Evacuation of university building was the result of potent mixing agents coming into contact

An emergency evacuation at the Medical Biology Centre at Belfast鈥檚 Queens University last Thursday evening was caused by two potent concrete mixing chemicals somehow coming into direct contact with each other, local media have reported.

The two chemicals - each of which serve as a hardening agent for concrete 鈥� were being used by contractors on the seventh floor of the building, located at the Lisburn road complex.

The subsequent chemical reaction produced a toxic gas that is heavier than air, which drifted down through the building, causing panic among the staff, who were evacuated.

Belfast's Chief Fire Officer Chris Kerr said: "It was a very large operation with 40 officers in breathing apparatus working over a six hour period."

The structure was finally being declared 鈥渟afe鈥� at 23:25 on Thursday.

Queen鈥檚 staff returned to work on Friday, and the university鈥檚 fire officer and safety team have begun an inquiry in to the incident.