The 29-year-old man called for help himself and vomited as he was taken down the stairs and into the ambulance, and eventually died in hospital.
When police interviewed his neighbours, they were told that the hospitalised man had allegedly collected weapons and was believed to have experimented with explosive concoctions.
Worried that he could potentially be a terrorist and that other people in the apartment block might have been exposed to the toxic substance he had drunk, the police were forced to evacuate the property.
A decontamination squad was ordered in and residents were led out wearing face masks. They cleaned the shoes of all the people coming and going from the property, and 14 people were taken away for decontamination treatment.
Firemen also decontaminated the stairway and the ambulance before the all clear was given. Police also carefully checked the flat, accompanied by explosive experts.
Police spokesman Roman Hahslinger confirmed that no weapons or explosives were found in his apartment, adding: "There is no suspicion that there is any connection to terrorism."
The man who died was not named but Hahslinger told the Kronen Zeitung he appeared to have been suicidal, saying: "The man left a farewell letter."
The incident happened in Vienna's Favoriten district when Austria was celebrating its national holiday.
Later, the hospital declared that the substance was not likely to have had any health implications for the remaining residents.
It's thought the man took DNP, a chemical which was used to produce explosives at the beginning of the 20th century but since the 1930s has been used as a weight-loss drug, with severe side effects including death.
It continues to be used by some bodybuilders and athletes to rapidly lose body fat - and has led to a number of accidental fatalities. Vienna firefighter Christian Feiler said that just one gram of the substance can be lethal.
Story courtesy of Central European News.