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NH3 Gas and its Sensor

Intro to Ammonia

Ammonia gas is a chemical compound with the chemical formula NH3 so the ammonia molecule is comprised of one nitrogen atom and three hydrogen atoms. It is a colorless gas, but is easily identifiable by smell, as it has a pungent odor. Ammonia gas is commonly found in the production of fertilizers and refrigerants, however you are likely to smell it well before it will be harmful to you. The degree of danger that ammonia gas poses varies significantly depending on how much is present, and how long you've been exposed for. 

Gas Characteristics

  • Colorless
  • Gas state
  • Compressed
  • Toxic
  • Flammable
  • Corrosive
  • Lighter than air
  • Water soluble
  • Explosive (at high concentrations and confined spaces)
  • Pungent, suffocating odor
  • Can decompose at high temperatures forming very flammable hydrogen gas
  • OTHER NAMES: Anhydrous ammonia, ammonia, azane, hydrogen nitride
  • CAS 7664-41-7
icon ghs flammable - examples include nitrogen oxides, concentrated ammonia solutions, anhydrous ammonia
icon ghs toxic - examples include nitric acid which can dissolve alkali metals and cause harm to the respiratory tract of workers along with ammonium chloride
GHS corrosive WHMIS - examples include sulphuric and nitric acids including ammonium hydroxide

Industrial NH3 hazards and sources

  • Farms: Ammonia produced by compost piles on mushroom farms can generate ammonia gas. Manure pits and any indoor or confined spaces where farm animals are kept can also contain ammonia gas.
  • Refrigeration Systems: Ice rinks and ice manufacturing plants use liquid ammonia. If it leaks, it becomes a gas.
  • Fertilizers and Cleaners: Liquid ammonia is often diluted and combined with other chemicals.
  • Some manufacturing processes also use ammonia.
  • May be exposed to ammonia while using cleaning products that contain ammonia.
  • Other sources of occupational exposure include the silvering of mirrors, gluemaking, tanning of leather, and around nitriding furnaces.
  • Ammonia is produced as a by-product in coal distillation and by the action of steam on calcium cyanamide, and from the decomposition of nitrogenous materials.
  • Ammonia naturally occurs in soybean (8,600 ppm), evening-primrose seeds (2,300–2,455 ppm), lambsquarter, and tobacco leaves (Duke, 1992).

Ammonia leaks are on the rise due to increased use of natural refrigerants over fluorinated gas counterparts.

(Process Equipment & Control News)

High Risk Scenarios

  • Ammonia concentrations are generally higher in warm buildings than cold buildings.
  • In an enclosed space, ammonia can explode if an ignition source is introduced.
  • Outside of an accidental release of ammonia, the potential for exposure to high concentrations of ammonia is greatest during confined space entry.
  • Technically speaking, the moment a worker breaks the plane of an opening, he or she has in fact entered a confined space, and when ammonia is involved, workers should assume that confined spaces present a hazardous environment.
  • In the event of a leak or CSE procedure, it would be a mistake to assume that ammonia’s distinct odor would serve as an adequate warning signal.
  • Gas detectors can measure the concentrations of ammonia and can quickly alert workers of changes in air quality.

NH3 Sensor Info

Type: Electrochemical
Range: 0-100 ppm (0.1 ppm resolution)
High Range: 0-500 ppm (1 ppm resolution)

Default Alarm Levels

Low Alarm: 25 ppm
High Alarm: 50 ppm
STEL — 15 minute — Short Term Exposure Limit: 35 ppm 
TWA  — 8 hour time weighted average: 25 ppm 

Blackline devices that can detect NH3

Questions about the detection of NH3?


Special Applications and Considerations

  • Slow-moving water: Slow-moving or stagnant water may have high ammonia concentrations because of lack of turbulence and volatilization and greater accumulation of metabolic waste and decomposition products—including ammonia (WHO 1986).
  • High density of fish: Reduced stream flow may concentrate fish into pools or other refugia, concentrating waste excretion and elevating ammonia concentrations.
  • Presence of organic wastes: Organic wastes are the remains of any once-living organism or their excrement. Excrement and sewage are high in ammonia, so signs of such material in a waterbody may suggest ammonia as a candidate cause. In contrast, plant material is typically low in nitrogen, and associated decomposers may take up ammonia and reduce its aqueous concentration. Identifying the type of organic waste present in a waterbody will aid in identifying candidate causes. Excessive organic wastes in water may result in a grayish cast with visible sludge deposits in depositional areas.
  • Foul odor: Ammonia as a gas has a characteristically pungent odor (think of window and floor cleaners). Ammonia concentrations in streams are rarely high enough to exhibit this odor, but water that has a foul, septic or organic-waste smell may have relatively high concentrations of ammonia.
  • Suspended solids: Suspended solids from wastewater effluents or runoff can contain high ammonia or act as catalysts for bacterial growth promoting accumulation of ammonia. Identifying the type of suspended material present is important in identifying candidate causes.
  • Alkaline, anoxic, or warm water: Water characteristics that promote ammonia formation (e.g., anoxia) or increase toxicity (e.g., high pH and temperature) are signs that ammonia may be a cause.
  • You can taste ammonia in water at levels of about 35 ppm

Health Risks and Handling of NH3

0 - 0.5
Typical background concentrations
0.6 - 23
Can usually be detected by smell
24 - 29
Nose and throat irritation can occasionally be detected (2-6 hours of exposure)
30 - 49
Slightly irritating to some people after 10 minutes of exposure
50 - 71
Moderately irritating to the majority of people after 10 minutes of exposure
72 - 139
Irritation of the nose and throat can occur after only 5 minutes of exposure
140 - 499
Will be unbearably irritating to most people after 30 minutes
500 - 1499
Nose and throat will immediately experience severe irritation, lacrimation occurs (crying)
1500 - 2499
Brief exposure can lead to a pulmonary edema (accumulation of fluid in the lungs, potentially fatal)
2500 - 4500
Death likely after 30+ minutes of exposure
5000 +
Will often cause rapid respiratory arrest, death very likely
  • Inhalation: Take precautions to ensure your own safety before attempting rescue (e.g., wear appropriate protective equipment). Move victim to fresh air. If breathing is difficult, trained personnel should administer emergency oxygen. DO NOT allow victim to move about unnecessarily. Symptoms of pulmonary edema may be delayed. Immediately call a Poison Centre or doctor. Treatment is urgently required. Transport to a hospital.
  • Skin Contact from Gas: flush with lukewarm, gently flowing water for 5 minutes. If irritation or pain persists, see a doctor. 
  • Eye Contact from Gas: immediately flush the contaminated eye(s) with lukewarm, gently flowing water for 5 minutes, while holding the eyelid(s) open. If irritation or pain persists, see a doctor. 
  • Handling: Immediately report leaks, spills, or failures of the safety equipment (e.g., ventilation system). In event of a spill or leak, immediately put on escape-type respirator and exit the area. Do NOT work alone with this product. Get medical attention for all exposures. Symptoms can be delayed. Prevent accidental contact with incompatible chemicals.


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