In addition to executions by firing squad, other methods of mass murder were implemented for the first time at the hospital in Owińska. Some 400 patients, along with medical staff, were transported to a military fortress in Poznań where, in Fort VII bunkers, they were gassed with carbon monoxide delivered in metal tanks. Other Owińska hospital patients were gassed in sealed trucks by exhaust fumes. The same method was performed in Kochanówek Hospital near Łódź, where 2200 persons were killed between March–August 1940. This was the first successful test of mass murder using gas van poisoning and this technique was later used and perfected on many other psychiatric patients in occupied Poland and Germany. Starting in 1941, gas vans were used on inmates of the extermination camps. The total number of psychiatric patients murdered by the Nazis in occupied Poland between 1939 and 1945 is estimated to be more than 16,000, with an additional 10,000 patients dying of malnutrition and hunger. Additionally, approximately 100 out of 243 members of the Polish Psychiatric Association met the same fate as their patients.