http://www.jewishvirtuallibrary.org/jso ... ard.html#4
On Wirth's instructions I travel led by truck to Lvov and collected a gassing engine there, which I transported to Sobibor. In Sobibor... [we] unloaded the engine. It was a heavy Russian gasoline engine [probably a tank or train er.gine] with at least 200 h.p. [V-enginel 8 cylinders, water cooled]. We stood the engine on a concrete base and connected the exhaust to the pipe conduit. Then I tried out the engine. To begin with, it did not function. I managed to repair the ignition and the ventils so that the motor finally started. The chemist, whom I already knew from Belzec, entered the gas chamber with a measuring instrument in order to test the gas concentration. Next, an experimental gassing was carried out. I seem to recall that 30-40 women were gassed in one chamber. The Jewesses had to undress on a covered piece of wooded ground near the gas chamber and were driven into the gas chamber by... members of the SS as well as by Ukrainian volunteers. When the women were locked into the gas chamber, I, together with Bauer, operated the engine. Initially the engine idled. We both stood next to the engine and switched from free-exhaust so that the gases were conducted into the chamber. At the suggestion of the chemist, I adjusted the engine to a certain number of revs per minute so that no more gas had to be supplied. After approximately 10 minutes all the women were dead. The chemist and the SS-Fu"hrer gave the signal to switch off the motor. I packed up my tools and saw how the corpses were removed. Transport was by means of a rail-trolley which ran from the gas chamber to a distant area. (StA Dortmund AZ:45 Js 27-61 )