MASON CITY — A hazardous ammonia leak at a local distribution facility prompted a large-scale evacuation in southeast Mason City on Saturday evening, March 21, 2026.
The Mason City Fire Department was dispatched to Crystal Distribution, located at 633 15th St. SE, at approximately 6:08 PM after a 911 call reported the release of ammonia gas. Upon arrival, emergency responders confirmed the leak and immediately began evacuating nearby residents. Due to extremely calm wind conditions, the ammonia cloud did not dissipate quickly and instead spread outward in multiple directions. This forced fire and police personnel to expand the evacuation perimeter several times throughout the evening to ensure public safety.
The North Iowa Hazmat Response Team was activated to manage the scene, and an Alert Iowa notification was broadcast to residents between 12th Street SE and 19th Street SE, advising them to leave their homes. Hazmat personnel successfully located and secured a shutoff valve at approximately 8:50 PM, effectively stopping the release. Crews remained on-site to monitor air quality until ammonia levels were deemed safe for the public to return.
At 9:47 PM, officials issued an all-clear notification, informing residents they could safely re-enter the area. Cerro Gordo County Emergency Management officials have advised anyone noticing lingering odors to ventilate their homes using fans and open windows.
There were no injuries or medical exposures reported in connection with the incident. Operations at Crystal Distribution have been temporarily suspended while facility staff and investigators work to determine the exact cause of the leak. Assisting agencies included the Mason City Police Department, the Emergency Management Agency (EMA), the Community Emergency Response Team (CERT), and the Mason City Street Department.