5.1 Ammonia Properties, SDS, and Exposure Limits

Ammonia Is a Refrigerant and a Highly Hazardous Chemical

Quick Answer: Anhydrous ammonia in industrial refrigeration is R-717 (NH3). At 1 atm it boils at about -28°F (-33°C). It is highly soluble in water and corrosive to moist tissue. Dry, warm vapor is lighter than air; a cold or wet release can hug floors, pits, and basements. OSHA Table Z-1 PEL is 50 ppm as an 8-hour TWA. OSHA's ammonia refrigeration page cites IDLH 300 ppm, a flammable range of about 15–28% by volume, and an odor threshold of 20 ppm. NIOSH REL and ACGIH TLV are 25 ppm TWA / 35 ppm STEL — name the authority every time you quote a number.

The CIRO exam treats ammonia first as a chemical that can kill you, then as a refrigerant you can operate. This section is the chemical half: properties, the SDS in the on-screen references, and the exposure numbers that drive alarms, PPE, and first aid. Detection setpoints and emergency-switch hardware are applied in the next section using the same 25 ppm / 150 ppm / high-range ladder already taught from ANSI/IIAR 2-2021.

Identity and boiling behavior

Plant nameplates, P&IDs, and RETA texts say R-717. Chemists say NH3. PSM paperwork says ammonia, anhydrous, CAS 7664-41-7. Those labels are the same substance. It is not the dilute aqua ammonia in a janitorial bottle. Anhydrous means essentially no water in the charge. In the receiver it is a liquefied gas. When liquid hits atmospheric pressure it boils at about -28°F (-33°C) and takes a large amount of heat from anything it touches — skin, eyes, wet clothing, and carbon-steel pipe. The injury is both frostbite and an alkali chemical burn.

Because the boiling point is far below room temperature, a liquid-line spray does not puddle like water. It flashes, chills the remaining liquid and the surrounding air, and produces a white fog when the vapor mixes with moisture. Operators who only look for a colored gas will walk through a cloud.

Density: lighter than air — until it is not

Ammonia's molecular weight is about 17; dry air is about 29. Dry, warm ammonia vapor is lighter than air and tends to rise. High detectors and roof vents are not wasted hardware. The exam trap is stopping the story there.

A cold release is physically denser than the same gas at room temperature. Liquid droplets and a wet ammonium-hydroxide aerosol add mass. That mixture rolls into machinery-room trenches, elevator pits, basements, and low doorways and can stay there until it warms and mixes. The CIRO sentence is: lighter than air when dry and warm; can hug low areas when cold and wet. Search high and low. Do not send someone into a pit because ammonia always goes to the ceiling.

Solubility and corrosivity

Ammonia is highly soluble in water. Dissolved NH3 forms ammonium hydroxide, a strong alkaline corrosive. That single fact explains:

• Why a water spray knocks down an outdoor vapor cloud (the gas dissolves into the droplets).
• Why eyewash and safety showers are the first-aid tools, not neutralizing chemicals.
• Why moist tissues — eyes, lungs, mucous membranes, sweaty skin — are damaged faster than dry skin.
• Why runoff from a water curtain is still hazardous dilute aqua ammonia and must be contained, not dumped to a storm drain.

Ammonia is corrosive, not an acid. An operator who reaches for vinegar, citric acid, or muriatic acid to balance the pH on a burn is about to add a neutralization heat release to an alkali injury. SDS first-aid language is water, time, and medical care.

Odor, fire, and IDLH — use OSHA's refrigeration page

OSHA's ammonia refrigeration safety page is the public reference CIRO study materials echo. Use these figures when a question cites that OSHA page:

Odor is a gift and a trap. Twenty ppm sits below the OSHA PEL and near the NIOSH REL, so a trained nose can notice a leak. It is not a calibrated sensor, not a clearance to pull a respirator, and not proof a pit is clean. IIAR 2 puts detectors in the room because noses fail.

The flammable range is wide in percentage terms and still far above concentrations that already force evacuation. Do not tell a fire captain that ammonia does not burn. Do not treat a 200 ppm leak as a fireball. Treat ignition sources, hot work, and high-range shutdowns as the controls for the rare rich cloud.

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Exposure Limits — Write the Authority on the Same Line

Mixing OSHA, NIOSH, and ACGIH is a classic CIRO miss. The numbers sit close together and they are not the same legal object.

