The Belzec camp is built underground. It is an electric crematorium. There are two halls in the underground buildings. People were taken out of the railway cars into the first hall. Then they were led naked to the second hall. Here the floor resembled an enormous plate. When the crowd of men stood on it, the floor sank deep into a pool of water. The moment the men sank up to their necks, a powerful electric current of millions of volts was passed through, killing them all at once. The floor rose again, and a second electric current was passed through the bodies, burning them until nothing was left of the victims save a few ashes.
Source: The Black Book of Polish Jewry, 1946 (English-language edition), page 313.