Rhinelander, WI – Dangerously high levels of carbon monoxide forced the evacuation of City Hall in Rhinelander Friday morning.

Rhinelander Fire Chief Terry Williams said the 500-parts-per-million reading was the second highest he’s seen in his 25-year career.

The fire department evacuated the building at about 8:30 a.m. A city employee had been showing signs of carbon monoxide poisoning.

The fire department believes the high levels were caused by a problem with the boiler in the building’s basement.