Anhydrous Ammonia: Managing The Risks (continued)

AE-1149 (Revised), August 2008

Nurse Tank Safety Check (continued)

Nurse Tank Gauges and Valves

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. A suggested checklist is provided in Table 5, Nurse Tank Valve and Gauge Safety Checklist. When a component is found to be defective, it must be repaired or replaced.

Table 5. Nurse Tank Valve and Gauge Safety Checklist*

* If any items are marked "Not OK," they should be replaced.

The liquid withdrawal valve (Figure 4) 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 The intake for this valve reaches nearly to the bottom of the tank so that liquid ammonia will be withdrawn until the tank is nearly empty.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 (Figure 5). The excess flow valve has a five-year replacement requirement.

Figure 5. Excess Flow Valve (3KB b&w illustration)

The liquid fill valve (Figure 4) 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 (Figure 4) 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 percent full of liquid (Figure 6). The valve should be partially opened when the tank is being filled so it will bleed off, or spurt, liquid anhydrous ammonia when the tank is 85 percent full. The gauge is accurate only if the tank is level. Do not continue filling the tank after the valve releases liquid anhydrous ammonia.

Figure 6. Fixed Liquid Level Gauge (4KB b&w illustration)

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 (Figure 7). It opens at 365 psi to relieve excess pressure due to liquid expansion.

Figure 7. Hydrostatic Relief Valve (2KB b&w illustration)

The liquid level float gauge indicates the level of liquid anhydrous ammonia in the tank (Figure 8). The fixed liquid level gauge (Figure 4) should be used to determine the 85 percent full level when filling the tank instead of the liquid level float gauge.

Figure 8. Float Gauge (3KB b&w illustration)

The safety relief valve also is known as the pressure-relief valve. This valve is on top of the tank (Figure 4) and prevents excessive pressure from building up in the tank caused by overfilling or expansion from heat (Figure 9). 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.

Figure 9. Pressure-Relief Valve (4KB b&w illustration)

The rotary gauge (Figure 10) 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. 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.

Figure 10. Rotary Gauge (3KB b&w illustration)

Back-check valves (Figure 11), 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. A flow in the wrong direction causes the valve to snap shut. It will open only when the direction of flow is correct.

Figure 11. Back-Check Valve (3KB b&w illustration)

The emergency shut-off valve is another valve not found on a nurse or applicator tank (Figure 12). 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.

Figure 12. Emergency Shut Off Valve (6KB b&w illustration)

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.

Nurse Tank Running Gear

The nurse tank running gear should be inspected before each use. Refer to Table 6 for a suggested safety checklist.

Table 6. Nurse Tank Running Gear Components

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.

Anhydrous Ammonia Applicator Components

The breakaway coupler (Figure 13) is designed to prevent an uncontrolled release when a nurse tank releases from the applicator and the nurse tank hose separates. A spring-loaded valve closes when the coupler separates from the main body to prevent anhydrous ammonia from flowing out of the hose or the applicator. The breakaway coupler is dated and has a service life of three years. The replacement date is stamped on the coupler.

Figure 13. Breakaway Coupler (5KB b&w illustration)

Follow these steps to reconnect a breakaway coupler:

1. Put on the gloves and goggles from the emergency kit on the nurse tank. Make sure emergency water is available.
2. Check the wind direction. Always stand upwind when handling ammonia equipment so that ammonia vapors blow away from you.
3. Pick up the hose from the ground and place it on the tank or applicator so it is not in the way when reattaching the nurse tank and the applicator.
4. Make necessary hitch repairs or replacements and reattach the nurse tank to the applicator, using a safety clip on the hitch pin and the nurse tank safety chains.
5. Close the nurse tank liquid withdrawal valve, nurse tank hose valve and the applicator flow meter. Failure to close any of these valves may result in a dangerous spray of ammonia.
6. Point the hose end away from you and close the hose end valve. Point the bleed hole away from your face and slowly open the bleeder valve.
7. Stand so that your face is away from the opening of the bleeder valve on the breakaway coupler. Slowly open the bleeder valve on the breakaway coupler unit. Keep the bleeder valves open until all reconnections have been made. Liquid ammonia in the hose can vaporize and pressurize the hose after the hose valves are closed.
8. Open the applicator flow meter shut-off valve to prevent pressure from building in the applicator flow meter system.
9. AFTER the ammonia has been drained from the hose and breakaway coupler body, clean all soil and debris from the hose end and breakaway coupler fitting. Soil or debris can interfere with the applicator flow metering system.
10. Insert the male coupler (hose end fitting) back into the female coupler of the breakaway coupler unit. Be sure the couplers are securely reattached.
11. Close the applicator flow meter and all bleeder valves that were opened.
12. Open the nurse tank liquid withdrawal valve and hose end valve when ready. If all connections are tight and do not leak, replace the gloves and goggles in the nurse tank emergency kit.

Follow the instructions for your particular breakaway valve if they differ from the instructions listed above. However, never modify the written instructions by changing or eliminating steps.

