Anhydrous Ammonia: Managing The Risks

AE-1149, August 1998
George G. Maher, Ag Safety Specialist

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
Summary
References

Introduction

More anhydrous ammonia is used as fertilizer in North Dakota than any other nitrogen fertilizer source. Anhydrous ammonia is classified as a hazardous substance. Most accidents with anhydrous ammonia are due to uncontrolled releases. Few problems occur when the ammonia is being handled and applied as intended. Most uncontrolled releases are due to improper procedures, careless or untrained workers, or faulty equipment. Protective equipment is required by law to be available where anhydrous ammonia is handled or applied. Wearing protective equipment greatly reduces the chance of injury from an ammonia release. Countless tons of anhydrous ammonia are applied every crop year without problems; safe procedures and quality equipment do work.

Anhydrous ammonia has the potential to be one of the most dangerous chemicals used in agriculture today. It is used and stored under high pressures, which requires specially designed and well-maintained equipment. Those who work with anhydrous ammonia must be trained to follow exact procedures in handling it.

Chemistry of Anhydrous Ammonia

Ammonia is a chemical compound used as a fertilizer because it is rich in nitrogen. Its 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 percent nitrogen and 17.5 percent hydrogen. Anhydrous means the ammonia is without water. This distinguishes it from ammonia/water solutions.

Characteristics of Anhydrous Ammonia

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 only 50 parts per million concentration, one sniff tells what is in the air. Normally, the odor will drive a person away from the area. A concentration of more than 5000 parts per million will disable a person so that escape is impossible and suffocation results.

Pressure for Storage

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 F. At this temperature, the storage pressure is less than 1 psi.

Temperature/Pressure Relationships

When anhydrous ammonia is released from compression in a storage tank (200 psi) to the atmosphere (0 psi), the temperature drops from 100 degrees F to minus 28 degrees F. At this temperature, ammonia will freeze-burn the skin on contact. Clothing is actually frozen to the skin. Another risk is that ammonia when released will quickly expand from the point of release. A suddent rupture can shoot ammonia 10 to 20 feet from the point of release.

Table 1. Temperature and Pressure Relationships

  Degrees F   Pressure (psi)
------------------------------
    -28 F         0 psi
      0 F        16 psi
     32 F        48 psi
     60 F        93 psi
    100 F       200 psi

Flammability

Anhydrous ammonia is generally not considered to be a flammable hazardous product. Its temperature of ignition is higher than 1560 degrees F, making it rather difficult to ignite. The ammonia/air mixture must be 16 to 25 percent ammonia vapor.

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. Then, the welding can be done by a welding firm with a type "R" certification in compliance with the North Dakota Century Code.

Anhydrous

Anhydrous ammonia contains no water. Anhydrous is the Greek word for 'without water.' When anhydrous ammonia contacts water it forms ammonium hydroxide. Living tissue is quickly dehydrated and the cells destroyed. It attacks any part of the body that is moist—eyes, ears, nose, throat, bronchia, lungs, any moist skin. Any tissue that contains moisture is chemically burned.

Caustic Nature

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

Types of Exposure

Anhydrous ammonia has a very strong affinity for water. It requires vast quantities of water to neutralize the caustic effects of anhydrous ammonia on moist areas of the body. Such areas include the eyes, breathing system (mouth, throat, bronchial tubes, lungs), and especially moist skin (skin which is damp from perspiration; arm pits, groin, forehead, scalp, feet).

Skin

Anhydrous ammonia will cause freezing and chemical burn wherever the skin and clothing are moist. The sub-zero temperature of escaping anhydrous ammonia will freeze 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 will cause 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 only be stopped by dilution with large quantities of water.

Eyes

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

If the eyes have been exposed to anhydrous ammonia they must be immediately and continually flushed with water and then victim 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, it may be necessary to force the victim's eyelids open after the exposure. The ammonia trapped under the eyelids must be flushed out with water or it will continue to burn the eyeball and related tissues.

Lungs

At low concentrations the odor of anhydrous ammonia will usually 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 naturally be attracted to that part of the body. When a concentrated level of anhydrous ammonia is inhaled it will quickly burn the respiratory system. It may hurt too much to breathe. The respiratory system may essentially be paralyzed due to the pain.

Table 2. Exposure Levels and The Human Body

-------------------------------------------------
Exposure   Effect on 		Permissible 
(ppm)	   The Body		Exposure
-------------------------------------------------
50 ppm     Detectable by most 	No injury from 
	   people		prolonged, or
				repeated exposure

134 ppm    Irritation of nose 	Eight hours, 
	   and throat		maximum exposure

700 ppm    Coughing, severe 	One hour, 
	   eye irritation,	maximum exposure
	   may lead to loss
	   of sight

1700 ppm   Serious lung 	No exposure 
	   damage, death  	permissible
	   unless treated

2000 ppm   Skin blisters and 	No exposure 
	   burns within 	permissible
	   seconds

5000 ppm   Suffocation within 	No exposure 
	   minutes		permissible
-------------------------------------------------

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 to the scene. It may be difficult to maintain adequate respiration until delivery to a medical facility.

