You seem to be asking a question about one of the six death camps built by the Nazis, named Chelmo in Poland. (Yes, there were many other camps, but there were six camps whose sole purpose was to murder Jews and other Nazi enemies, i.e they were not work camps etc..)
Please see the link below.
5,000 gypsies died at Chelmno.
Routine gassings at Chelmno started on 8 December 1941.
The sole purpose of Chelmno was extermination by gassing in closed vans.
The extermination camp Chelmno was located near Chełmno nad Nerem; in Poland.
Their was 4 big ones and 1 little barracks in Chelmno.
Chelmno was an extermination camp. There are only two known survivors.
Yes, Chelmno (Chełmno) is located in the Kuyavian-Pomeranian Voivodeship in northern Poland.
Chelmno The extermination camp operated from December 1941 till March 1943.
It is said around 152,000 people perished in Chelmno. There have been only 2 known survivors.
There were only two (!) known survivors from Chelmno ... They are both dead now, so the answer to the question is none.
Nope
Chelmno