future victims that they were going to get disinfected in a shower. Believing this, they went into the chambers, some forced and others with no hesitation, and were then locked in with no air to breathe. Nazi's would pack as many people as they could into the chamber until there was no possible way to fit another person. Depending on the strength of the gas, the Jews and other victims would be dead within 3 to 30 minutes roughly, gasping and struggling for air in the process. The more people that were in the Chambers, the quicker they would die as well. After the Jews would be dead, or just about there, Nazi's would take the corpses and either throw them in pool sized pits and bury them, or burn the corpses for a "quicker clean up". In just Auschwitz, roughly 6,000 Jews were killed a day in gas chambers. Unfortunately this was a very popular and one of the most torturous way to exterminate the Jews and was used until the end of the Holocaust.
This an example of one of the gas chambers used during the Holocaust. As you can see, they are very small, as well as a very uninviting and slightly disturbing atmosphere. Gas would be thrown in from the side port hole by a Nazi and the rest would be taken care of from there.
Here is a picture of Hydrogen Cyanide, a common gas used during the Holocaust. It would be stored in a container and when the time came, it would be opened and the pellets would be thrown into the chamber. They would then let off a toxic gas that would cause Jews to suffocate and then kill them very quickly.
In the video above, it gives a quick tour of the inside of a gas chamber in Auschwitz. It gives a very clear tour of the path that the Jews took right before they died and the last things they saw. It gives a great example of what it was like to be in their shoes.