Around 4:25 p.m. on Wednesday, following an explosion and anhydrous ammonia leak at CF Industries, officials asked residents of Yazoo City to shelter in place, with a plume of orange ammonia billowing into the sky. By 12:30 a.m. that night, the shelter in place order was lifted. No deaths or injuries have been reported as a result of the incident.
The plant produces hydrogen and nitrogen products, including ammonia and fertilizer. CF Industries said in a statement that “all employees and contractors on site at the time of the incident have been safely accounted for.”
While most residents were told to shelter in place, some were ordered to evacuate Wednesday, including at a nearby Walmart.
“The only roads (that) need to be evacuating is Generette and Renshaw Road,” the Yazoo County Sheriff’s Office wrote in a Facebook post late Wednesday. “All businesses north of 15th street have been evacuated. All residents are encouraged to shelter in place only.”
Today, Scott Simmons, director of external affairs at the Mississippi Emergency Management Agency, told the Mississippi Free Press that the emergency was over and residents could continue about their business: traffic controls near the plant were lifted Thursday morning at 8 a.m.
“CF Industries has their own team on site working with state investigators to determine the cause of the event,” Simmons said. “MDEQ continues to conduct air monitoring tasks to ensure there’s no impact. Today, there’s none.”
MEMA Monitoring Air Contamination
Anhydrous ammonia is a pure compound of nitrogen and hydrogen atoms, usually stored as a compressed liquid. It’s a critical component of modern farming and one of the most common methods of crop fertilization, but also an extremely dangerous substance requiring careful handling and storage.
Wednesday night, Simmons told the Mississippi Free Press that “air monitoring results (near the plant) were 25 ppm,” or parts per million, a measure of how concentrated a substance is in the air. Simmons confirmed that traffic control points have been established in the area “at Highway 49 East at Generette Road to divert traffic southbound, Highway 49 at Willie Morris Road to divert northbound, Highway 49 West at the Highway 3 interchange to divert southbound traffic and Highway 3 North at the 49W interchange to divert southbound traffic.”
The National Institute for Occupational Safety and Health considers 25 ppm of ammonia the limit for “the maximum airborne concentration below which nearly all individuals could be exposed for up to 1 hour without experiencing more than mild, transient adverse health effects or without perceiving a clearly defined objectionable odor.” Just 300 to 500 ppm is considered the “maximum short exposure tolerance.”
Direct exposure to concentrated anhydrous ammonia is dangerous or fatal. Direct contact with skin causes “reduction to a sticky, gooey substance as the chemical burn progresses,” the North Dakota State University Fargo Extension says. “Skin that is chemically burned by the ammonia actually is killed and is not capable of healing or replacing itself. Damaged tissue must be removed surgically so that healing can proceed. The results often are disfiguring.”
Breathing in anhydrous ammonia in high concentrations can cause caustic burns and permanent damage to the lungs.
Unlike ammonium nitrate, which is an extraordinarily explosive chemical and the cause of some of the worst industrial explosions in history (including the 2020 port explosion in Beirut, which killed 218 people), anhydrous ammonia lacks an oxidizer and is thus less explosive. But anhydrous ammonia is highly volatile, stored in heavily pressurized tanks, and is susceptible to “boiling liquid-expanding vapor explosions” or BLEVEs.
Anhydrous ammonia at typical atmospheric pressure boils at -28 degrees Fahrenheit, meaning exposed liquid ammonia at regular temperatures will immediately flash-boil into a gas, massively expanding into a plume of dangerous vapor. Safely stored in heavily pressurized tanks, that same ammonia can maintain its dense liquid form at significantly higher temperatures.
As of Wednesday evening, Simmons could not confirm if the accident at CF Industries was a BLEVE, caused by tank failure, or the result of another type of explosion or incident.
Red Cross Opens Reception Center
The American Red Cross opened a reception center to provide a climate-controlled environment for residents who need temporary assistance or are unable to remain in their homes. The center is at Yazoo County High School at 191 Panther Drive, Yazoo City, MS 39194.
“Red Cross volunteers are on-site to offer comfort, information and support,” a Red Cross announcement says.
Mississippi Gov. Tate Reeves said on Wednesday evening that the Mississippi Emergency Management Agency, the Mississippi Department of Environmental Quality and the Mississippi Department of Public Safety are assisting local emergency managers.
“Initial reports indicate the leak is due to an explosion. At this time, no deaths or injuries have been reported,” Reeves said.
The Red Cross said that air quality monitoring and hazardous material teams “are actively assessing the situation.”
The organization urgesdresidents who come to the center to bring essential items, including perscription medications and medical supplies; important documents like IDs and insurance; personal hygeine items; cell phone chargers; and comfort items for children if needed.