Anhydrous Ammonia: Managing The Risks

Ammonia is a chemical compound used as a fertilizer because it is rich in nitrogen. Its chemical formula is NH3, which means that it consists of one atom of nitrogen and three atoms of hydrogen per molecule. Because the atomic weights of nitrogen and hydrogen are not the same, the weight ratio is 82.5% nitrogen to 17.5% hydrogen. Anhydrous means the ammonia is without water. This distinguishes it from ammonia/water solutions.

Odor
Anhydrous ammonia is a clear, colorless gas at standard temperature and pressure conditions and has a very characteristic odor. The odor is the strongest safety feature of the product. At a concentration of only 50 parts per million (ppm), one sniff tells what is in the air. Normally, the odor will drive a person away from the area. A concentration of more than 5,000 ppm will disable a person so that escape is impossible and suffocation results.

Anhydrous ammonia is a liquid when compressed or cooled. It is stored under pressure to prevent vaporization so a large volume can be available for use. One cubic foot of anhydrous ammonia in a liquid state produces 855 cubic feet of ammonia gas. Retail storage tanks and nurse tanks for anhydrous ammonia are built to withstand internal pressures of at least 250 pounds per square inch (psi). Terminal storage tanks refrigerate ammonia to minus 28 degrees Fahrenheit. At this temperature, the storage pressure is less than 1 psi.

When anhydrous ammonia is released from compression in a storage tank (200 psi) to the atmosphere (0 psi), the temperature drops from 100 F to minus 28 F. At this temperature, ammonia freeze-burns human skin on contact. Clothing actually is frozen to the skin. Because anhydrous ammonia is stored under high pressure, a sudden rupture can shoot ammonia 10 to 20 feet from the point of release.

Anhydrous ammonia is generally not considered to be a flammable hazardous product because its temperature of ignition is greater than 1,560 degrees F and the ammonia/air mixture must be 16% to 25% ammonia vapor for ignition.
In spite of the difficulty of igniting such a mixture, never weld on any container or piping that has not been completely decontaminated and cleaned of all ammonia and its salts. Remember, never weld on a closed container of any kind; all containers must be completely cleaned and vented. Apply heat only to open containers, including all piping. Welding should be done only by a welding firm with a type “R” certification in compliance with the North Dakota Century Code.

Anhydrous ammonia contains no water. Anhydrous is the Greek word for “without water.” Anhydrous ammonia has a very strong affinity for water. It requires large quantities of water to neutralize its caustic effects on moist areas of the body. When anhydrous ammonia contacts water, it forms ammonium hydroxide. Living tissue is dehydrated quickly and the cells destroyed on contact. Anhydrous ammonia attacks any moist part of the body: eyes, ears, nose, throat, bronchia, lungs, any moist skin. Any tissue containing moisture is chemically burned.

When anhydrous ammonia comes in contact with water, it forms an alkali that chemically burns animal tissue. The chemical burns into the body tissue unless it is diluted by large quantities of water. Anhydrous ammonia is extremely destructive to animal tissue. Skin is reduced to a sticky, gooey substance as the chemical burn progresses. Skin that is chemically burned by the ammonia actually is killed and is not capable of healing or replacing itself. Damaged tissue must be removed surgically so that healing can proceed. The results often are disfiguring.

Anhydrous ammonia causes freezing and chemical burn wherever skin and clothing are moist. The subzero temperature of  escaping anhydrous ammonia freezes clothing to the body. Do not attempt to remove any clothing that is frozen to the skin. It  must be thawed loose first or skin tissue may be pulled from the victim.

The caustic nature of anhydrous ammonia causes skin and tissue burns similar to burns from heat. Do not apply salves,  creams or ointments of any kind to the injury. The caustic burning can be stopped only by dilution with large quantities of water.

Eyes are continually bathed in moisture. Anhydrous ammonia will seek this moisture. The burns will result in damage to the  eyes, such as cataracts, glaucoma and possibly some permanent vision loss and disfigurement.

If eyes have been exposed to anhydrous ammonia, they must be flushed with water immediately and continually and the victim must be taken to a doctor immediately. Everyone who works with anhydrous ammonia should carry a 6- or 8-ounce squeeze  bottle of fresh water on their person at all times. This small amount of water will last only long enough for the worker to get to a  larger quantity of water, but it may make the difference between blindness and sight. 

