The Port Neal fertilizer plant explosion occurred on December 13, 1994 in the
ammonium nitrate
Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...
plant at the Terra International, Inc., Port Neal Complex, south of
Sioux City, Iowa
Sioux City () is a city in Woodbury and Plymouth counties in the northwestern part of the U.S. state of Iowa. The population was 85,797 in the 2020 census, making it the fourth-largest city in Iowa. The bulk of the city is in Woodbury County ...
, United States.
[ Four workers at the plant were killed by the explosion, and eighteen others were injured. The seven-story building at the seat of the blast was completely destroyed, leaving only a crater, and significant damage was inflicted to the surrounding structures.]Nebraska
Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the sout ...
. Two 15,000-ton refrigerated ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
storage tanks were ruptured, releasing liquid ammonia and ammonia vapors which forced the evacuation of 1,700 residents from the surrounding area.
Causes of accident
An investigation conducted by the United States Environmental Protection Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...
(EPA) concluded in 1996 that the explosion was initiated by an accelerated thermal decomposition reaction as "a direct result of unsafe operating procedures and conditions" at the plant. The investigation team concluded that the explosion resulted from a lack of written, safe operation procedures at the Terra Port Neal ammonium nitrate plant. The lack of safe operating procedures resulted in conditions in the plant that were necessary for the explosion to occur. The significant conditions that caused the explosion were:[
1. Strongly acidic conditions in the neutralizer and rundown tank;
2. Prolonged application of 200 psig steam to the neutralizer nitric acid spargers;
3. The creation of bubbles and low density zones in the neutralizer;
4. Lack of flow in the neutralizer and rundown tank;
5. The presence of chlorides, from a cooling water leak, in the neutralizer and rundown tank;
6. Lack of monitoring of the ammonium nitrate plant after the plant was shut down with the
process vessels charged.
The EPA had conducted a safety audit at the plant just eight months prior to the explosion. The plant was Iowa's largest producer of nitrogen-based ]fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s and its loss contributed to a national 50% increase in the cost of fertilizer by the following year.
See also
* Ammonium nitrate disasters
References
{{Ammonium nitrate disasters
Explosions in 1994
1994 industrial disasters
1994 disasters in the United States
Disasters in Iowa
1994 in Iowa
Woodbury County, Iowa
Fertilizer companies of the United States
Industrial fires and explosions in the United States
December 1994 events in the United States
Ammonium nitrate disasters