2.1 IIAR 2 and ASHRAE 15 Machinery-Room Design

Who Writes the Design Rules?

Quick Answer: For a U.S. closed-circuit ammonia plant, ANSI/IIAR 2-2021 is the ammonia-specific safe-design standard. ASHRAE 15 remains the general refrigeration safety standard. Model codes such as the International Mechanical Code (IMC) and International Fire Code (IFC) send ammonia systems to the IIAR suite instead of treating ammonia as just another ASHRAE 15 refrigerant.

The International Institute of Ammonia Refrigeration (IIAR)—now branded the International Institute of All-Natural Refrigeration—is an ANSI-accredited standards developer. That accreditation matters on the CIRO exam: IIAR documents are not vendor pamphlets. They are consensus American National Standards written in enforceable code language. When a question asks which body writes ammonia refrigeration design rules, the answer is IIAR, not ASHRAE, OSHA, or the local fire marshal acting alone.

ASHRAE 15, Safety Standard for Refrigeration Systems, is the general mechanical-refrigeration safety standard. It covers occupancy classifications, refrigerant safety groups, machinery rooms, pressure relief, and related safeguards for refrigerating systems as a class. Ammonia (R-717) still appears in that general framework, but IIAR 2 supplies the ammonia-specific design detail that industrial engine rooms actually get built from: detector counts and setpoints, ammonia emergency ventilation, ammonia-compatible materials, and ammonia machinery-room construction.

Think of the split this way. ASHRAE 15 answers, “What does a safe refrigerating system look like in general?” IIAR 2 answers, “What does a safe closed-circuit ammonia system look like?” A CIRO supervisor who quotes only ASHRAE 15 on an ammonia machinery-room detector question is answering the wrong standard.

How model codes point to IIAR

U.S. model codes used to write overlapping ammonia rules. That overlap has been shrinking. The 2021 IMC states that refrigeration systems using ammonia shall comply with IIAR 2, IIAR 3, IIAR 4, and IIAR 5 and shall not be required to comply with IMC Chapter 11. Earlier IFC language already sent ammonia design and installation to IIAR 2 and operating procedures to IIAR 7. Later code cycles continue that pattern by listing additional IIAR standards (including inspection, operating procedures, decommissioning, and existing-system minimums). You do not need to memorize every code-cycle table. You do need this exam idea: the adopted mechanical and fire codes are the legal hook; the IIAR suite is the ammonia technical content.

The authority having jurisdiction (AHJ)—building official, fire official, or both—still has the last word on the adopted edition. A plant in a 2015-code city is not automatically on 2021 IMC language. The supervisor’s job is to know which standard answers the technical question, then confirm the adopted edition with the AHJ and the plant’s RAGAGEP file.

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ANSI/IIAR 2-2021 Machinery Rooms

ANSI/IIAR 2-2021, Standard for Safe Design of Closed-Circuit Ammonia Refrigeration Systems, is the current design standard. IIAR 2 is under review for a targeted 2026 revision; until that revision is ANSI-approved, IIAR 2-2021 is the design edition to teach and apply. It is not the inspection standard (that is IIAR 6), not the procedure-writing standard (IIAR 7), and not the existing-system minimum-safety standard (IIAR 9).

Chapter 6 of IIAR 2 is the machinery-room chapter. A machinery room is not “the room with the screws in it.” It is a designed occupancy: a room built so that high-probability ammonia equipment can be isolated, ventilated, detected, drained, lighted, and shut down without turning the rest of the plant into a spray chamber.

Construction, access, storage, drainage, and lighting

IIAR 2 machinery-room design addresses, among other things:

• Construction and fire protection of the room, including how the room is separated from other occupancies.
• Access and egress. Doors must support escape and responder entry. The designated principal machinery-room door is the reference point for emergency control switches.
• No combustible storage as ordinary engine-room clutter. Compressor oil drums and rags are a classic finding. Oil products belong in a fire-rated storage container or outside the machinery room. Combustible storage is not a housekeeping preference; it is a design and occupancy violation.
• Drainage so leaked ammonia, oil, and fire-suppression water have a designed path instead of pooling around starters.
• Lighting so operators can read valves, nameplates, and emergency devices. If the lights fail during a release, the emergency plan is already behind.
• Open flames, hot surfaces, and fuel-burning appliances are restricted. Fuel-fired equipment does not belong in an ammonia machinery room unless the standard’s narrow exceptions (for example, combustion air ducted from outside) are met.
• Eyewash and safety shower provisions for the machinery room, coordinated with the plant’s ANSI Z358.1 program (taught in the ammonia-hazards chapter).

A CIRO walking an engine room should be able to narrate those features without opening the book. If pallets of cardboard, a gasoline-powered welder, or a domestic water heater share the compressor floor, the room is not meeting the design intent of IIAR 2.

Emergency control switches

IIAR 2 requires clearly identified emergency controls outside and adjacent to the designated principal machinery-room door:

1. Emergency shutdown (e-stop) for refrigeration equipment. The switch provides off-only control of refrigerant compressors, refrigerant pumps, and normally closed automatic refrigerant valves in the machinery room. It is clearly marked, readily operable, protected from accidental bumping, and requires manual reset. It does not kill every electrical load in the room. Emergency ventilation must keep running. An air compressor, lighting panel, or non-refrigeration motor that stays live after the refrigeration e-stop is not a “pass” if the question is about shutting down refrigerant machinery—and it is a serious ignition and confusion problem if operators believe they de-energized the entire room.
2. Emergency ventilation control switch. For emergency ventilation that is not already running continuously at the emergency rate, a clearly identified switch provides ON/AUTO override. ON forces emergency ventilation. AUTO returns control to the detection system. The function is marked by signage at the controls. This switch is the device a responder uses without entering a 200 ppm room.