Initially, forcing the victim’s eyelids open after the exposure may be necessary. The ammonia trapped under the eyelids must  be flushed out with water or it will continue to burn the eye and related tissues.

At low concentrations, the odor of anhydrous ammonia usually will drive the unprotected worker away from the scene. At a  higher level of concentration (see Table 2), the worker may not escape without inhaling a dangerous dose. The entire  respiratory system is very moist, so anhydrous ammonia will be attracted naturally to that part of the body. When a  concentrated level of anhydrous ammonia is inhaled, it will burn the respiratory system quickly. The victim may hurt too much  to breathe. The respiratory system essentially may be paralyzed due to the pain.

First-response rescue workers may not be able to treat a serious inhalation exposure. Medical technicians may be able to  administer oxygen to aid breathing after their arrival on the scene. Maintaining adequate respiration for the victim until delivery  to a medical facility may be difficult.

Respiratory protection is extremely important, but also limited in what equipment is available. A two-cartridge respirator is  effective only for exposure levels of less than 300 ppm. Canister type respirators may be effective for longer periods at higher  concentrations, but without skin protection, walking through an ammonia cloud is generally not advisable. A self-contained 
breathing apparatus (SCBA), which supplies the air to be breathed, and a sealed, protective hazmat suit are required for  working in a cloud of escaping anhydrous ammonia. Anything less will not sufficiently protect a person in this situation.

Start first aid treatment immediately when someone is exposed to anhydrous ammonia. The chemical burning starts instantly  and the injury becomes worse as time passes. Treatment consists of flushing the affected body area(s) with large quantities of  water.

One short flushing is not sufficient. Maintain a steady flow of water over the affected area(s) until the victim is delivered to  medical help. The water provided with each nurse tank or other container will not be enough. Five gallons flowing in a pencil-sized stream will last approximately seven minutes. Additional water should be carried on every tractor used in field applications and in every field support motor vehicle. Collect as much water as possible and continue flushing while  arrangements are being made to transport the victim to a medical facility. Do not reuse the water; it will not provide relief,  having already absorbed anhydrous ammonia.

Make arrangements to transport the victim to a doctor or hospital immediately after exposure. First aid can be given while transport arrangements are being made, but get the victim to medical care as soon as possible. Notify the hospital that the  victim is being transported. First aid flushing should be continued while in transport.

Clouds of anhydrous ammonia are subject to the unpredictability of air movement; they will change direction as quickly as the breeze. Clouds of ammonia may be nearly invisible in some atmospheric conditions, but they appear as white clouds when the atmosphere is damp. Rain will absorb the ammonia and remove it from the air.

Anhydrous ammonia is heavier than air and will settle in the low areas of the surrounding landscape, such as road ditches, sloughs and valleys. People in threatened areas must be warned of the release and advised to leave the area until the release has been controlled and the area is considered safe for re-entry. These decisions should be made by emergency personnel, such as a local fire department. Animals and livestock should be removed from the threatened area after people have been taken care of first. Most animals will do their best to leave the area long before ammonia concentrations become strong enough to cause them much discomfort.

Additional protective equipment is required for bulk storage of anhydrous ammonia. A rain suit and two canister-type gas masks are required by law in the North Dakota Century Code. They will protect you only in areas of low ammonia concentrations. A  cartridge-type respirator is not approved for use at a bulk storage facility.

Call the local fire department if a major leak occurs. The fire department has self-contained breathing apparatus (SCBA) and  protective suits. SCBA units supply air to breath, rather than just filtering available air. The protective suits are sealed to keep  anhydrous ammonia out.

A water reservoir of at least 150 gallons of clean water must be available at a bulk facility, which would enable a person to  submerge in water should they be exposed to anhydrous ammonia. A minimum 150-gallon stock water tank will meet this  requirement.

Keep the informative decals on the equipment up to date. The decals indicate what each system component does and  identifies the first aid water, other protective equipment and protective procedures. 

Keep the operator’s manual for the bulk storage unit in a readily available place for reference when handling the ammonia. Review the instructions when needed.