Safety features should be checked each time before using the equipment in the field. See Table 7 for a checklist to prevent forgetting a safety check.

Table 7. Applicator Components

Always use a hitch pin with a safety clip to be sure the nurse tank will not detach from the applicator and the applicator will not detach from the tractor. Use the safety chains when moving equipment on public roads.

The condition of the applicator knives is important for safety reasons as well as quality application. Knives in poor condition may result in frequent stops for cleaning and unplugging, increasing exposure to anhydrous ammonia. Plugged knives can trap pressurized ammonia that will be released when the knife is cleared.

Sagging low-pressure discharge hoses are a source of exposure to anhydrous ammonia because the anhydrous ammonia in the sag will flow toward the applicator knife and be released when the machine is lifted out of the ground. All low-pressure tubes on the applicator should be of the same length for a uniform delivery to the knives. Extra hose lengths can be coiled and securely fastened to the frame to reduce sagging.

When unplugging metering screens, close the liquid withdrawal valve on the nurse tank and the hose valve on the applicator, open the bleeder valve on the applicator side of the nurse tank withdrawal valve and turn the applicator to bleed the distribution system. Leave the system open until the screen is cleaned and replaced.

Transport Safety Practices

Highway towing rules:

• Tow no more than two portable tanks behind one vehicle.
• The speed limit is 25 miles per hour.
• The overall length of the entire transporting unit may not exceed 75 feet.
• Nurse tanks can be transported only on public roads between sunrise and sunset.
• A slow moving vehicle (SMV) emblem or a lighted rotating or flashing amber light must be displayed on the rear of the towed nurse tank.
• Safety chains must be used if nurse tanks are towed faster than 15 miles per hour.
• Tanks must be identified in the front and rear and both sides with the words "ANHYDROUS AMMONIA" in letters not less than 2 inches high.
• Tanks must be placarded in the front and rear and on both sides with approved Department of Transportation (DOT) "NON-FLAMMABLE GAS" placards.
• The DOT "NON-FLAMMABLE GAS" placard ("1005" decals) are also required to be on the nurse tank.

Should a mishap occur while transporting anhydrous ammonia, the spill or leak should be approached from upwind whenever possible. To minimize the gas cloud, water should be sprayed on the point of discharge, not just on the tank. If emergency help is needed, call toll-free 1-800-472-2121 or 911.

Safe Field Practices

• Always have an 8-ounce squirt bottle of water available when working with any anhydrous ammonia equipment.
• Wear gloves and goggles when connecting or disconnecting nurse tanks and applicators.
• Always have a backup set of gloves, goggles, respirator with approved cartridge and 5 gallons of fresh water when applying or transporting anhydrous ammonia nurse tanks.
• Always work upwind of anhydrous ammonia equipment.
• Carry the nurse tank hose by the valve body or coupling rather than by the valve wheel or control handle.
• Clean hose/applicator connectors before connecting them.
• Hand tighten the valve wheel; overtightening can damage the valve or seals.
• Follow the recommended procedure for connecting and disconnecting nurse tanks and applicators.

Private Stationary Storage Facilities

Stationary storage facilities not used for retail sales or disbursement of anhydrous ammonia are required to have the same safety facilities as commercial stationary storage facilities. The requirements are based on the storage capacity of the facility, regardless of whether retail sales are being conducted or not.

Required Safety Equipment

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

Personal Protective Equipment

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.

Farm Transfer Facilities

Agricultural producers can transfer anhydrous ammonia only from cargo tanks to nurse tanks when the following safety requirements are met:

1. The transport tank must have complete, up-to-date certification and labeling.
2. Wheel chocks of adequate size must be used on the transport tank and the nurse tank before the transfer processes begin.
3. The following articles must be on the transport tank: 1) a 5-gallon reservoir of clean water, 2) ammonia-impervious gloves, 3) two full-face piece respirators with ammonia canisters and nonvented goggles.
4. The following articles must be on nurse tanks: 1) a 5-gallon reservoir of clean water, 2) a legal decal illustrating the step-by-step ammonia transfer process and 3) a legal decal explaining first aid procedures to follow when exposed to anhydrous ammonia.
5. The transfer process must be done on a firm, well-prepared, level surface during daylight hours on the owner's or consignee's property;

The following minimum setback distances apply to transfer facilities:

1. 50 feet from any adjoining property or any highway or railroad mainline
2. 450 feet from any residence or public assembly
3. 750 feet from any institutional residence
4. one mile from any city limits

Transport tank truck owners must provide written notice to the board of county commissioners of the intention to transfer anhydrous ammonia from any transport tank to nurse tanks in the particular county.

