Officials Provide Update on Mason City Ammonia Leak, No Injuries Reported

MASON CITY, Iowa — Officials have released additional details following an ammonia leak Saturday evening at a Mason City facility that prompted a large-scale evacuation.

According to a press release from the Mason City Fire Department, crews were dispatched to Crystal Distribution at 633 15th St. SE around 6:08 p.m. on March 21 after a 911 call to the Cerro Gordo County Dispatch Center.

Upon arrival, fire and police personnel confirmed an ammonia release and began evacuating residents in the surrounding area as a precaution. Due to calm wind conditions, the gas spread in multiple directions, forcing responders to expand the evacuation perimeter several times.

The North Iowa Hazmat Response Team was activated, and an Alert Iowa notification was issued to residents, advising them to evacuate.

At approximately 8:50 p.m., hazmat crews located and secured the ammonia shutoff valve, stopping the leak. Air monitoring continued until levels were deemed safe, and at about 9:47 p.m., residents were notified they could return to their homes.

Officials say there were no reported injuries or exposures.

Operations at the facility have been temporarily suspended while an investigation into the cause of the leak continues and any necessary repairs are made.

Multiple agencies assisted in the response, including the Mason City Police Department, North Iowa Hazmat Response Team, Emergency Management Agency, Community Emergency Response Team, and the Mason City Street Department.

The Mason City Fire Department thanked residents for their cooperation and praised the coordinated response efforts of all agencies involved.