What Really Happens During an Ammonia Release?

Understanding how ammonia behaves when it is accidentally released is extremely important for protecting people, facilities, and the environment. When stored under pressure, ammonia can rapidly turn into a mixture of gas and cold liquid droplets known as a two-phase release, that creates visibility hazards, breathing risks, and unpredictable movement through indoor spaces.

The following information is a simplified technical summary of the 186-page Jack Rabbit III laboratory study conducted by the U.S. Department of Homeland Security. In this study, researchers released small amounts of pressurized ammonia inside a controlled test chamber so that temperature, humidity, and other environmental conditions could be adjusted and studied. By monitoring gas concentrations, liquid pooling, cloud visibility, and residue formation, the research provides valuable insight into how real-world ammonia leaks behave and how quickly they disperse.

Ammonia is widely used in agriculture, refrigeration, energy systems, and industrial manufacturing. Although it offers strong thermodynamic properties and a favorable carbon profile, ammonia presents critical hazards if accidentally released, especially in pressurized systems. The Jack Rabbit III (JR III) study findings were released in March 2025 and was executed to close longstanding knowledge gaps regarding ammonia dispersion, chemical behavior, and exposure potential during accidental releases. This project simulated pressurized two-phase ammonia releases inside a controlled, sealed chamber and systematically varied temperature, humidity, rain, and CO₂ levels. High-resolution instrumentation, high-speed digital video, and infrared imaging were used to track vapor behavior, liquid accumulation, and solid formation. This combined summary consolidates the technical setup, environmental conditions, results, and practical implications for industry and emergency response.

1. Why the Research Was Conducted

Historically, ammonia release studies have been conducted outdoors, which makes results dependent on wind, sunlight, air exchange, and unpredictable weather. JR III provided a uniquely controlled system, a sealed chamber where every environmental variable could be adjusted and held constant. The study supports major industry priorities:

• More accurate hazard-zone modeling for ammonia releases

• Better understanding of indoor ammonia gas buildup

• Improved ventilation and scrubbing strategies

• More confident mass-balance predictions

• Safer emergency entry procedures after a release

• Data to improve predictive software used by industry and regulators

  
  

Because ammonia is now also being evaluated as a low-carbon energy carrier, this research directly supports emerging national risk-assessment needs.

2. Test Chamber and Environmental Conditioning

A carbon-steel chamber was engineered to simulate a sealed industrial space. The usable test volume was reduced to approximately 51 m³ by constructing an insulated internal wall, shortening the conditioning time.

Chamber Characteristics

| Feature | Details ||—|—|| Height | ~9.5 ft (2.9 m) || Width | ~9.5 ft (2.9 m) || Length | 20 ft (6.1 m) || Thermal insulation | 3-in closed-cell spray foam || Wall protection | Alkyd enamel coating + HDPE liners |

The chamber could be conditioned to:

• Temperatures: −15°C to 40°C (5°F to 104°F)

• Relative humidity (RH): 10% to 90%

  
  

Fans were intentionally kept off during most of the experiment to allow natural dispersion; they were activated after 30 minutes to homogenize concentrations.

Ammonia release study, room layout.

3. Ammonia Release Method

Source Bottle Details:

• 12-in (30.5 cm) lecture bottle

• Filled with 153 g–199 g of liquefied ammonia

• Mounted at a 45° downward angle above a catch tray

• Released through a full-bore flow path

  
  

A pneumatic remote-release valve was used, rated for:

• 720 psig design conditions

• cryogenic temperatures of −46°C / −50.8°F

  
  

A redundant safety valve remained offline unless needed.

The average release duration was 10 seconds, which produced a rapid flash into cold liquid droplets and gas‐phase ammonia. Approximately 0.34 to 0.44 pounds of ammonia were released during each test scenario.

Ammonia release study.

4. Instrumentation Used to Characterize Release Behavior

Multiple sensor types and cameras collected simultaneous real-time data:

Gas Concentration – PIDs

MiniPID2 sensors were deployed at 18 sensor heights at multiple distances.

Characteristics:

• Response < 8 seconds

• Operational range: −40°C to 65°C

• Humidity tolerance up to 90%

• Calibration before every test

• Conversion factor: 10 mV ≈ 85 ppm

  
  

  

  Ammonia release study, sensor placement.

  
  
  
  

These sensors captured strong concentration gradients, especially during the first 1–5 minutes.

Temperature – Thermocouples

Two probe types were used:

1. Stainless-steel sheathed probes

Used for:

• Ammonia vapor temperature

• Liquid pooling temperature

  
  

2. Exposed-tip probes

Used on walls and external metal surfaces.

Notable readings:

• Pooling liquid commonly measured near −60°C / −76°F

• Chamber and plume temperatures changed rapidly during jet momentum dissipation

  
  

Pressure Measurements

Three pressure transducers recorded:

• Lecture bottle pressure drop

• Ambient chamber pressure

• Rain system injection pressure

  
  

Bottle pressure decayed from vapor-pressure equilibrium to ambient during ~10 seconds.

Liquid Mass Measurement

A weighed aluminum tray recorded:

1. Rained-out liquid ammonia

2. Evaporation loss

3. Post-test residue

   
   

Resolution capability: 0.2 grams Real-time mass data provided evaporation curves.