Rules for Anhydrous Ammonia Nurse Tank and Storage Container Locks

The North Dakota Legislature adopted the following rules as a pilot project for locking anhydrous ammonia tanks in several North Dakota counties. The pilot project is coordinated by the North Dakota Insurance Commission, Anhydrous Ammonia Inspection Office, State Capitol, Fifth Floor, 600 East Boulevard Ave., Bismarck, ND 58505-0320. These rules are included in this publication as recommended practices for anyone working with anhydrous ammonia in agriculture. More information can be obtained by contacting the Anhydrous Ammonia Inspection Office by telephone at (701) 328-0440 or e-mail at insurance@nd.gov.

1. An owner or operator of an anhydrous ammonia storage facility may not fill a nurse tank or applicator tank unless the tank is equipped with an approved locking device.
2. Unless an anhydrous ammonia nurse tank or applicator tank is empty, an owner or operator of an anhydrous ammonia storage facility may not store an unattended nurse tank or applicator tank at a facility unless the tank has an approved locking device installed.
3. Unless an anhydrous ammonia nurse tank or applicator tank is empty, a person in possession of the tank outside of an anhydrous ammonia storage facility must install an approved locking device on the tank if the tank is left unattended overnight.
4. Unless a locking device is integral to the liquid withdrawal valve, a person transporting a nurse tank or applicator tank must remove the locking device during transit.
5. An anhydrous ammonia storage facility owner or operator must be present at the pickup of a nurse tank or applicator tank at an anhydrous ammonia storage facility unless the tank is empty or unless an approved locking device is installed on the tank.
6. A person in possession of a nurse tank or an applicator tank may not drop off the tank at an anhydrous ammonia storage facility if the owner or operator is not present unless the tank is empty or unless an approved locking device is installed on the tank.
7. Anhydrous ammonia may not be transferred from an anhydrous ammonia bulk delivery vehicle to a nurse tank or applicator tank unless the tank is equipped with an approved locking device.
8. A storage container must have approved locking devices installed on the main container stop valves whenever the storage facility is unattended unless the container is empty.

Summary

Anhydrous ammonia is a fertilizer commonly used in North Dakota agriculture. The risk of working with it is high because of its strong affinity for water, caustic nature, high pressure and very low temperature created when pressure is released. The caustic nature of anhydrous ammonia causes severe chemical burning injury. The extremely low temperature causes frostbite and frozen tissue.

Flushing with water is the best and only first aid treatment for an exposure. Exposure to the eyes and respiratory system presents the greatest challenge in administering first aid. The victim always should be taken to professional medical help as soon as possible. Continue to flush the exposure while in transport.

Many safety features must be built into the anhydrous ammonia handling and application system. Some safety features have service life limitations supported by state laws because these features are not repairable in the field and require trained technicians to service them. The purpose for these service life limitations is to keep these parts in good working condition and to minimize the risk of failure.

Storing anhydrous ammonia in large bulk containers on the farm presents hazards similar to storage at commercial installations. The need for particular safety equipment and procedures is the same, regardless of the location of the facility. All bulk storage facilities have specific required safety equipment and procedures.

References

Aherin, R., L. Schultz, 1984. Using Anhydrous Ammonia Safely on the Farm, Educational Package AG-EP-2192, Agricultural Extension Service, University of Minnesota.

American National Standards Institute Inc., 1981. Safety Requirements for the Storage and Handling of Anhydrous Ammonia, Publication K61.

Anhydrous Ammonia Safety, 1990. Iowa Fertilizer and Chemical Association.

Doss, H.J., 1998. Preventing Ammonia Burns and How to Treat Them, Michigan State University Extension, Michigan State University.

North Dakota Century Code, Article 7-12, Chapters 7-12-01 through 7-12-01-08, Anhydrous Ammonia Regulation.

North Dakota Century Code, Chapter 19-20.2, Sections 19-20.2-01 through 19-20.2-10, Anhydrous Ammonia Facilities.

The Fertilizer Institute, 1982. External Visual Inspection Guidelines for Anhydrous Ammonia Nurse Tanks and Applicator Tanks.

Grisso, R.D., D. Morgan and R.D. Schnieder, 1994. Using Agricultural Anhydrous Ammonia Safely, EC94-738-B, University of Nebraska Cooperative Extension, University of Nebraska.

Schutske, J.M., 1998. Using Anhydrous Ammonia Safely on the Farm, Minnesota Extension Service, University of Minnesota.

Schwab, C.V., M. Hanna and L. Miller, 2002. Play it Safe with Anhydrous Ammonia, University Extension, Iowa State University.

NDCC 28-32-02 Chapter 19-20.2 Anhydrous Ammonia Facilities. Effective April 1, 2004.

[ BACK ]

[ Introduction ] [ Types of Exposure ]
[ Protective Equipment for Anhydrous Ammonia ] [ Nurse Tank Safety Check ]
[ Anhydrous Ammonia Applicator Components ] [ Transport Safety Practices ]
[ Safe Field Practices ] [ Private Stationary Storage Facilities ] [ Farm Transfer Facilities ]
[ Rules for Anhydrous Ammonia Nurse Tank and Storage Container Locks ] [ Summary ] [ References ]

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AE-1149 (Revised), August 2008