By Priya Raman · Updated September 12, 2026 · 6 min read
Short answer
IIAR 2 is the American National Standard for the safe design of closed-circuit ammonia refrigeration systems, and IIAR 6 is the standard for inspection, testing and maintenance of those systems. They are published by the International Institute of Ammonia Refrigeration. Owners, engineers and contractors use them as recognized and generally accepted good engineering practice, and they support OSHA Process Safety Management mechanical integrity programs.
IIAR 2 and IIAR 6 are two standards from the International Institute of Ammonia Refrigeration. IIAR 2 covers the safe design of closed-circuit ammonia refrigeration systems. IIAR 6 covers how those systems are inspected, tested and maintained over their lives. Together they describe what a well-built and well-maintained ammonia system looks like, and they are widely used to show “recognized and generally accepted good engineering practice” under OSHA Process Safety Management.
This article is a general description. The standards themselves are copyrighted documents that you should obtain from IIAR, and editions are updated, so always work from the edition adopted in your jurisdiction.
What is IIAR 2?
IIAR 2 is titled as a standard for the design of closed-circuit ammonia refrigeration systems. It is an American National Standard, which means it was developed through a consensus process. In general terms it addresses:
- Design pressures and the rating of equipment, vessels and piping
- Pressure relief and venting arrangements
- Piping design, supports and materials suitable for ammonia
- Equipment room design, including ventilation and detection
- Controls, emergency shutdown and safety systems
- Valves, isolation and the ability to pump down or isolate sections
It is mainly used by design engineers, equipment manufacturers and installing contractors, and by owners who review designs. Many state and local codes and the International Mechanical Code and fire codes refer to it, though adoption varies by jurisdiction.
What is IIAR 6?
IIAR 6 covers inspection, testing and maintenance of closed-circuit ammonia refrigeration systems. It sets out the kinds of tasks that should be done, how often, and what records to keep. In general terms it covers:
- Scheduled inspections of equipment, piping, insulation and supports
- Testing of relief valves, safety controls, alarms and emergency systems
- Maintenance tasks for compressors, condensers, evaporators and pumps
- Recordkeeping so that results and corrective actions can be traced
It is used by operators, maintenance staff, contractors and auditors. Because it is organized around tasks and intervals, it translates directly into checklists and a computerized maintenance management system.
How do IIAR 2 and IIAR 6 compare?
| Aspect | IIAR 2 | IIAR 6 |
|---|---|---|
| Focus | Design | Inspection, testing and maintenance |
| When it matters most | New systems, modifications | Entire operating life |
| Main users | Engineers, manufacturers, installers | Operators, maintenance teams, auditors |
| Typical outputs | Design documents, drawings, calculations | Inspection records, test reports, work orders |
| Link to PSM | Process safety information, design basis | Mechanical integrity |
IIAR publishes other related documents too, for example on ventilation, minimum safety criteria and installation. Check the IIAR bookstore for the full list.
How do they relate to OSHA PSM and EPA RMP?
OSHA’s Process Safety Management standard and EPA’s Risk Management Program expect owners to follow “recognized and generally accepted good engineering practice.” For ammonia refrigeration, IIAR standards are commonly used as that benchmark.
- IIAR 2 helps a facility document the design basis and show that equipment is designed and installed to accepted practice. It supports the process safety information and pre-startup review elements.
- IIAR 6 helps a facility build the mechanical integrity program, with defined inspection and test tasks, intervals and records.
Following the standards is not the same as complying with the regulations. Each facility still has to meet every PSM and RMP element for itself. For the regulatory overview, see OSHA PSM and EPA RMP for ammonia facilities.
Who should know these standards?
- Facility owners and managers, because they are accountable for the program.
- Plant engineers and refrigeration operators, who run and maintain the system every day.
- Design engineers and installers, who apply IIAR 2 when building or changing a system.
- Auditors and insurers, who compare the facility’s practices with accepted standards.
If you are new to ammonia plants, start with ammonia refrigeration system basics and then read ammonia vs freon refrigeration for how the technology compares with synthetic refrigerants.
How should a facility use the standards in practice?
Standards only help if they turn into routines. A simple approach is to build a calendar from them.
- Assign ownership. One named person should be responsible for the ammonia system’s documents, inspection schedule and records.
- List recurring tasks. Inspections, testing of safety devices and relief valve replacement all have intervals. Put each interval on a shared calendar, with the date it was last done.
- Keep documents current. Piping and instrumentation diagrams, equipment lists and procedures should match what is actually installed. Changes should update the paperwork the same week.
- Train and record. Training for operators should be written down. Ask whether new staff understand the emergency procedures, not just whether they signed a form.
Compare your program against ammonia refrigeration system basics to confirm the equipment list is complete, and against ammonia R717 properties and safety basics so procedures reflect how the refrigerant actually behaves. Anything unclear should be taken to the standards text or to a qualified professional, because this summary is general education, not a compliance opinion.
Frequently asked questions
Are IIAR standards law?
On their own, they are voluntary consensus standards. They become binding when a code, regulation, permit or contract adopts them, and many jurisdictions and insurers refer to them. They are also commonly used as evidence of good engineering practice. Check which edition applies to you.
Does IIAR 6 replace a PSM mechanical integrity program?
No. IIAR 6 gives detailed tasks and intervals, but a facility still needs written procedures, trained personnel, documented deficiency correction and the other mechanical integrity elements that PSM requires.
Do older systems have to meet the latest IIAR 2?
Usually the standard applies to new systems and to modifications, but older systems should be reviewed, and PSM requires documenting that existing equipment is designed and maintained in line with recognized practice. A qualified engineer can advise how the current edition applies to a particular plant.
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