If a contractor mounts those switches inside the room “so they don’t get hit by forklifts,” the design failed. If the plates say only “FAN” and “STOP,” the design failed. CIRO-level supervision includes verifying the location, labeling, and function, not just that two red boxes exist.

Detection: the numbers the exam will use

ANSI/IIAR 2-2021 machinery-room detection is a ladder, not a single horn. Machinery rooms shall have at least two detectors with identical sensing ranges, plus audible and visual alarms inside the room and outside each entrance.

Three exam traps sit in that table. First, 25 ppm is not emergency ventilation. It is monitored-location notification and local warning. Second, 150 ppm ventilation is latched. A supervisor who “waits for it to clear and lets the fan stop by itself” is describing the 25 ppm alarm, not the 150 ppm emergency mode. Third, the high-concentration shutdown is refrigerant rotating equipment, not a promise that every motor in the room is dead. Emergency ventilation stays up.

“Level 1” in IIAR 2 is the 25 ppm monitored-location package used especially for areas other than machinery rooms. Machinery rooms are more demanding than a single Level 1 detector: two matched-range detectors, entrance horns/strobes, the 150 ppm ventilation latch, and the high-concentration compressor/pump trip. Do not tell an examiner that an engine room needs “only one 25 ppm detector.”

Ventilation that matches the detectors

Emergency ventilation is useless if the fan cannot start, the makeup path is blocked, or the exhaust dumps into a dock door. IIAR 2-2021 machinery-room ventilation design, as applied in industry summaries of the standard, includes these supervisor-level facts:

• Exhaust to the outdoors, not less than 20 ft from a property line or from building openings, measured so the plume does not re-enter occupied space.
• Emergency rate: 30 air changes per hour based on gross machinery-room volume (the IMC also cites 30 ACH for ammonia emergency ventilation by reference to IIAR 2). Reduced emergency airflow requires supporting engineering analysis, not a verbal “we never needed that much.”
• Makeup air must replace exhaust so the room does not pull doors shut. Negative pressure relative to adjacent spaces is limited (0.25 in. water column is the widely cited IIAR 2 limit).
• Emergency exhaust motors in the airstream or inside the room are totally enclosed; they need not be explosion-proof. Blades are non-sparking (two ferrous parts must not strike).
• Motorized makeup dampers fail open on loss of power.
• Emergency ventilation is powered independently of the refrigeration e-stop. Proving airflow (sail switch, current switch, or differential) is part of the design, not a nice-to-have.
• Non-emergency fans are de-energized at 150 ppm unless they are part of the emergency system.

Occupied/normal ventilation (temperature control, the greater of a floor-area rate or a per-person rate) is a design calculation. The CIRO exam cares more that you can distinguish normal ventilation from latched emergency ventilation at 150 ppm.

Equipment that is not in a machinery room

IIAR 2 does not require every pound of ammonia to live behind an engine-room door. Chapter 7 covers equipment in areas other than machinery rooms. IIAR 2 and the IIAR 9 existing-system list (which restates the same equipment families) permit, in industrial occupancies, items such as:

• Evaporators used for refrigeration or dehumidification (the penthouse coil, the blast-cell evaporator).
• Condensers used for heating the space in which they are located (not “any condenser anywhere”).
• Low-probability pumps.
• Valves and connecting piping associated with those allowed items.
• An ammonia system, or portions of one, with total connected compressor drive power not exceeding 100 HP (74.6 kW) in the listed cases.

Compressors and open-drive pumps belong in a machinery room or outdoor machinery area unless that small-connected-drive exception applies. A 400 HP screw on a production-floor mezzanine is not “basically an evaporator.” Outdoor equipment is allowed when sited to IIAR 2 (including the 20 ft opening/property-line relationship, with listed packaged-system exceptions). Listed equipment with a very small charge (IIAR 2 cites not more than 6.6 lb / 3 kg of ammonia) may be installed without a machinery room when installed to the listing.

Detection outside machinery rooms is generally the Level 1 package (at least one detector, 25 ppm to a monitored location), with additional rules where emergency ventilation is required. Unoccupied areas of continuous welded pipe with no valves or equipment may not need detection. AHJ-allowed exceptions exist for continuously occupied, regularly patrolled rooms and for harsh environments incompatible with sensors. Those exceptions are not a supervisor’s verbal waiver.

Supervisor call: adding a vessel versus walking an old engine room

A cold-storage plant wants a new high-pressure receiver in the existing engine room. That is new design. The vessel, its relief, detection interactions, ventilation capacity, and emergency-switch coverage are IIAR 2 (plus IIAR 4 installation and IIAR 5 startup). You do not “IIAR 9 the new receiver” because the building is old.

The same afternoon, the night operator reports that only one detector is in alarm and the entrance strobe is dead. That is an existing-room problem: restore the two-detector, matched-range, entrance A/V design function, and treat 150 ppm as a latched emergency-ventilation event—not a “wait and see” 25 ppm warning. If the plant’s original code was weaker than IIAR 2-2021, IIAR 9 may set the minimum for the existing installation, but it does not authorize installing a new vessel to 1980s detection logic.

On the exam, pick the standard that matches the work: IIAR 2 for how a machinery room and new ammonia equipment shall be designed; ASHRAE 15 for general refrigeration safety context; the adopted IMC/IFC for the legal pointer; IIAR 6 for whether the detectors and fans still work.