Anhydrous ammonia (NH3) is one of the leading sources of nitrogen fertilizer applied to agricultural crops in the U.S. because, by molecular weight, it is 82% nitrogen, readily available and easy to apply. There are, however, disadvantages and potential dangers involved in handling and using anhydrous ammonia.
Ammonia gas is compressed into a liquid for storage and use. Ammonia is stored and handled under pressure, which requires the use of specially designed and well-maintained equipment. At 60° F ammonia has a vapor pressure of 93 psi; at 100° F the vapor pressure is 200 psi. As the temperature of the ammonia rises, so does the vapor pressure.
Liquid anhydrous is a very cold liquid, with a boiling point of -28° F, but a high-pressure flashing liquid release can produce temperatures of -60° F or lower and cause serious thermal burns very quickly. Liquid ammonia, when released, quickly returns to the gas state at the expansion rate of 850 gallons of ammonia gas for every gallon of liquid. Additionally, employees of suppliers, end users and emergency responders must be adequately educated about the procedures and personal protective equipment (PPE) necessary to safely handle and work around anhydrous ammonia.
Because anhydrous ammonia is so common in many parts of the country, complacency may develop during dispensing, transportation and use. Anhydrous ammonia is primarily transported in rural areas from a distributor to a farm in nurse/applicator tanks usually pulled behind farm pickup trucks (a nurse tank is a container that is used only for transporting anhydrous ammonia.). The liquid capacity of these tanks ranges from 1,000 to 3,000 gallons and it is that more than 200,000 of these tanks are in use nationwide. During filling, the tanks are required to be no more than 85% full of ammonia.
Some nurse tank trailers are equipped with two tanks on the same trailer. State laws control the number of trailers that can be towed at one time over public roads and the speed of travel. The number of nurse tanks allowed to be towed ranges from one to three, depending on state law. Ammonia nurse tanks are required to have a minimum of five gallons of water on the nurse tank, which is usually in a red plastic tank on top of the nurse tank. This water is used for emergency flushing of the eyes or body when a person has come in with ammonia.
Anhydrous ammonia is classified by the U.S. Department of Transportation (DOT) as a Class 2.2 Non-flammable Gas. Unfortunately, this classification leaves three other important hazards of anhydrous ammonia unidentified by the DOT placard and labeling system. Not only will anhydrous ammonia burn under certain conditions, it is classified as a caustic (corrosive) liquid and poison gas in other parts of the world. Material safety data sheets (MSDS) from manufacturers of anhydrous ammonia in the U.S. identify its hazards as flammable, toxic and corrosive.
Anhydrous means “without water.” Anhydrous does not apply to just ammonia, as other chemicals may also have the term anhydrous in their name and it has the same meaning the same thing. Thus, anhydrous ammonia is a colorless, liquefied compressed gas that is free of water. Because anhydrous is free of water, it has a high affinity for water. Thirteen hundred gallons of ammonia vapor will dissolve in just one gallon of water. Ammonia has a very sharp, intensely irritating odor – anyone in the area of a release will not want to stay! Ammonia is corrosive to galvanized metals, copper and copper alloys.
Ammonia gas is lighter than air, but also very close to the weight of air with a density of 0.6, so cold vapors or dense aerosol clouds may stay close to the ground or in low lying areas. It has an auto ignition temperature of 1,204° F and a flammable range of 16-25%. DOT does not classify ammonia as flammable gas because it does not meet the definition used for flammable gases.
According to DOT, a flammable gas has a lower explosive limit below 13 or a flammable range of greater than 12 percentage points. Ammonia misses the definition on both counts. Ammonia has a lower explosive limit of 16, 3 points above the DOT requirement for flammable gas and the flammable range is 10 percentage points, not the 12 required by DOT’s definition. It does, however burn when it ignites, and has caused injury and two known firefighter fatalities. Normally, ammonia needs to be inside of a building or confined space to ignite. It does not usually burn outside in the open. However, during a tanker crash in Sacramento, CA, ammonia trapped under an overpass did ignite.
