They did this at the vacant lot where the Feringa Building will be erected, behind the physics and chemistry building. The canisters were placed in a hole two metres deep. The EOD then closed up the hole and blew up the substance.
The canisters were found in a lab on Monday. It turned out that they were full of picric acid. In liquid form, picric acid isn’t dangerous. But if the acid is left alone for long enough, it starts crystallising. And that’s when it becomes explosive. The substance is used in tests and experiments, for example as a dye to detect certain metals.
As a precaution, Nijenborgh 4 was evacuated at the behest of the police, after which the university called on the EOD. Access to the building was restored later in the day. The lab containing the canisters remained off limits, however.
It’s not clear how the acid ended up in the lab. Picric acid has been found at educational institutes before. This is how the University of Swansea in the UK cleaned it up two years ago: