As you asked the same question twice I will give you the same answer twice.
Fred Leuchter was called as a witness in a Canadian court case to "prove" that the Holocaust never happened.
His credentials were that he held a degree and was an expert in the design of Gas chambers of which he had designed several for the US Penal system for the execution of inmates.
On further examination it would appear that Mr Leuchter had a degree (a poor one) in History. How this qualifies you as an engineer I am still not sure.
People that he claimed to have worked on Gas chambers for the US Penal system are quoted here.
Leuchters report was based mainly on the lack of Cyanide compounds found in "scrapings" from the walls of the gas chambers.
These scrapings were actually a single brick which he took from a gas chamber which had been in the open air for 45 years, ground up and then presented to the Institute forForensice research at Krakow. The Institute found almost Zero Cyanidic compounds. Hydrogen cyanidic compounds exposed to weather have a half life of approximately 4 days. After 45 years it would be amazing if a SURFACE scraping showed any significant % of cyanide let alone a whole brick ground up into powder
Once the institute realised exactly what it had been presented with it stated that its findings could not be considered accurate. It then conducted its own tests which are presented here.
Various people claim that Zyklon B always leaves prussian Blue stains because the delousing sheds at Auschwitz are covered in it. This is True. they are.
To kill humans with hydrogen cyanide gas takes a concentration of 315 parts per million (PPM) for a time of around 10 minutes.
To kill lice takes a concentration of around 16,000 for up to 72 hours.
This is why there is visible Prussian blue in the delousing chambers which have not been exposed to the elements. A concentration 48 times stronger and an exposure time of 288 times longer and the walls were not hosed down between treatments to get rid of the excrement.
Now do you have any more BS "proof" that the Holocaust did not happen?