The bleeder valve is used to bleed or drain pressurized anhydrous ammonia from a closed hose or valve.

Bleeder Valve

Opening a bleeder valve will release pressurized anhydrous ammonia slowly to minimize the risk of a sudden release and  exposure. Bleeder valves should be opened slowly. Always position yourself upwind or across wind from a bleeder valve to be  opened. Never disconnect a nurse tank hose without first draining it with the bleeder valve. Bleeder valves are used in several  processes of handling anhydrous ammonia.

The nurse tank hose should be inspected daily. It must be maintained in a safe condition because it transfers anhydrous ammonia under high pressure from the nurse tank to the applicator tool bar. Although the hose is protected by an excess flow valve in the liquid withdrawal valve on the nurse tank, the hose must be in good condition to prevent an uncontrolled release.

NURSE TANK HOSE SAFETY CHECKLIST

Check the nurse tank hose all of the following items.

• Cuts or abrasions
• Soft spots/bulges
• Blistering/loose layers
• Kinking/flattening
• Coupler/hose slippage
• Type of fittings (incorrect metals)
• Outdated hose

If any of these checklist items are present the nurse tank hose should be replaced.

The nurse tank hose must be made of approved materials and braiding, such as rayon, rylon/Kevlar or stainless steel. A hose made with rayon braiding is good for two years from the date of manufacture while a hose with nylon/Kevlar is good for four years from the date of manufacture and stainless steel is good for six years from the date of manufacture.

Nurse Tank Hose. The nurse tank hose should have a label that incudes the following elements: Hose Type (e.g. "NYLON"), Working Pressure (e.g. "350 PSI MAX WP"), Manufacturing Date ("1991"), and Manufacturer I.D. (e.g. "TFI-167-DE2").

The nurse tank hose always should be “parked” or attached to the Acme “parking” fitting on the nurse tank when not in use during the season. Do not drape a hose over any edge that allows the hose to become flat. During the off-season, the hose should be stored in a vertical position, hanging from the shoulder of a coupling in a cool, dry location.

Most hose failures occur within 12 inches of the hose end due to flexing of the hose while attached to the nurse tank or applicator. Select hose fittings that will provide the most support and minimize this type of flexing. Examine the hose carefully before making connections to find problems that may cause a hose failure.

The tank must conform to design guidelines provided by the American National Standards Institute (ANSI). The tank and all of its fittings, including pressure welds, fittings, gauges, hoses, safety valves and metering devices, must withstand a minimum working pressure of 250 psi.

Applicator tank and valves. The pressure gauge is at the top of the tank at one end. The safety relief valve is next to it, followed by the liquid withdrawal valve, vapor valve, fixed liquid level gauge, and the liquid fill valve. The liquid level float gauge is on the side of the tank.

Nurse tank and valves. The liquid withdrawal valve with attached hose is on top of the tank at one end. Next to i is the liquid fill valve, followed by the pressure gauge, fixed liquid level valve, vapor valve, and liquid level float gauge. The safety relief valve is at the other end at the top of the tank and the drain is at the bottom of the tank.

The tank should be painted silver or white to reduce temperatures and pressures resulting from solar heating. Surface defects, such as rust, dents and gouges, reduce the integrity of the tank as a high-pressure container and are not acceptable. North Dakota Century Code specifies that less than 10% of the surface may be corroded or missing paint.

The nurse tank hose should have an Acme “parking fitting” to be “parked” on when not in use. The fitting should be installed  in such a position that prevents strain on the hose when it is “parked.” 

The tank must be labeled correctly on each end and side with the green diamond around the words DOT (Department of  Transportation) “NONFLAMMABLE GAS” and on each side and end with “Anhydrous Ammonia” in letters not less than 2  inches high. Safety and first aid instructions must be on the tank. All valves must be identified as to liquid or vapor service.

North Dakota law requires anhydrous ammonia nurse tanks, empty or full, to display either a slow moving vehicle (SMV) sign or a lighted rotating or flashing amber light while on a public roadway. Any vehicle or towed trailer/wagon displaying an  SMV sign is restricted to a road speed of not more than 25 miles per hour. Anhydrous ammonia nurse tanks, therefore, cannot be towed at a speed exceeding 25 miles per hour.