Anhydrous ammonia is considered to be toxic with a National Institute for Occupational Safety and Health (NIOSH) Immediately Dangerous to Life and Health (IDLH) of 300 ppm in air. According to the U.S. Centers for Disease Control and Prevention (CDC) inhalation of concentrated fumes at the rate of 5,000 to 10,000 ppm for short periods may be fatal. Additionally, exposure to 2,500 to 6,000 ppm for 30 minutes or greater are considered dangerous to life. Responders will require appropriate personal protective equipment (PPE), including chemical protective clothing and self-contained breathing apparatus (SCBA) to protect themselves or to perform rescue. Most reference sources recommend Level A gas/vapor suits for chemical protection. Chemical protective clothing is not usually readily available to most rural departments.
In March 2014, a release of anhydrous ammonia occurred at the Midwest Farmers Cooperative facility in Tecumseh, NE. An anhydrous ammonia semi-transport driven by an employee of Midwest had been positioned at the ammonia bulk plant in preparation for off-loading the liquid ammonia into the bulk plant. During the off-loading process, an explosion reportedly occurred that resulted in the release of approximately 100 pounds into the atmosphere. One employee of Midwest was killed and three other people were injured, including a deputy sheriff.
Anhydrous ammonia is considered an extremely hazardous substance by the Environmental Protection Agency (EPA) and releases of 100 pounds or more must be reported to the National Response Center (NRC) within 24 hours. Common procedure at anhydrous ammonia fertilizer facilities is to vent hoses with ammonia liquid or vapor into a plastic or steel bleed-off water tank to absorb ammonia into the water. Typical plastic tanks have a 275-gallon liquid capacity with a cap on top, but are not pressure tanks. By venting the ammonia into the water, the amount released into the air is minimal. This process, while legal, has its hazards and limitations. First, there is a physical limit to the amount of ammonia that can be absorbed into the water. A gallon of water will only absorb only one to two pounds of ammonia before the water becomes saturated. If the water in the tank is not changed once saturation occurs, little additional liquid or vapor can be absorbed. This may result in over-pressurization of the tank, which may result in an explosive tank failure if the tank is not vented. Second, when ammonia is absorbed by water, a caustic chemical called ammonium hydroxide, or aqua ammonia, is formed. This liquid is very corrosive to skin and can cause serious chemical burns. Initial reports about the incident in Tecumseh indicated an explosion had occurred resulting in the release of the ammonia vapors.
An investigation by the Nebraska State Fire Marshal’s Office resulted in the following conclusions.
1. The bleed-off valve on the liquid valve at the load-in bulkhead was accidently left in the open position when the liquid and vapor hoses from the semi-transport were connected.
2. When the primary liquid valves were opened and the transport pump was started, high-pressure liquid anhydrous ammonia was allowed to enter the plastic bleed-off water tank through the open bleed-off valve.
3. This high-pressure liquid anhydrous ammonia vaporized within the plastic water container, which led to an over-pressurization and eventually an explosive rupture of the container. In addition, this type of plastic container was not designed to be capable of holding pressure as a pressure vessel. It should be noted also that there is no regulatory requirement that the bleed-off water tank be a pressure vessel or that the tank be vented.
4. Once the container was destroyed, the liquid anhydrous ammonia was free to vaporize and escape to the atmosphere, creating a vapor cloud.
5. This anhydrous ammonia release continued until an employee was able to close the bleed-off valve.
Mild exposure to anhydrous ammonia can cause irritation to eye, nose and lung tissues. When NH3 combines with moisture in the lungs, it causes severe irritation. Ammonium hydroxide is actually produced in the lungs. Prolonged breathing of high ammonia concentrations can severely damage lung tissue and cause suffocation.
The human eye is a complex organ made up of nerves, veins and cells. The front of the human eye is covered by membranes that resist exposure to dust and dirt, but none of these can keep out anhydrous ammonia, because the entire eye is about 80% water. A shot of ammonia under pressure can cause extensive, almost immediate damage to the eye. Ammonia extracts the fluid and destroys eye cells and tissue in minutes. If you get a shot of anhydrous ammonia in your eye, the first few seconds are crucial. Immediately flush the eyes with copious amounts of water. If wearing contact lenses (contacts are NOT recommended when working with ammonia), remove them. Your eyes will fight to stay closed because of the extreme pain, but they must be held open so the water can flush out the ammonia. Eyes doused with ammonia close involuntarily. They must be forced open so water can flush the entire eye surface and inner lining of the eyelids. Continue to flush the eyes for at least 15 minutes. Get professional medical help as soon as possible to prevent permanent damage. If water is not available, fruit juice or cool coffee can be used to flush the eyes. Remove contaminated clothing and thoroughly wash the skin.
