A blast at the construction site of the Humboldt Forum museum in Berlin has caused damage to the building’s entranceway and left one worker injured. On an otherwise clear blue day, thick black smoke billowed up above the historic museum island on Wednesday morning, where the prestigious, albeit controversial, museum is under construction.

After two vats of molten tar caught fire and engulfed construction materials, some 80 firefighters were dispatched to the site. The fire was quickly brought under control, according to a spokesperson from the museum. Officials are looking into the specific causes of the fire more closely, but it seems that it was not caused by premeditated action.

“Because the tar emitted a lot of smoke, it looked really dangerous but it only caused surface damage to the museum’s façade,” Michael Mathis, a spokesman from the museum tells Artnet News, also confirming that a worker was unfortunately injured from smoke inhalation. He said that the museum’s planned partial opening in September will not be delayed due to the incident. The opening has already been pushed back one year from its original date in fall 2019.

The spokesman added that the global health situation is currently posing a much more considerable threat to the institution’s planned opening, as it has created delays in the delivery of building material, and impacted the workers’ ability to be on the site. Berlin is on lockdown, with most businesses closed, though construction sites are exempt from the ban. A statement from the museum says that officials will be consulting on the progress of the construction work in the second half of April.

“The pictures of the fire above the castle portal scared us all,” German culture minister Monika Grütters says in a statement, expressing her thanks to the actors on site “for being so level-headed and carrying out the evacuation very quickly.”

Set in a rebuilt royal Prussian palace, the Humboldt Forum will host non-European ethnographic collections and an Asian collection. The $700 million development project has ignited fierce debate in Germany on the subject of the restitution of objects acquired during the colonial era. Germany had several colonies in eastern Africa, including Namibia, and the country’s state collections contain Benin Bronzes that are known to have been looted by British soldiers from Benin City, modern-day Nigeria, in 1897.