Weddings can cause stress, but they probably should not be posing health risks.

More than two dozen guests attending a wedding reception Saturday in Madison, Wis. were taken to the hospital to be treated for carbon monoxide poisoning. The wedding reception took place at Salon Centinela, an indoor soccer club, in Madison’s East Side. 

The Wisconsin State Journal reported that emergency personnel were called to the indoor club when a guest fainted during the reception. Once an emergency crew arrived, other guests complained about feeling unwell, and many reported a strange, noxious smell within the facility. The source of the fumes was said to come from a generator that was running indoors for the reception’s band.

Firefighters detected carbon monoxide just near the entryway of the building using handheld air monitors which, “peaked at 405 parts per million in the center of the building,” reported CBS 58.

The indoor generator was immediately removed and the building firefighters ventilated the facility.

Firefighters evacuated the building, which included some 300 wedding guests. At least 26 people, who suffered from headaches, nausea and dizziness, were taken by ambulance to UW Hospital East. Other guests were received as walk-ins at other nearby hospital locations, according to Wisconsin Radio Station WTMJ.

All patients were said to be alert and stable, and all were expected to fully recover.

Cynthia Schuster, a spokeswoman for the Madison Fire Department, spoke of the inherent dangers of fuel-powered equipment used in doors. “Carbon Monoxide is a known byproduct of this equipment, and it quickly becomes deadly when the odorless gas accumulated a in a closed space,” she told The Wisconsin State Journal.

The Center for Disease Control and Prevention (CDC) published a report that stated that a total of 5,149 deaths were reported from unintentional carbon monoxide poisoning in the United States between 1999 and 2010. That averaged out to 430 deaths per year in the U.S.