Clothing frozen to skin by liquid ammonia can be loosed with liberal application of water. Wet the clothing and body thoroughly and then remove the clothing. Never put an exposed victim into an ambulance without first thoroughly decontaminating them and any clothing with copious amounts of water. Leave burns exposed to the air and do not cover with clothing or dressings. Immediately after first-aid treatment with water, get the burn victim to a physician. Do not apply salves, ointments or oils – these cause ammonia to burn deeper. Let a physician determine the proper medical treatment.
Remove the victim to an area free from fumes. If the patient is overcome by ammonia fumes and stops breathing, get them to fresh air and give artificial respiration. The patient should be placed in a reclining position with head and shoulders elevated. Basic life support should be administered if needed. Oxygen has been found useful in treating victims who have inhaled ammonia fumes. Administer 100% oxygen at atmospheric pressure. Any person who has been burned or overcome by ammonia should be placed under a physician’s care as soon as possible. Begin irrigation with water immediately. The rescuer should use fresh water if possible.
If the accident occurs on a farm, be aware that there is a requirement for water tanks for irrigation of the eyes and body on the anhydrous ammonia tank. Open water in the vicinity of an anhydrous ammonia leak may have picked up enough NH3 to be a caustic aqua ammonia solution. This could aggravate the damage if used in the eyes or for washing burns. The victim should be kept warm, especially to minimize shock. If the nose and throat are affected, irrigate them with water continuously for at least 15 minutes. Take care not to cause the victim to choke. If the patient can swallow, encourage drinking lots of some type of citrus drink such as lemonade or fruit juice. The acidity will counteract some of the affect of the anhydrous.
Responding to anhydrous ammonia emergencies can present many challenges to emergency responders. Ammonia is a colorless gas, so there may not be any visual indications of where the gas is. There are things to watch for. Ammonia gas will quickly turn vegetation brown. If it’s a time of year where the vegetation is expected to be green, then watch for brown vegetation. You can also watch for an animal or bird kill, which may have resulted from exposure to the ammonia gas in a release.
Ammonia also has a strong odor; you can smell it before reaching a lethal dose. The odor threshold is 5-20 ppm, well below dangerous levels. However, as with all hazardous materials, responders should not be in a position to smell materials. Firefighter turnouts do not provide protection from ammonia gas or liquid. SCBA will protect the respiratory system.
Ammonia vapors will seek out locations on the bodies of responders where there is moisture. The eyes are a major concern as they can be damaged or blindness can occur from ammonia contact. Areas in the groin and armpits are also potential moisture spots. However, firefighters in full turnouts can sweat and moisture can be present on any part of the body, depending on ambient temperatures. First responders in firefighter turnouts should avoid contact with ammonia vapors or liquid.
Because of its great affinity to water, first responders can use hose streams to decontaminate victims exposed to ammonia vapors or liquid. They can also use fog streams to dissolve ammonia gas from the air to protect victims or those in harm’s way. Remember, however, water and ammonia form ammonium hydroxide, a corrosive liquid – after victims receive emergency decontamination, efforts should be made to control the runoff.
Anhydrous ammonia can cause corrosion on some metals, particularly copper, brass or galvanized steel. Many parts of fire apparatus and firefighting equipment are made of brass, which can be damaged if in contact with anhydrous. Like anhydrous ammonia, liquid petroleum gas (LPG) is stored in the same type of steel tanks. A high percentage of agricultural anhydrous ammonia accidents are the result of using improper procedures, lack of training in equipment operation or failure to follow prescribed practices. Emergency responders can avoid additional injuries and death with the proper planning, training and equipment to effectively handle agricultural ammonia emergencies.
Thanks to the Nebraska State Fire Marshal’s Office for the report and photographs of the Tecumseh incident. Also thanks to Kent Anderson, chair of the Ammonia Safety and Training Institute (ASTI), for his technical support during the fact-finding and preparation of this article. ASTI has developed a set of Emergency Response Cards to assist emergency responders in handling releases of anhydrous ammonia and regularly does training for fire departments, hazmat teams and industry.
