Safely Storing and Handling Anhydrous Ammonia

Industrial anhydrous ammonia is an affordable fertilizer, making its use widespread throughout the agricultural community. It also has a vast array of other uses in countless other industries, and more than 110 million tons of the substance are used each year around the globe. 

But handled incorrectly and anhydrous ammonia can have a dangerous — and sometimes even deadly — impact. Storage tanks can rupture or explode and have all kinds of severe consequences. 

Safely storing and handling anhydrous ammonia is essential. Here’s what you should know. 

Pressure and Temperature of Anhydrous Ammonia in Tanks

One of the most common uses of anhydrous ammonia is as a fertilizer. This is because it is a rich and ready source of nitrogen that’s essential for plant growth. The challenge here is that at atmospheric temperature, anhydrous ammonia is a gas. 

For anhydrous ammonia to stay in liquid form to be injected below the soil for optimum application, it must be compressed and cooled, then stored under pressure to prevent vaporization. 

The pressure in a tank of anhydrous ammonia is so high that one cubic foot of anhydrous ammonia in liquid form produces 855 cubic feet of ammonia gas. 

Storage and nurse tanks for anhydrous ammonia are built to withstand this high pressure and must be able to contain an internal pressure of at least 250 pounds per square inch, but these tanks must be well-maintained and free of defects to ensure safety. Tanks should be inspected daily to ensure there are no potential weaknesses or issues. 

Each time a nurse tank is filled, users should check the liquid level gauge and the pressure gauge to be sure they are working properly and are consistent in their readings. Nurse tanks with faulty gauges should never be used, and to repair or replace a faulty part, the entire tank must be emptied, and the tank pressure must reach zero before work can begin.

Terminal storage tanks for anhydrous ammonia should be stored at -28° Fahrenheit to keep tank pressure to a minimum. At this temperature, the storage pressure is less than 1 pound per square inch, much less pressure than that of anhydrous ammonia stored at atmospheric temperature.

A Note About Pressurized and Cooled Anhydrous Ammonia

According to North Dakota State University, when anhydrous ammonia is released from compression into the atmosphere, the temperature drops from 100° Fahrenheit to -28° Fahrenheit. At this temperature, ammonia can freeze-burn human skin on contact — and clothing can actually freeze directly to the skin. 

Because anhydrous ammonia is stored under high pressure, a sudden rupture in a tank or mechanism can shoot ammonia 10 to 20 feet from the point of release. This means that much care should be taken to inspect tanks and mechanisms for any defects, as a rupture can be very dangerous. 

Maintaining Equipment

Regardless of whether you own or lease equipment for anhydrous ammonia, it must be inspected regularly. 

Daily Inspection

Each day, the tank and hoses should be carefully checked, looking for issues like cuts, soft spots, bulges, or kinking with the hoses or slipping at the coupler. Tires should also be inspected for full inflation, looking for cuts, weathering, wear, and for tightness of lug bolts. 

Additionally, the following components should be inspected:

• Tank valves, liquid withdrawal valves, liquid fill valves, and vapor return valves
• Excess flow valves
• Pressure gauges
• Fixed liquid level gauges
• Liquid level float gauges
• Safety relief (SR) valves
• Hydrostatic relief (HR) valves

Several cases call for immediate repair. This includes:

• Leakes in liquid or vapor shut-off valves
• An accident that caused a dent, gouge, crack, or other damage to the tank
• An overturned tank or collision, like with other farm machinery, for example

Annual Inspection

At least once per year, hoses should be laid out straight and examined for cuts that expose reinforcement fabric and other signs of damage that include:

• Soft spots and bulges
• Blistering or a loose outer cover
• Kinking or flattening (as if from a vehicle)
• Slippage of the hose at the coupling

Personal Protective Equipment (PPE) and First Aid

Anhydrous ammonia is incredibly caustic and can severely burn the skin, eyes, and respiratory tract. It’s a strong alkali that can lead to death or injury to body tissue since it is so caustic and corrosive. Those characteristics, combined with its freezing, dehydrating properties, plus its strong affinity for water and quick evaporation, can create an instant freeze-drying effect when it comes in contact with body tissue.

Anhydrous ammonia makes it very difficult to breathe and can cause pulmonary toxicity and other serious damage to the lungs. It’s likely that if you are exposed to ammonia, even at low concentrations, it will drive you away from the scene. When anhydrous ammonia is inhaled, it can burn the respiratory system very quickly. 

For these reasons, when dealing with anhydrous ammonia, certain personal protective equipment must be worn. This includes:

• Goggles
• Rubber gloves
• Chemical-resistant protective clothing

In addition to goggles, The Ohio State University Extension recommends wearing a face shield or other full-face respirator to protect the eyes and face from a direct blast of anhydrous ammonia. Those working around anhydrous ammonia should never wear contact lenses, as they can trap the gas between the contact lens and the eye and freeze contacts to the eye. 

Contact with even small amounts of anhydrous ammonia poses a threat for permanent blindness and disfigurement, which is why protective equipment is so important. 

First Aid

When the skin or eyes come in contact with anhydrous ammonia, they should be flushed with water immediately for at least 15 minutes. Any contaminated clothing needs to be removed quickly but carefully, and if clothing has frozen to the skin, it must be thawed with water before attempting to remove it. 

Affected skin should only be washed with water for the first 24 hours, and those affected should take great care to stay warm and see a physician immediately. It’s essential to have water on hand to flush the eyes and skin in the event of exposure, which means that each vehicle used for anhydrous ammonia must carry a 5-gallon bucket of clean water for flushing the ammonia away, and anyone handling anhydrous ammonia must carry a 6-to-8 ounce squeeze bottle of clean water on their person for fast emergency use. 

Transferring Ammonia

The majority of ammonia accidents happen because of improper transfers or incorrect handling procedures. All owner’s manuals should be carefully followed, and those on-site should never leave during a transfer procedure. 

When filling nurse or applicator tanks, all recommended PPE should be worn, and water should be on hand for flushing ammonia. Nurse tanks should be parked on level ground, downwind from filling, and close to the operation to eliminate stress on hoses. 

Wheels should be blocked to prevent the tank from moving. Because of the threat to tissue and the respiratory system, it’s best to avoid working near any obstacles like fences, buildings, or ditches that can make it hard to evacuate in the event of a rupture or other incident.  

Couplings and connections should all be free of debris before connecting hoses, and workers should carry the filler hose by the valve body or coupling, not the valve wheel, to reduce the chance of the valve wheel opening. 

No tank should ever be overfilled, which means that workers should watch the liquid level of the tank, filling no more than 85% of the total liquid capacity of the tank. Since outside temperatures can fluctuate, it will cause the liquid to expand, so this extra room in the tank is essential to maintain proper pressure. 

If a tank is overfilled and there is no additional vapor space for heating and expanding anhydrous ammonia, the safety relief valve could fail and cause the entire tank to rupture or explode. 

Your Safety Partner

There are so many intricacies in the safe handling and storage of anhydrous ammonia that it’s hard to list them all in one place. You need a partner to help.

At Airgas Specialty Products, we specialize not just in the reliable delivery of anhydrous ammonia but also in the essential services that surround the safe handling of the product. From the engineering of safe systems to field service, plus pump-outs, storage and delivery systems, regular systems maintenance, and other expert guidance, we are here to ensure that your processes are safe to avoid disaster. 

To learn more about how we can keep you in proper operation, connect with us today!