Assistant deputy fire chief Bob Martin told CBC News he's never seen anything like it.

Smoke was rising out of the concrete steps on the Forest Hill Road side of the building and the steps were at a temperature of 150 C when emergency crews first arrived, Martin said.

Thermal-imaging cameras were used to monitor the temperature of the steps, which rose from 150°C to 260°C before eventually cooling to 21°C.

Martin said the reaction appears to be linked to an epoxy used to connect a metal rail to the steps when they were constructed more than 40 years ago.

"At that time, they used to use a sulphur base," he said. "They would pour it in a liquid form around that. This liquid base is the part that was on fire — it was in a molten state."

The Fredericton bomb squad was also called in and chemists were being consulted by telephone, Martin said.

A mass spectrometer tested samples against more than 17,000 different chemicals to try to identify the substance that might have caused the reaction.

Concrete has been known to explode under extreme heat, so the gym was evacuated and the nearby road was shut down for about three hours on Wednesday.

Officials still aren't sure exactly what happened, but do not believe the incident was a result of criminal activity, Martin said.

"There's no malice here," he said. "If you're going to cause a disturbance at UNB, why would you choose the back step?"

Officials said they don't expect the reaction to happen anywhere else.

The evacuation order and the road closure were lifted Wednesday afternoon."

Yeah, I don't have too much to say other than perhaps: just who thought a sulphur base was a good idea?  More importantly though: how does something like that suddenly catch fire?  It's not like it's been terribly hot here lately — quite the opposite in fact: cold and rainy with a continuing forecast of cold and rainy.