IIAR 2 – 2021 Standard for Design of Safe Closed-Circuit Ammonia Refrigeration Systems has been released by the IIAR and is now available for purchase on their website

The updated standard has several new requirements which resulted in some changes in the PSM/RMP program templates. Here are some of the highlights:

  1. The definitions file was updated with new IIAR 2 definitions. Added in-document headings to skip around the document easily.
  2. The PHA Checklist Template was updated to the new IIAR 2:
    • Added a note that “Provisions for plugs or caps required under IIAR 2” on all oil draining plug/cap questions.
    • Added a note that “IIAR 2-2021 5.12.2 requires a check valve during charging” in relevant Charging SOP section.
    • Added a question on Provisions for Pumpout per IIAR 2-2021 5.12.6 on PV1 subsection and all Equipment Subsections.
    • Added/Modified questions on RC1 section about low ambient temperature, and VFD resonance.
    • Added a question on EV2 (Liquid Heat Exchanger) equipment subsection regarding secondary coolant side pressure ratings.
    • Added a question on MR.C Checklist for Classified Space signage.
    • Added a question on PV1 (Piping & Valves) on new MOPD & MSSPD requirements for valves leading to atmosphere.
    • Added a question on PV1 (Piping & Valves) on requirements for unique identification for Emergency Shutoff valves.
    • Modified existing .PSV equipment sub-subsections to include IIAR 2 2021 15.2.6 requirement that liquid relieving reliefs relieve back into the system.
    • Added a note that IIAR 2 2021 limits carbon steel tubing and carbon steel compression fittings to valve sensing pilots, compressors, compressor packages, and packaged systems to all small-bore piping / tubing questions.
    • Updated MR.C section for new requirements regarding NH3 detection.
    • Updated various checklists (VENT, DET, PSV, DT) to match current IIAR 2-2021 text.
    • Added a new equipment subsection NMR.C for IIAR 2 Equipment located outside of Machinery rooms.
    • Added a new equipment subsection PKG.C for IIAR 2 Packaged Systems and Equipment.
    • Added a new equipment subsection IAC.C for IIAR 2 Instrumentation Controls.
  3. Updated “Contractor Door Sign” to meet new IIAR 2 – 2021 [] information standards and some ASHRAE 15 – 2019 [11.2.1] standards.

Comments about the changes and the required steps to implement the document changes are present in the “Change Log and Reference” document at 08/02/21.

…Read on further in this post if you want to know about the changes in the new IIAR 2…


For a rapid fire synopsis of SOME changes in IIAR 2-2021 that you may want to investigate:

  1. The definition of surge drums, what they are, and where they are allowed to be located within the plant was made official from a previous letter of interpretation.
  2. The language surrounding pipe and vessel design pressures was modified. Verify your future projects take this into account.
  3. The requirements surrounding manual purge point terminations was loosened.
  4. More overt verbiage was added to require lines terminating to atmosphere to be plugged/capped when not in use for maintenance/service. This was already best practice and referenced in other standards, but it is now firmly stated in the design standard.
  5. There is modified verbiage requiring additional justification for equipment/pipe support. Again, ensure that future work is documented properly in order to satisfy this standard.
  6. There is now a hard requirement that charging operations take place with a check valve in place. This was already a feature in most every installation, but attention should be given to infrequent charging operations if they happen elsewhere in the system.
  7. Emergency shutdown valves are now required to be accessible even when response PPE is donned. If you have several key valves involved in an emergency shutdown of your facility, look to see whether someone wearing an SCBA and suit during a response can access them. This is not a retroactive requirement, but still something to look at with regards to emergency action plans and PHA questions.
  8. The requirements to be notified during a failure (or partial failure) of mechanical ventilation have changed. Again this is not applicable to existing facilities, but this is the direction the industry is moving and it may help you analyze your current safeguards/notification system.
  9. The IIAR has expressly copied verbiage from ANSI Z358.1 into the standard. This standard has existed for over 30 years, applies to virtually every refrigerant (not just ammonia), but will still come as a shock to some.
  10. Some fittings have more formal restrictions added to ensure unsound materials and construction practices don’t find their way into our systems.
  11. Valves terminating to the atmosphere have a new requirement added to ensure they do can handle the differential pressures between the system and the atmosphere once a plug/cap is removed. This shouldn’t be a big change for most, as the valves this portion of the standard protects against were always a terrible idea for ammonia systems.
  12. The relief calculation factor regarding nearby flammables now expressly excludes the materials the building is made out of. This was always the intent of the old language, but this version adds clarity to that.
  13. Oil pots no longer have an exception for the placement of atmospheric pressure relief valves. All valves relieving vapor are now to be above the liquid level, period. Additionally, all valves that relieve liquid are to go back into the system. These changes remove some of the grey area that engineers have squabbled over in years past.
  14. Ammonia detectors are now required to be “designed and tested in accordance with UL-61010-1 “Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use” or ANSI/ISA 92.00.01 “Performance requirements for Toxic Gas Detectors”. At the time of writing we have received mixed reports from several major manufacturers as to whether or not they meet either of these standards. There is at least one that is assuredly compliant. Look into your ammonia detectors to see if they meet this requirement. At a minimum, review any new, changed, or repaired detectors against this standard.
  15. Ammonia detection in the machinery room is now required to have redundant ammonia detectors unless very specific interlocks are in place. This will be a change to many companies and contractors who design and install detection systems. The interlocks are not overly complex, but they don’t make their way naturally into most new installs, so changes to planning may be required.

The list above is not exhaustive  – there are many other changes that occurred in this updated standard. If you want to know more or have a major project coming up that will need to be adherent to this standard, please read it through in depth for yourself.

Please feel free to reach out for clarification on any of these points or if you need anything else in the realm of process safety.

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