A chemical spill at Unity Health Insurance's Sauk City office building Wednesday afternoon led to the evacuation of the company's entire 140-employee workforce and forced 39 employees to be transported to Sauk Prairie Memorial Hospital for precautionary purposes.

At about 1 p.m., Sauk Prairie police were called to Unity to investigate a chlorine-bromine chemical spill in the building's mechanical room, said Sauk Prairie Police Chief Jerry Strunz.

There was some concern at the scene that the chemicals may have made it into the facility's ventilation system and were spread throughout the office building.

Almost 40 employees were taken to the hospital after they displayed symptoms of exposure to the chemicals, which included respiratory issues and burning of the eyes.

The Sauk Prairie Ambulance Service arranged for a local bus service to take 22 of the victims from the scene to Sauk Prairie Memorial Hospital. Seventeen other victims were taken by ambulance to the hospital. Police cordoned off Carolina Avenue in front of the office building between Dallas Street and Business Drive to set up a stanging area and evacuees not taken to the hospital were provided water to stave off the afternoon heat.

No one was seriously injured as a result of the chemical spill and all of the patients transported to the hospital have since been released, according to a statement posted on the Sauk Prairie Memorial Hospital Web site.

Strunz said the chlorine-bromine solution that spilled was a "very diluted version," adding that unless a person were to come in direct contact with it, the symptoms were uncomfortable but not life-threatening. Exposure to the chemical was limited to those inside the building at the time of the incident.

Chlorine-bromine is a biocide used in air conditioning systems to kill mold and similar substances that are detrimental to the system's operation.

As of 4:30 p.m., the Sauk City Fire Department still was cleaning the spill, though evacuated employees were allowed to return to the parking lot to retrieve their vehicles and Carolina Street has been reopened to traffic.

Strunz said he expects employees will be able to return to work as normal at the office building Thursday morning. He said it was not known what caused the spill, though a cleaning process that took place at Unity earlier in the day may have played a role.

"The investigation into that is obviously still progressing," he said, adding that the initial concern was to respond to the spill and now that the spill has been cleaned efforts will transition to the investigation.

Shortly after 1:30 p.m., Sauk Prairie Memorial Hospital declared an emergency in order to respond to a "disaster situation" at Unity and locked down the hospital, effectively closing it to anyone not directly affected by the spill or responding to it. According to the hospital's Web site, the hospital officially ended the lockdown and resumed normal operations at 3:25 p.m.

"Beginning at 1:50 pm, 30 individuals from Unity Health Insurance of Sauk City were accepted into SPMHC's Emergency Room and treated for respiratory symptoms and burning eyes as a result of exposure to fumes from a chlorine-based cleaning solution," according to a statement on the hospital's Web site, www.spmh.org. "Hospital staff and local physicians responded to treat patients. Everyone has been treated and released and advised of signs and symptoms to watch for." 

The Baraboo Ambulance Service was also called to the scene to provide backup assistance for the Sauk Prairie Ambulance Service.

Unity is located in the Sauk City Industrial Park south of Meyer Oak Grove, a park off Highway 12 in Sauk City.

According to its Web site, Unity Health Insurance is an affiliate of UW Health and markets its products and services to 20 counties in southwestern and southcentral Wisconsin. Formed in 1994, Unity is a primary provider of health insurance for the University of Wisconsin system and is a wholly-owned subsidiary of University Health Care, Inc., an affiliate of the Univeristy of Wisconsin Hospital and Clinics and the University of Wisconsin Medical Foundation. US News & World Report ranked Unity as the no. 24 health insurance company in the United States in 2008.