The protective equipment kit, containing gloves and goggles, must be attached to the tank and accessible from the ground.  The emergency water reservoir also must be attached to the nurse tank and be filled with 5 gallons of clean, fresh water.  The water should be changed at least daily because it can absorb ammonia from the immediate environment.

NURSE TANK SAFETY CHECKLIST

Check the nurse tank to determine if all of the following items are OK.

• Paint
• Rust
• Dents
• Gouges
• Parking fitting for hose
• DOT decals
• Anhydrous ammonia decals
• Safety decals
• First aid decals
• Valve labeling decals
• Slow moving sign
• Safety kit (gloves, goggles)
• First aid water

Regularly scheduled maintenance must be conducted to ensure that the gauges and valves on a nurse tank are suitable for service. The degree of hazard increases as parts get older. A visual inspection should be completed before each use.

Some nurse tank components have a service life limitation based on time. The service life cannot be extended. Use a checklist to keep an accurate inventory when parts need to be replaced. When a component is found to be defective, it must be repaired or replaced.

NURSE TANK VALVE AND GAUGE SAFETY CHECKLIST

Check the following nurse tank parts to determine if they are OK.

• Liquid withdrawal valve (5-year replacement)
• Excess flow valve (5-year replacement)
• Liquid fill valve (5-year replacement)
• Pressure gauge
• Vapor return valve (5-year replacement)
• Liquid level float gauge
• Hydrostatic relief valve
• Bleeder valves
• Pressure/safety relief valve (5-year replacement)
• Roll cage for valves/gauges
• Tank drain

If any these checklist items are not OK, they should be replaced.

The liquid withdrawal valve connects the nurse tank hose to the interior of the nurse tank for removal of the ammonia. The intake for this valve reaches nearly to the bottom of the tank so that liquid ammonia will be withdrawn until the tank is nearly empty. It contains an excess flow valve preventing anhydrous ammonia from flowing out of the tank too quickly if the nurse tank hose breaks. The excess flow valve has a five-year replacement requirement.

Excess Flow Valve

 The liquid fill valve is used while filling the nurse tank from a bulk storage facility. It has an excess flow valve preventing anhydrous ammonia from flowing back out of the nurse tank if the hose breaks. This valve has a five-year replacement requirement.

The pressure gauge indicates the interior pressure of the nurse tank. This interior pressure is affected by the quantity and temperature of the anhydrous ammonia in the tank. The pressure gauge does not have a time limit to its service life, so it needs to be replaced only when it fails to function properly.

The fixed liquid level gauge is a bleeder valve with a tube extending into the tank to a depth where the tank would be 85%  full of liquid.

Fixed Liquid Level Gauge

The valve should be opened partially when the tank is being filled so it will bleed off, or spurt, liquid anhydrous ammonia  when the tank is 85% full. The gauge is accurate only if the tank is level. Do not continue filling the tank after the valve  releases liquid anhydrous ammonia.

The vapor return valve is used while filling the nurse tank at a bulk storage facility. As liquid anhydrous ammonia is  transferred into the nurse tank, the vapor in the nurse tank is transferred to the bulk storage tank. The vapor valve has an  excess flow valve (which has a five-year replacement requirement). The excess flow valve prevents release of anhydrous ammonia vapors from the nurse tank if the vapor valve fails.

A hydrostatic relief valve should be used anywhere anhydrous ammonia may be trapped in any section of the liquid or vapor  lines of the system.

Hydrostatic Relief Valve

 It opens at 365 psi to relieve excess pressure due to liquid expansion.

The liquid level float gauge indicates the level of liquid anhydrous ammonia in the tank.

Float Gauge

The fixed liquid level gauge should be used to determine the 85% full level when filling the tank instead of the liquid level  float gauge.

The safety relief valve also is known as the pressure-relief valve. This valve is on top of the tank and prevents excessive  pressure from building up in the tank caused by overfilling or expansion from heat.

