R-717

Moderate — comparable to R-22 across most operating ranges. At 70°F R-717 saturation is approximately 114 PSIG (CoolProp 7.2.0); at typical industrial low-temperature evaporator setpoints (−20°F to −40°F), saturation runs 5-15 PSIG. Standard 500 PSI manifold gauges handle the operating envelope.

Operating pressures in industrial refrigeration: low-temperature evaporator 5-20 PSIG suction depending on setpoint; condenser 150-250 PSIG discharge depending on cooling water/air temperature.

Toxicity. Ammonia's NIOSH IDLH of 300 ppm and PEL of 25 ppm mean refrigerant releases pose acute personnel hazards. Industrial facilities can manage these risks through engineered controls (leak detection, ventilation, emergency response, designated machinery rooms with restricted access), trained personnel, and continuous monitoring — residential occupied spaces cannot.

For industrial scale, ammonia's thermodynamic performance (high latent heat, ~20% better cycle efficiency than HFCs in industrial applications) and zero environmental impact make it the preferred choice. For residential scale, the toxicity-management infrastructure isn't justifiable for the small refrigeration loads involved.

GWP 0 and ODP 0 — the best environmental profile of any commercial refrigerant alongside R-744 (CO₂) [ipccar5][ashrae34]. Ammonia is a naturally occurring compound; atmospheric breakdown via reaction with acids and rain-out is rapid (hours to days); no climate or ozone impact from refrigerant release.

The environmental excellence is why ammonia has held industrial refrigeration market share through 130+ years of changing refrigerant landscapes. Montreal Protocol (CFC/HCFC phase-out), Kigali Amendment (HFC phase-down), and other regulatory frameworks have not affected ammonia adoption.

Ammonia reacts with copper and zinc-bearing alloys (brass) to form copper-ammonia complexes that corrode the metal aggressively. The reaction is accelerated by moisture and is faster at higher temperatures. Industrial ammonia refrigeration uses carbon steel piping, fittings, and components exclusively [iiar2].

Service equipment for ammonia systems must also avoid copper/brass contact — special manifold gauges, hoses, and recovery cylinders are required. Mixing HFC service equipment with ammonia service equipment can introduce copper contamination that compromises ammonia system integrity.

Mineral oil typically, in industrial-grade viscosity specified by the equipment OEM (ISO 32, 46, or 68 depending on application). Some systems use synthetic alkylbenzene oils for specific compressor designs or operating temperature ranges.

POE and PAG oils (used with HFC refrigerants) are not used with ammonia — both have compatibility issues with NH₃ at typical operating temperatures and don't provide the lubrication characteristics ammonia systems require.

Mildly. The "2L" suffix in ammonia's B2L classification indicates mild flammability with low burning velocity. The lower flammability limit (LFL) is 15% by volume in air — substantially higher than hydrocarbon refrigerants like R-290 (LFL 2.1%). Concentrations between 15% and 28% by volume in air will ignite if exposed to sufficient ignition energy, but the high LFL means accidental ignition is far less likely than with A3 hydrocarbons.

The dominant safety concern for ammonia is toxicity (B classification) rather than flammability. Personnel exposure thresholds are far below the flammability concentration range — 300 ppm (IDLH, ~0.03% by volume) is dangerous to humans long before ammonia concentrations approach the 150,000 ppm (15%) flammability lower limit.

The International Institute of Ammonia Refrigeration (IIAR) is the trade association and standards-development organization for industrial ammonia refrigeration in North America [iiar]. IIAR publishes the IIAR Standard series (IIAR 1, 2, 3, 6, 7, 8, 9) covering equipment design, installation, operations, maintenance, and decommissioning of ammonia refrigeration systems [iiar2].

IIAR standards are referenced by EPA RMP guidance, OSHA PSM enforcement, and state-level building codes for ammonia refrigeration installations. Industrial ammonia refrigeration is structured around IIAR best practices; technicians and engineers in this specialty hold IIAR certifications.

Generally no. Ammonia refrigeration systems use carbon steel piping incompatible with HFC service; switching refrigerants would require complete pipework replacement. The economics rarely favor retrofit — ammonia equipment lasts 30-50 years with proper maintenance, and the environmental advantages of ammonia mean there's no regulatory pressure to change.

The opposite direction is more common: HFC industrial refrigeration retrofitting to R-744 CO₂ (transcritical or cascade) or to R-717 ammonia as part of HFC phase-down compliance. These conversions require full system replacement.