Properties of Ammonia
 Ammonia |
Ammonia is a chemical consisting of one atom of nitrogen and three atoms of hydrogen. It is designated in chemical notation as NH3. Ammonia is extremely soluble in water and is frequently used as a water solution called aqua ammonia. Ammonia chemically combines with water to form ammonium hydroxide. Household ammonia is a diluted water solution containing 5 to 10 percent ammonia. On the other hand, anhydrous ammonia is essentially pure (over 99 percent) ammonia. "Anhydrous" is a Greek word meaning "without water;" therefore, anhydrous ammonia in ammonia without water.
Refrigerant grade anhydrous ammonia is a clear, colorless liquid or gas, free from visible impurities. It is at least 99.95 percent pure ammonia. Water cannot have a content above 33 parts per million (ppm) and oil cannot have a content above 2 ppm. Preserving the purity of the ammonia is essential to ensure proper function of the refrigeration system.
- Keeping Ammonia Pure
- Physical Properties
- Chemical Properties
- Health Effects
| Keeping Ammonia Pure |
Impurities can enter the ammonia system:
Potential Hazards:
Possible Controls:
Additional References:
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| Physical Properties | ||||||||||||||||||||||
Anhydrous ammonia is a clear liquid that boils at a temperature of -28°F. In refrigeration systems, the liquid is stored in closed containers under pressure. When the pressure is released, the liquid evaporates rapidly, generally forming an invisible vapor or gas. The rapid evaporation causes the temperature of the liquid to drop until it reaches the normal boiling point of -28°F, a similar effect occurs when water evaporates off the skin, thus cooling it. This is why ammonia is used in refrigeration systems. Liquid anhydrous ammonia weighs less than water. About eight gallons of ammonia weighs the same as five gallons of water. Liquid and gas ammonia expand and contract with changes in pressure and temperature. For example, if liquid anhydrous ammonia is in a partially filled, closed container it is heated from 0°F to 68°F, the volume of the liquid will increase by about 10 percent. If the tank is 90 percent full at 0°F, it will become 99 percent full at 68°F. At the same time, the pressure in the container will increase from 16 pounds per square inch (psi) to 110 psi. Liquid ammonia will expand by 850 times when evaporating: Anhydrous ammonia gas is considerably lighter than air and will rise in dry air. However, because of ammonias tremendous affinity for water, it reacts immediately with the humidity in the air and may remain close to the ground. The odor threshold for ammonia is between 5 - 50 parts per million (ppm) of air. The permissible exposure limit (PEL) is 50 ppm averaged over an 8 hour shift. It is recommended that if an employee can smell it they ought to back off and determine if they need to be using respiratory protection. Summary of properties:
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| Chemical Properties |
Anhydrous ammonia is easily absorbed by water. At 68°F, about 700 volumes of vapor can be dissolved in one volume of water to make a solution containing 34 percent ammonia by weight. Ammonia in water solution is called aqua ammonia or ammonium hydroxide. Ammonia, especially in the presence of moisture, reacts with and corrodes copper, zinc, and many alloys. Only iron, steel, certain rubbers and plastics, and specific nonferrous alloys resistant to ammonia should be used for fabrications of anhydrous ammonia containers, fittings, and piping. Ammonia will combine with mercury to form a fulminate which is an unstable explosive compound. Anhydrous ammonia is classified by the Department of Transportation as nonflammable. However, ammonia vapor in high concentrations (16 to 25 percent by weight in air) will burn. It is unlikely that such concentrations will occur except in confined spaces or in the proximity of large spills. The fire hazard from ammonia is increased by the presence of oil or other combustible materials. Anhydrous ammonia is an alkali. |
| Health Effects |
Ammonia is not, strictly speaking, a poison and repeated exposure to it produces no additive (chronic) effects on the human body. However, even in small concentrations in the air it can be extremely irritating to the eyes, throat, and breathing passages. Anhydrous ammonia primarily affects three areas of the body:
Eyes Everything from mild irritation to destruction of the eye can occur depending on whether a spray or gas is involved. Ammonia penetrates the eye more rapidly than other alkalis. Lungs In the lungs, liquid anhydrous ammonia causes destruction of delicate respiratory tissue. Exposure to ammonia vapor may cause:
Skin Skin damage depends upon the length and concentration of exposure and can range from mild irritation, to a darkened freeze-dry burn, to tissue destruction. Because liquid ammonia boils at -28°F, the expanding gas has the potential to freeze anything in its path of release, including human flesh and organs. Because water can absorb ammonia so readily, it is a factor that contributes to human toxicity. Ammonia will keep spreading across contacted skin until the chemical is diluted by skin moisture. Alkalis effect tissue differently than acids, which tend to burn and seal off a wound. Alkalis, such as ammonia cause liquidization of tissue and turn tissue into a sticky "goo" and mix with this tissue, causing further damage. As a result, anhydrous ammonia burns keep spreading until the chemical is diluted. In addition to liquidization, super-cooled anhydrous ammonia spray causes a freeze dry effect like frost bite when it hits the skin. The spray is also capable of freezing clothing to skin so that if the clothing is removed incorrectly whole sections of skin can be torn off. High concentrations in the air can also dissolve in the moisture of the skin or perspiration and result in a corrosive action on the skin and mucous membranes. First Aid Decontaminate the victim as quickly as possible.
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