Pressure-relief Valve

The valve opens directly to the atmosphere when the tank reaches 250 to 265 psi and closes when the interior pressure  drops below 250 psi. It must be replaced every five years if it has nonmetallic seats and tested every five years in lieu of  replacement if it has metallic seats. Repairs can be done only by a repair organization with a valid “VR” certificate of  authorization from the National Board of Boiler and Pressure Vessel Inspectors. This valve must have a rain cap in place to  prevent damage from moisture and corrosion. The safety relief valve is not adjustable and should be replaced if it is  inoperable.

The rotary gauge mounted on the end of an anhydrous ammonia tank, bulk tank, nurse tank or applicator tank  consists of a dip tube inside the tank and a bleeder valve.

Rotary Gauge. The gauge includes a tube with a pointer at one end. The tube turns with the pointer. Next to the pointer is the dial indicator which shows the percentage of anhydrous ammonia in the tank.

This gauge is used to determine the actual level of anhydrous ammonia in the tank. It is accurate only if the tank is level.  The indicator shows the liquid level in the tank when the bleeder valve is opened and the knob is rotated to the point where liquid spurts from the bleeder valve.

Back-check valves, part of the bulk storage facility, are used to control the direction of flow of anhydrous ammonia when unloading a truck or rail tank car, preventing a backflow from the bulk tank to the truck or rail tank car.

Back-check Valve

 A flow in the wrong direction causes the valve to snap shut. It will open only when the direction of flow is correct.

The emergency shut-off valve is another valve not found on a nurse or applicator tank.

Emergency Shut-off Valve. The valve has a cable attachment for remote release, an operating lever, and a poppet.

 It also is part of the bulk storage facility used to stop the flow of anhydrous ammonia when the operator of the facility detects an emergency situation and decides to stop the transfer of anhydrous ammonia immediately. This valve is on the discharge side of the transfer pump.

The roll cage protects gauges and valves if the nurse tank rolls over. The roll cage must be strong enough to prevent damage to the gauges and valves.

The nurse tank running gear should be inspected before each use.

NURSE TANK RUNNING GEAR SAFETY CHECKLIST

Check the nurse tank running gear to determine if all of the following items are OK.

• Hitch pin and safety clip
• Safety chains and hooks
• Lug nuts tight on wheels
• Tire pressure
• Good tires
• Solid frame, no cracks
• Free-rolling wheels
• Proper steering
• Tank secure

The use of a safety clip on the hitch pin when towing anhydrous ammonia nurse tanks on and off the road is essential to your safety and that of the public. The safety clip will keep the hitch pin from working out and releasing the nurse tank.

Always attach safety chains when towing anhydrous ammonia nurse tanks on public roads. Safety chains are required by North Dakota law. The safety clip will keep the hitch pin from working out and releasing the nurse tank. The chains help ensure that the vehicle towing the nurse tank will remain in control of the nurse tank if the hitch pin fails.

Check the air pressure in the tires each time the nurse tank is used and inspect them for cuts, bruises and tread wear. Tires used on nurse tanks are designed for low-speed travel not to exceed 25 mph. Follow the restricted speed requirements for anhydrous ammonia both on and off the road.

Inspect the nurse tank wagon frame before each use. inspecting for cracks, broken welds and bent members. The bolts and nuts that attach the tank to the frame are especially subject to loosening or breaking.

Wheel bearings should be checked and repacked annually. Steering systems should be checked regularly and lubricated

The following items are required at anhydrous ammonia bulk storage facilities:

1. A loading platform because climbing or standing on the wheels of nurse tanks is not permitted while filling nurse tanks
2. A safety shower or an open water reservoir capable of holding at least 150 gallons of water for complete body immersion
3. A fire extinguisher
4. A telephone or a two-way FM radio

The following five personal protective equipment items are required by the North Dakota Anhydrous Ammonia Law to be readily available at the storage site:

1. Two full-face gas masks with spare ammonia
2. One pair of ammonia-impervious, protective gloves
3. One pair of nonvented goggles that meet ANSI Z87.1 impact specifications
4. One pair of impervious protective boots
5. One “slicker suit,” a rain suit that is impervious to ammonia

Operators of anhydrous ammonia storage facilities must be trained in safe operating procedures and the training documented by signed forms showing the type of training, the date of training, the persons trained and the person doing the training. These forms must be on record for at least three years and available for review at the facility during normal business hours.