Video and IR Imaging

HD Cameras Captured:

• plume geometry,

• opacity thickness,

• liquid motion patterns.

  
  

FLIR IR Cameras Captured:

• relative temperature distributions,

• cooling effect from flash vaporization,

• droplet settling patterns.

  
  

Example imagery showed clear boundary layers:

• Cold plume edges surrounded by warmer air

• Hot environmental tests yielding minimal liquid footprint

  
  

  

  Infrared images of an ammonia release.

  
  

5. Behavior During the First Few Minutes After Release

Immediately after discharge:

Jet Impact Behavior

• The ammonia jet struck the catch tray, splashing outward

• Liquid droplets reflected upward

• Vapor shot toward the ceiling

• Strong eddies circulated gas across walls and corner boundaries

  
  

This caused extreme variation in concentrations at different heights:

• Lower sensors initially measured up to −4000 ppm lower than upper sensors

• Then reversed to appear 2000–6000 ppm higher

  
  

This inversion occurred because:

1. Large plume bounced upward immediately

2. Then evaporated liquid in the tray raised concentrations near the floor

   
   

It took 10–30 minutes before concentrations converged.

| Short-term initial spike | Up to 6,000 ppm |

| Average concentration after full mixing | 4,300–4,700 ppm |

6. Effects of Environmental Variables

A. Temperature Effects

Temperature was the most dominant factor.

Cold Condition Outcomes (−15°C / 5°F)

• Higher liquid yield

• Larger droplet sizes

• More persistent cloud

• Slower vapor-phase mixing

• Solid residue formation was observed

  
  

Warm Condition Outcomes (35–40°C / 95°F–104°F)

• Flashing led to more immediate vaporization

• Less liquid captured in tray

• Faster concentration equalization

• Fewer solids produced

  
  

B. Humidity Effects

Humidity directly impacted visibility.

High Humidity (~90%)

• Cloud was thick, white, persistent

• Likely composed of:

  • condensed water vapor

  • entrained ammonia droplets

• LC visibility lingered longer near surfaces

  
  

Low Humidity (10–25%)

• Minimal visible cloud

• Most ammonia transitioned to gas immediately

• Mixing rate was faster

  
  

Cloud visibility was NOT controlled primarily by ammonia quantity—rather, by water vapor condensation.

C. Rain Effects

A controlled rain nozzle discharged droplets during selected tests.

Observed outcomes:

• Rainwater actively dissolved ammonia

• Mid-field concentrations significantly reduced

• Rainout improved gas scavenging from air

• Collected water exhibited elevated pH (alkaline)

This confirmed a real-world mitigation principle:

"Rain significantly lowers downwind ammonia exposure levels."

D. CO₂ Interaction Effects

CO₂ did not directly react with ammonia gas upon release, but when moisture was present, carbonic acid formed and reacted with ammonia.

Results:

• Solids formed at locations where liquid remained pooled

• Residues had measurable pH between 7 and 10

• Post-test solids often resembled crystalline powder

  
  

Chemical products included:

• Ammonium carbonate

• Ammonium bicarbonate

• Possible ammonium carbamate under cold, low-humidity conditions

  
  

CO₂ greatly increased solid persistence time.

7. Solid and Liquid Residue Observations

Residues varied between test conditions.

| Condition | Observation | Cold, dry | Fragile white solids that sublimed rapidly || Warm, humid | Almost no solid formation || CO₂ present | Thick, stable solid deposits remained |

Solid sublimation was documented up to 150 minutes post-release.

Residue location distribution:

• Mostly on tray edges

• Around base walls

• At splash locations where droplets accumulated

  
  

8. Practical Real-World Implications

For Industrial Facilities:

• A short-duration high-pressure release can lead to prolonged concentration buildup indoors

• Pools of liquid ammonia may remain cold enough to continue releasing vapor long after primary event

• Fan activation timing affects exposure and spread

  
  

For Hazard Analysts:

• Initial concentration gradients do not follow textbook plume assumptions

• Physical splashing alters deposition zones

• Indoor mixing times may exceed 30 minutes

  
  

For Responders:

• A visible cloud does NOT always indicate high ammonia concentration

• Rain or water spray may be an effective mitigation strategy

• Delayed entry protocols should consider sustained volatilization from cold pooling

  
  

For Model Developers:

• Data supports high-resolution dispersion algorithms

• Aerosol phase must be included

• CO₂–humidity–temperature chemistry must be represented

  
  

Conclusion

The JR III controlled chamber study represents the most detailed technical evaluation of pressurized ammonia behavior in an enclosed environment to date. The findings establish that ammonia’s post-release trajectory depends heavily on environmental conditions:

• Cold environments prolong liquid phase

• High humidity increases cloud visibility

• Rain rapidly reduces airborne concentration

• CO₂ promotes solid residue formation

  
  

Understanding these interactions is critical to improving:

• ammonia storage safety,

• engineering system design,

• emergency response protocols, and

• consequence modeling accuracy.

  
  

This research provides foundational experimental data that the ammonia industry, safety regulators, academia, and emergency response organizations can use to minimize risk and protect personnel, facilities, and surrounding communities.

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