Anhydrous ammonia, or ammonia that lacks water, is an incredibly important chemical for agriculture. Containing one part nitrogen and three parts hydrogen, ammonia is a source of nitrogen for many commercial fertilizers, and anhydrous ammonia can be directly applied to crop soil after it has been pressurized to maintain a liquid composition. To prevent vaporization, the compressed gas is injected into the soil. Anhydrous ammonia has several other applications, being used for a variety of purposes in laboratory testing.
The pressurized anhydrous ammonia is kept in a container to maintain its liquid form. The exact design pressure varies from system to system, but the minimum design pressure, according to ANSI/CGA G-2.1-2014 - Requirements for the Storage and Handling of Anhydrous Ammonia, is 250 psi. Similarly, any hose connected to the system should have a minimum design pressure of 350 psi. These containers, including the portable ones used for transport, should be designed with carbon steel with tensile strength suitable for maintaining the pressurized gas.
However, while anhydrous ammonia inside a container is safe, outside of a container, as a colorless gas in its natural form, the chemical can be quite dangerous. At lower concentrations, ammonia gas is irritating to the eyes, skin, and mucous membranes of the nose, throat, and lungs. At higher concentrations, its effects become far more severe, as anhydrous ammonia is corrosive to human tissue. ANSI/CGA G-2.1-2014 describes the effects of ammonia on the human body from specific concentrations in the following table:
To combat problems related to direct contact with anhydrous ammonia, it is recommended that employers provide ammonia installations with clean, running water for emergency use, or emergency eyewash units. In the event of exposure to the eyes or skin, ANSI/CGA G-2.1-2014 states that the exposed area should be "flushed with clean water for at least 15 minutes or more (preferably 20-30 minutes but not less than 15 minutes), with the eyes receiving first attention.”
When anhydrous ammonia comes in contact with any moisture, the water and ammonia rapidly combine. So, if ammonia meets the moisture of the human body, it can cause dehydration and other detrimental effects. If an individual has any ammonia enter his or her mouth or nostrils, he or she should be given large quantities of water to prevent any harm that the chemical could bring to his or her body.
Water can also be used to cool ammonia containers that have caught fire, or to reduce the concentration of ammonia vapor during the event of a release. However, water should never be used on liquid ammonia spills, as it can cause a chemical reaction. In the event of a container leak, small quantities of the ammonia can be absorbed by discharging into a vessel containing at least 1 gal (4 L) of water for every 1 lb (0.5 kg) of ammonia.
However, all of this exposure can be prevented by properly fitting workers with materials that prevent direct contact with anhydrous ammonia. Every worker should wear protective gloves, boots, pants, and jacket, all of which are impervious to ammonia.
While the guidelines for ammonia usage do not apply to those involved with its transport, drivers who transport anhydrous ammonia should still be adequately trained in understanding ammonia and any problems that might arise from a portable ammonia system. For example, in the event of a leak, as stated in the standard, “the driver should make every effort possible, including moving the vehicle to an isolated location downwind from populated communities or heavily traveled highways, to transfer the contents to another approved ammonia container.”
To assure competency in all things anhydrous ammonia, refresher training should be completed at least once every three years. This is necessary for any person required to “handle, transfer, transport, or otherwise work with ammonia.”
To address any concerns related with fire and potential explosions of anhydrous ammonia systems, ANSI/CGA G-2.1-2014 calls for the inclusion of pressure relief valves, which are also useful if the volume of the system’s gas content expands from rising heat.
Further guidelines are addressed in ANSI/CGA G-2.1-2014 - Requirements for the Storage and Handling of Anhydrous Ammonia, the American National Standard for the design, construction, repair, alteration, location, installation, and operation of anhydrous ammonia systems. This document is available on the ANSI Webstore.
1. The Compressed Gas Association, Inc., ANSI/CGA G-2.1-2014 - Requirements for the Storage and Handling of Anhydrous Ammonia (Chantilly: The Compressed Gas Association, Inc., 2014), 3.