But as the 'critical time' which was mentioned in the threatening letter passed, nothing happened.
"There have been a number of letters sent to the police recently," said Blekinge police spokesman Thomas Pärlklo late on Tuesday morning.
"Someone is threatening to let off explosives in the building."
In total, there have been eight or nine letters which seem to have been sent by the same person.
The latest letter was taken extremely seriously by the police, who decided to keep people away from the building all morning.
Thomas Pärlklo declined to comment on the possible motives of the person behind the letters.
The building which was the subject of the threat is usually used for staff training and is on the Institute's Gräsvik campus.
Security has been increased in the building while police try to identify the perpetrator of the threats.