Respiratory protection is extremely important but also limited in regard to what equipment is available. A two-cartridge respirator is only effective for exposure levels of less than 300 parts per million. 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.

First Aid Calls For Water + Water + Water

When someone is exposed to anhydrous ammonia start first aid treatment immediately. The chemical burning starts instantly and the injury becomes worse as time passes. Treatment consists of flushing the affected body area(s) with lots 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 only 7� minutes. Additional water should be carried on every tractor used in field application and every field support motor vehicle. Collect as much water as possible and continue flushing while arrangements are being made for transportation to medical help. Do not reuse the water; it will not provide relief, having already absorbed anhydrous ammonia.

Transport To Medical Facility

Make arrangements to transport the victim to a doctor or hospital immediately after the 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.

Uncontrolled Releases

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. Ammonia vapors may pose a threat to farm houses and other residences. 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 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.

Protective Equipment for Anhydrous Ammonia

Due to the seriousness of exposure to anhydrous ammonia, personal protective equipment must be well maintained. This includes unvented goggles, rubber gloves, respirator, heavy-duty long-sleeved shirt, and long pants.

The goggles and gloves are to be kept in a safety equipment container mounted on each nurse tank, accessible from the ground. It is an excellent idea to have another set readily available on the tractor. Suitable gloves are made of rubber, are impervious to ammonia, and have long cuffs which should be turned back to prevent drips from running down the arm when hands are elevated. The fit should be loose enough for easy removal but snug enough for good protection.

Goggles must be unvented to keep the anhydrous ammonia away from the eyes. Only the un-vented type of goggles will minimize ammonia exposure to the eyes. Pesticide-type vented goggles are not suitable because ammonia can pass through the indirect vents. Open-vented shop goggles should never be used!

A respirator equipped with anhydrous ammonia cartridges approved by the National Institute for Occupational Safety and Health (NIOSH) is designed only for low level exposures not to exceed more than 300 parts per million. They do not have the capacity to protect a person from high level exposures.

Clothing should be heavy duty and of a tightly woven fabric. Light weight thin fabrics will not slow down or prevent anhydrous ammonia from passing through. The clothing should be tightly closed at the cuffs and collar to restrict the entry of anhydrous ammonia.

Five gallons of fresh, clean water are to be kept in the emergency water reservoir on the nurse tank and accessible from the ground, according to North Dakota Century Code. Another 5 gallons should be maintained on the tractor for use when the nurse tank water may not be easily accessible or runs out. This water should be changed daily to keep it clean. Dirty water may not flow through the reservoir hose, preventing treatment of the exposure.

Every worker should carry a 6 or 8 ounce plastic squirt bottle in their shirt pocket for immediate flushing of the eyes. It is to be used for the first flushing of the ammonia from the eyes and is intended to give the victim time to get to the 5 gallon supply.

Protective Equipment For Bulk Storage Facilities

Additional protective equipment is required for bulk storage of anhydrous ammonia. A rainsuit and two canister type gas masks are required by law in the North Dakota Century Code (Figure 1). 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.

Figure 1. Emergency Equipment (for Escape Only) (5KB b&w illustration)

If a major leak should occur, call your local fire department. They have self-contained breathing apparatus (SCBA) and protective suits. The SCBA supplies the air the wearer breathes, and not simply filter it as the respirators (cartridge and canister types) can only do. The protective suits are sealed to keep out anhydrous ammonia.

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

Keep the informative decals on the equipment up to date. These decals tell what each system component does and identifies the first aid water and protective measures.

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.

Nurse Tank Safety Check

Bleeder Valves

The bleeder valve is used to bleed or drain pressurized anhydrous ammonia from a closed hose or valve (Figure 2). 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.

Figure 2. Bleeder Valve (3KB b&w illustration)

Nurse Tank Hose

The nurse tank hose is subject to a lot of abuse, so it must be inspected on a daily basis. It must be maintained in safe condition since it transfers anhydrous ammonia under high pressure from the nurse tank to the applicator toolbar. 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 (Table 3, Nurse Tank Hose Safety Checklist).

Table 3. Nurse Tank Hose Safety Checklist*

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 2 years from date of manufacture, with nylon/kevlar for 4 years from date of manufacture, with stainless steel for 6 years from date of manufacture (Figure 3).

Figure 3. Nurse Tank Hose (4KB b&w illustration)

The nurse tank hose should always 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 flatten out. 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 from 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 which may cause a hose failure.

Nurse Tank

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 (Figure 4).

Figure 4 – Applicator Tank and Valves (7KB b&w illustration) – Nurse Tank and Valves (9KB b&w illustration)

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 percent of the surface may be corroded or missing paint.

There should be an Acme "parking fitting" for the nurse tank hose 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 correctly labeled on each end and side with the green diamond , DOT "NON-FLAMMABLE 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 kit must be complete with protective gloves and goggles. 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.

Table 4. Nurse Tank Safety Checklist

[ CONTINUE ]

[ 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 ]
[ Summary ] [ References ]

AE-1149, August 1998