OSHA Table Z-1 PEL: 50 ppm, 8-hour TWA. 29 CFR 1910.1000 Table Z-1 is the enforceable Permissible Exposure Limit for ammonia: 50 ppm as an eight-hour time-weighted average. Table Z-1 does not list an OSHA STEL for ammonia. Averaging under 50 ppm across a shift does not authorize unprotected work at 80 ppm for twenty minutes.

NIOSH REL: 25 ppm TWA / 35 ppm STEL. The National Institute for Occupational Safety and Health Recommended Exposure Limit is 25 ppm time-weighted average and 35 ppm short-term exposure limit. NIOSH RELs are recommendations. Many plants still use 25 ppm as the investigation alarm because it matches NIOSH, ACGIH, and the IIAR 2 25 ppm monitored-location setpoint.

ACGIH TLV-TWA 25 ppm / TLV-STEL 35 ppm. The American Conference of Governmental Industrial Hygienists publishes Threshold Limit Values. Cite ACGIH when you quote them. They are not OSHA PELs.

150 ppm is one-half of 300 ppm IDLH. That arithmetic is why IIAR 2 latches emergency ventilation at ≥150 ppm. Do not invent a different half-IDLH. Do not call 50 ppm the NIOSH REL. Do not call 25 ppm the OSHA PEL.

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Using the On-Screen Ammonia SDS

CIRO on-screen references include an ammonia safety data sheet. The official study guide presents a Hill Brothers-style commercial SDS in the GHS 16-section format. You are not scored on copying a vendor footer. You are scored on opening the right section without CTRL+F (exam security can log you out) and applying it.

Focus on these sections:

• Section 2 — Hazard identification. Signal word (typically Danger), GHS pictograms, and hazard statements: toxic if inhaled, severe skin burns and eye damage, respiratory irritation, gas under pressure, and flammable gas in the right mixture. This is the what-can-it-do page.
• Section 4 — First-aid measures. Eyes and skin: flush with water at least 15 minutes, remove clothing and contacts during the flush, then medical care. Inhalation: fresh air, trained oxygen or resuscitation only, medical evaluation even if symptoms seem mild (pulmonary edema can lag). Do not neutralize with acids or other chemicals.
• Section 5 — Fire-fighting measures. SCBA for firefighters, water spray or fog to absorb vapor and protect exposures, cool containers, and remember ammonia burns in about the 15–28% window. Stopping the leak, if it can be done safely from outside the cloud, beats extinguishing a plume that then re-forms a flammable mixture.
• Section 6 — Accidental release measures. Evacuate downwind and low areas, deny entry, ventilate, isolate the source from outside the cloud, use water spray on vapor, and contain runoff. Do not inject water into a liquid-ammonia vessel as a dilution stunt — that can flash and overpressure equipment. Unprotected operators do not go find the hiss.
• Section 8 — Exposure controls / personal protection. This is where PEL, REL, and TLV rows often sit side by side. Read the authority column. Section 8 also lists ventilation and PPE: chemical splash goggles, face shield, ammonia-rated respiratory protection, chemical gloves, and clothing.

Related sections you should still be able to find: Section 1 identification (CAS 7664-41-7), Section 7 handling and storage, Section 9 physical and chemical properties (boiling point, vapor density, flammable limits), Section 10 incompatibles (including copper, zinc, and acids), and Section 14 transport (UN 1005 anhydrous ammonia). On a PSM-covered process the SDS is process safety information. The copy in the control room must match the refrigerant that is actually in the pipes.

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First Aid That Matches the SDS

Treat ammonia injury as a time-critical alkali burn plus inhalation injury:

1. Eyes. Hold the lids open and flush with water 15 minutes or more — the same duration the eyewash standard requires of the hardware. Get emergency medical care. No oils, ointments, or neutralizing drops.
2. Skin. Flood with water 15+ minutes while cutting off clothing, shoes, and leather (leather holds ammonia). Liquid-ammonia frostbite can hide under the chemical burn; keep flushing.
3. Inhalation. Move to fresh air. Sit the person upright if breathing is labored. Do not become a second victim. Seek medical evaluation even after a brief exposure in a rich cloud.
4. Never neutralize with acid. Water only.

That first-aid package is why the machinery room needs a working eyewash and shower, not a dusty squeeze bottle in a desk drawer. Hardware details are the next-next section; the chemical reason lives here.