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"Lessons Learned" is a series of drop-in articles prepared by the NTSB for use 
in publications of other organizations.  An index of articles is available at
http://www.ntsb.gov/events/journalist/lessons/lessons.htm
05/2005
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Lessons Learned from Accident Investigations 
Farm Cooperatives Urged to Review Emergency Procedures 

The deadly release of anhydrous ammonia following a nurse tank rupture in Iowa has 
prompted safety officials to urge farm cooperatives to review their emergency procedures 
to avoid deaths and injuries. 

The National Transportation Safety Board (NTSB) became concerned about emergency 
preparedness during its investigation into an April 2003 accident in Calamus, Iowa, 
which occurred at the River Valley Cooperative. Two loaders filled a nurse tank with 
anhydrous ammonia at a tank filling facility. As the loaders were preparing to connect the 
tank to a pickup truck, a long split opened near the right center at the tank bottom. 
Approximately 1,300 gallons of poisonous and corrosive gas escaped, injuring two 
loaders. Nine days after the accident, one of the injured loaders died. 

The Safety Board said the accident was the result of inadequate welding and insufficient 
radiographic inspection during the tank's manufacture, and lack of periodic testing during 
its service life. The NTSB's report also focused on the cooperative's emergency 
preparedness and concluded that its procedures were ineffective because they did not 
direct the nurse tank loaders to evacuate the area when an anhydrous ammonia release 
posed an inhalation hazard. The Board determined that the cooperative should have 
directed its loaders, when faced with a significant release, to evacuate the release area 
before taking steps to flush affected skin and tissue with water. 

When the nurse tank split open at the Calamus facility, it quickly lost the bulk of its 
liquid contents, investigators said. The spilled anhydrous ammonia rapidly vaporized, and 
for some minutes the vapor cloud probably enveloped the platform, the immersion tub, 
and the two loaders. When an anhydrous ammonia release occurs, it puts those in the 
vicinity at risk of two types of exposure?inhalation and skin/soft tissue exposure.

Hazardous materials authorities have indicated that evacuation is the appropriate response 
to minimize inhalation exposure from significant anhydrous ammonia releases, the Safety 
Board said. The material for anhydrous ammonia provided by River Valley's anhydrous 
ammonia supplier states that when an inhalation exposure to anhydrous ammonia occurs, 
the victim should immediately be moved away from the exposure site and into fresh air. 
According to the National Institute for Occupational Safety and Health (NIOSH), in its 
study HAZOP of Anhydrous Ammonia Use in Agriculture, workers should "immediately 
vacate the area by heading upwind" when an anhydrous ammonia release occurs. The 
2000 Emergency Response Guidebook recommends that when a large spill of anhydrous 
ammonia takes place, people should move at least 200 feet away from the source. 

By contrast, River Valley told its loading employees that in the event of an anhydrous 
ammonia release to immerse themselves in the nearest water-filled tub, which was in the 
immediate proximity of the release from the nurse tank, leaving the loaders at risk of 
inhalation exposure. 

The loaders evidently tried to immerse themselves in the nearest water-filled immersion 
tub, which was on the loading platform. Immersion tubs enable workers to wash 
corrosive liquid from their skin and soft tissues. They are not designed to provide 
protection from or treatment for inhalation of chemical vapor. 

Although the loader immersed in the tub received some protection from skin and tissue 
exposure, neither loader was able to avoid inhaling the ammonia vapor. The loader who 
was not initially immersed in the tub, and who subsequently died from his injuries, 
remained at risk not only to the inhalation hazards but also to the damaging effect of the 
gas on his skin, investigators concluded. 

According to The Fertilizer Institute, the estimated 200,000 nurse tanks in service apply 
between 1 million and 1.5 million loads of anhydrous ammonia to fields annually. 

For the complete accident report, visit the NTSB Web site at this address: 
http://www.ntsb.gov/publictn/2004/HZM0401.pdf