NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

September 24, 1998

Editors: This is the third in a series of six articles on anhydrous ammonia safety.

For Best Protection Know and Use Safety Features of Anhydrous Ammonia Equipment

There are a variety of valves and gauges and safety equipment on anhydrous ammonia nurse tanks. Knowing what the purpose of each is and how to use them are keys to protecting yourself from anhydrous ammonia accidents, says a North Dakota State University agricultural safety specialist.

"The gauges provide vital information on the tank and its contents, and the valves control the ammonia, in either liquid or vapor states," notes George Maher of the NDSU extension Service. "Those gauges and valves may be the tank's most important safety equipment. The emergency supply of water, goggles, gloves and other protective equipment provide back-up protection."

Nurse tanks have the following valves:

• Excess flow valves close automatically if the rate of flow in the nurse tank hose exceeds a safe level, as occurs when a hose is pulled apart because of a hitch pin failure. The valve will not open again until pressure is equal on each side of the valve. The valve should be replaced every five years. An excess flow valve can be found on the liquid fill valve, liquid withdrawal valve, and vapor return valve.
• The liquid fill valve is used when refilling the nurse tank.
• The liquid withdrawal valve is used to release ammonia from the nurse tank to the applicator.
• The vapor return valve is used to return the vapor in the nurse tank to the bulk storage tank when the nurse tank is being refilled.
• The fixed liquid level gauge is not really a gauge but is a bleeder valve. It is open during the refilling process, first releasing a slight amount of vapor and then a very thin stream of liquid ammonia at the 85-percent-full level. The gauge is closed after the tank has been filled.
• The safety relief valve (pop-off valve) on anhydrous ammonia tanks releases excess pressure that can build up when ammonia in an overfilled tank expands because of solar heating. This valve opens when the tank pressure exceeds 250-265 pounds per square inch. It closes when the pressure drops below this amount. Safety relief valves must be replaced every five years.
• A hydrostatic relief valve is on all anhydrous ammonia piping and hoses that have valves on each end. This valve relieves pressure due to liquid expansion and is set to open at 365 pounds per square inch.
• All hoses and valves have bleeder valves. Bleeder valves "bleed", or drain, pressurized anhydrous ammonia from a closed hose or valve. Opening a bleeder valve releases pressurized anhydrous ammonia slowly to minimize the risk of a sudden release and exposure. Always position yourself upwind or crosswind from a bleeder valve to be opened. Before disconnecting nurse tank hoses, open the bleeder valve to bleed off the ammonia remaining in the hose.

Maher notes that there are two primary gauges on nurse tanks. Float gauges indicate the liquid level of anhydrous ammonia in the nurse tank. Tanks must be level for the float and mechanical system to indicate an accurate liquid level. Even so, the float mechanism is not accurate enough to use at the 85-percent-fill level.

The pressure gauge on any ammonia tank indicates the internal pressure of the tank. It does not indicate liquid or vapor quantity, only the pressure, Maher says.

"Breakaway couplers are important safety equipment that should be used every time a nurse tank is attached to a field applicator," Maher says. "The coupler prevents the uncontrolled release of ammonia if the nurse tank is accidentally uncoupled from the applicator."

The coupler is attached to the applicator and the nurse tank hose is plugged into it. The male part of the breakaway coupler remains attached to the nurse tank hose and can be plugged into the female part attached to the applicator. When the nurse tank is exchanged, the male part of the coupler is disconnected from the nurse tank hose and remains with the applicator.

"If a breakaway coupler is not in use and the nurse tank becomes uncoupled from the applicator, the hose will break due to the strain and release anhydrous ammonia in dangerous, uncontrollable amounts," Maher says.

To safely reconnect a breakaway coupler, a specific procedure of closing valves and opening bleeder valves must be followed, Maher notes. Always follow the instructions for your particular brand and model of breakaway coupler. The breakaway coupler should be replaced every three years.

Every nurse tank should also include an emergency water reservoir containing five gallons of clean, fresh water. "The water should be changed daily because it can absorb ammonia," Maher says. "Use this water only for first aid to flush any area exposed to anhydrous ammonia. If you use it for general cleaning, you may regret it later if you need it for first aid."

Nurse tanks should also carry a personal protective equipment kit containing gloves and goggles. Gloves should be impervious to anhydrous ammonia and have no holes or rips. The glove cuffs should be long enough that they can be folded back to prevent liquid ammonia from running down the arms. The goggles shall be chemical splash type that do not allow liquid or vapor ro reach the eyes. A face shield may be worn over the goggles but should not replace goggles. Use the goggles and gloves every time connections are made or broken between the nurse tank and the applicator, and whenever plugged applicator knives are worked on, Maher advises.

Tanks should also display legible decals providing instructions for the step-by-step transfer of anhydrous ammonia and first aid procedures to follow when exposed to anhydrous ammonia.

"These valves, gauges and safety equipment make working with anhydrous ammonia relatively safe," Maher says. "But if any of this safety equipment isn't used or maintained properly, the risk becomes very serious and injury or death becomes a very real possibility."

For more information on safety issues relating to anhydrous ammonia applications, refer to "Anhydrous Ammonia: Managing the Risks" (AE-1149), a new publication from the NDSU Extension Service available through your county office. Or contact Maher at (701) 231-8288.

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Source: George Maher (701) 231-8288

Editor: Tom Jirik (701) 231-9629