By Yevhen Kovalchuk · Updated November 6, 2026 · 6 min read
Short answer
Ammonia (R-717) is an efficient, low-cost natural refrigerant with a strong odor that gives early warning of a leak. It is also toxic and, in a narrow range, flammable, so safe use depends on detection, ventilation, trained people and written emergency procedures. The OSHA exposure limit is 50 ppm as an 8-hour average, and facilities should confirm all values against their safety data sheet.
Ammonia, refrigerant number R-717, is a widely used industrial refrigerant that is efficient and has no ozone depletion or direct global warming potential. It is also toxic to breathe, corrosive to eyes and skin, and flammable in a narrow range. Its sharp odor lets people notice a leak at low levels, which is a real safety benefit, but it does not replace gas detection, ventilation and training. For the system layout, see ammonia refrigeration system basics.
What are the key properties of R-717?
| Property | What it means in practice |
|---|---|
| Chemical formula | NH3, a gas at normal conditions |
| Normal boiling point | About -28°F at atmospheric pressure |
| Refrigerant class | Natural refrigerant, no ODP and no direct GWP |
| Heat transfer | Very high latent heat, so less refrigerant circulates for a given load |
| Safety class | ASHRAE B2L: higher toxicity, lower flammability |
| Material compatibility | Attacks copper and copper alloys; steel is used instead |
| Water | Dissolves readily in water, which is useful in some emergency responses |
These values are standard published figures. Always confirm them against the safety data sheet for the product in your plant. The comparison with fluorocarbons is covered in ammonia vs Freon refrigeration.
How toxic is ammonia and how does the odor help?
Ammonia irritates the eyes, nose, throat and lungs. At higher concentrations it can burn tissue and cause serious breathing injury. OSHA lists a permissible exposure limit of 50 ppm as an 8-hour time-weighted average, and NIOSH lists a much higher level, 300 ppm, as immediately dangerous to life or health. Those thresholds are the reason many plants use alarms well below them.
The odor is sharp and noticeable at low concentrations, so workers often detect a small leak before instruments do. Do not rely on this alone: people can adapt to the smell, and it varies between individuals.
Is ammonia flammable?
Ammonia can burn or explode only within a flammable range in air, usually given as roughly 15% to 28% by volume. That is far higher than the concentration that causes injury, so a leak is a health hazard long before it is a fire hazard. The risk rises in an enclosed room with a large release and an ignition source, which is why machinery rooms are designed to prevent buildup. Ammonia is also hard to ignite and does not sustain a flame easily outside its range, which is why it is classed B2L.
What protections are normally in place?
A typical ammonia facility has layered protections:
- Fixed gas detection in the machinery room and other key areas, with alarms at defined levels and links to ventilation.
- Emergency ventilation that starts on alarm and is sized for the room, as required by the applicable code.
- Pressure relief and discharge arranged so relief valves vent safely.
- Emergency shutoff and stop controls at the machinery room entrance.
- Eyewash and safety shower stations near areas where liquid or concentrated ammonia could contact people.
- Signage and labeling of piping and equipment, and marked exits.
- Written procedures, training and drills for operators and emergency responders.
Large systems may also fall under OSHA Process Safety Management and EPA Risk Management Program rules, covered in OSHA PSM and EPA RMP for ammonia facilities. Industry practice is set by IIAR standards; see IIAR 2 and IIAR 6 explained.
What personal protective equipment is used?
PPE depends on the task and the expected exposure, and the facility’s hazard assessment decides it. Common elements include:
- Eye protection: chemical splash goggles, and a face shield for some tasks.
- Chemical-resistant gloves and clothing for work that could involve liquid ammonia.
- Respiratory protection: an escape respirator or a mask with ammonia-rated cartridges for limited exposure, and self-contained breathing apparatus for responders entering a release.
- Appropriate footwear and protection against cold burns, since liquid ammonia releases can freeze skin.
Respirator use requires fit testing, training and a written program under OSHA rules.
What are the emergency basics?
Every plant should have an emergency action plan that reflects its own layout. The general principles are:
- Leave and alert. People move away from the release, upwind and out of low areas, and raise the alarm.
- Do not enter without training and equipment. Only trained responders with the right protection should enter a release area.
- Shut down and isolate the source if it can be done safely, using the designated emergency controls.
- Call for help early, including the fire department and, when required, the proper reporting authorities.
- Treat exposure at once. Flush eyes and skin with plenty of water and get medical care.
- Review afterward and correct the cause.
A drill that uses the real alarms and the real exit routes is worth more than a binder on a shelf.
Frequently asked questions
Can you smell ammonia before it is dangerous?
Usually yes, because the odor is noticeable at low concentrations. But smell is not a safe measure of exposure, as nose fatigue and individual differences are real. Fixed detectors and alarm setpoints are the proper control.
Is ammonia safe to use in a commercial building?
It is used widely in industrial settings with controls and trained staff. In public spaces, codes limit the amount and location, and many designers use ammonia only in a separate machinery room or in low-charge systems. See CO2 transcritical refrigeration for another natural-refrigerant option.
What does the safety class B2L mean?
ASHRAE uses the letter for toxicity, with B meaning higher toxicity at lower exposure limits, and the number and L for flammability, with 2L meaning lower flammability and a low burning velocity. Ammonia is B2L.
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