Planning for and responding to ammonia incidents.The three most common reported causes of ammonia incidents all involve the nurse tank. Incidents happen as the nurse tank is transported to and from a field, during fertilizer application, or when filled. Other causes of incidents that have been reported to the Minnesota Department of Agriculture involve the facility bulk tank and unauthorized tampering of ammonia equipment by those seeking ammonia for illegal drug (methamphetamine) production.  Transportation Accidents
The nurse tank is trucked back and forth from the dealer to the field. Nurse tanks may tip over when its wheels drop into a ditch while the truck driver swerves to avoid traffic or turns too sharply into a driveway. The weakest point(s) of the nurse tank are the valves which are protected by a roll cage. The tank itself is quite sturdy. The vast majority of these nurse tank rollovers do not release any anhydrous ammonia. Most can be uprighted, off-loaded and then returned to the facility for repairs. On occasion the accident is violent enough that the roll cage compresses and the valves are damaged. The pressure relief valve positioned at the rear of the tank can also be damaged during a roll over. During Field Application  A toolbar is hitched up behind a tractor. The tool bar is equipped with knives that inject the ammonia into the soil. The knives can be hydraulically raised and lowered manually from the tractor cab.
Trailing behind the toolbar is the nurse tank. A 350 pound per square inch (psi) rated ammonia hose is attached to the forward valve on the nurse tank and the other end to a “quick coupler” bolted to the toolbar (see schematic). This coupler allows the operator to easily and quickly exchange empty for full nurse tanks. The quick coupler will also pull apart protecting the hoses if the nurse tank separates from the toolbar. After flowing through the coupler the ammonia will then pass through a metering device and then into a manifold that will equally dispense the ammonia liquid to each knife. 
 A common cause of an ammonia release in the field occurs when the quick coupler does not separate if the nurse tank draw bar or draw pin breaks. This causes the withdrawal hose to stretch and tear releasing ammonia liquid. The flow of ammonia through the tear may not be great enough for the nurse tank excess flow valve to spring shut resulting in an uncontrolled release.
A much more dangerous situation occurs when the quick coupler fails to disengage and the withdrawal valve breaks loose from the nurse tank. The excess flow valve will shut stopping any release of liquid ammonia if there is enough flow (which is related to internal tank pressure) up through the dip tube.
Another cause of an ammonia release in the field is too long of a withdrawal hose and not secured properly away from the wheels of the nurse tank. The withdrawal hose can rub against the tires causing it to weaken and eventually rupture. During filling and storage  If a nurse tank is filled to greater than 85% capacity there will be little room left for liquid expansion when the tank warms up. The pressure relief valve will then open releasing vapor and causing the internal tank pressure to drop. After pressure drops to below 250 psi the valve will reseat or close. This valve is operating as it should to protect the tank.
Pressure relief valves may “pop” open releasing ammonia vapor when product is delivered “cold” and then a period of unseasonably warm weather causes the liquid to warm up and expand. Again, this is the normal functioning of the valve. On occasion the pressure relief valve will not reseat and continue to vent ammonia vapor. The nurse tank will need to be safely emptied so that the valve can be replaced. When the toolbars, valves, couplers, hoses, and nurse tanks are routinely inspected and maintained the chances of an ammonia release are quite slim. Other Spill Causes Ammonia Theft. Another cause of a release or threatened release of anhydrous ammonia is the tampering and theft of ammonia by those needing it for the illegal production of methamphetamine (meth). More information on meth can be found by visiting Ammonia Theft and Meth Labs. Weather. Tornadic winds caused the release of ammonia vapor from this bulk tank. The photo shows the damage to the vapor (yellow colored) ammonia piping. The lines that are painted red contain liquid ammonia and were not damaged.  
Buried Lines. Facilities may bury the vapor and liquid lines that connect the bulk tanks to the nurse tank loading islands. On very rare occasions these lines will rust through causing the release of ammonia into the soil. The ammonia odor will clue the manager of the problem and excavation of the contaminated soil will be required. Pull Aways. A “pull away” occurs then a nurse tank is pulled away while the liquid and vapor lines are still attached. There is rarely a release of ammonia in this type of incident with the adoption of break away connections and emergency shut off valves.  
Acknowledgements Schematics are from the University of Nebraska Cooperative Extension publication EC94-737D | 
