On December 8, 1941, the Nazis opened another death camp called Chełmno. At first, they killed prisoners at Chelmno inside vans, using carbon monoxide exhaust fumes. Later, like at the other death camps, the Nazis built gas chambers so they could kill more people at a time. Almost all of the prisoners sent to Chelmno were killed right away. However, the Nazis forced a few strong men into work units called "Sonderkommando". These prisoners were forced to help take dead bodies out of the gas chambers and burn them.