- Current IIAR references include IIAR 2-2021, IIAR 3-2022, IIAR 4-2020, IIAR 5-2025, IIAR 6-2025, IIAR 7-2025, IIAR 8-2020 and IIAR 9-2020 with Addendum A (2024).
- IIAR 2 provides the safe-design framework; IIAR 4 addresses installation and overpressure-protection relief piping.
- IIAR 3 covers ammonia refrigeration valves and strainers but explicitly excludes safety relief valves and compressor slide valves.
- Always check IIAR interpretations, addenda and errata together with the project edition and authority having jurisdiction.
››› Standards Scope
Use the IIAR suite as a system framework—not as one isolated PSV formula
IIAR standards address the full lifecycle of closed-circuit ammonia refrigeration systems. They cover system design, installation, startup, inspection and maintenance, operating procedures, decommissioning and minimum safety requirements for existing systems. Safety valves and relief piping therefore have to be reviewed as part of the complete refrigeration system rather than as standalone components.
The selected relief device still requires a defined overpressure scenario, required capacity, set pressure, ammonia phase, temperature, back pressure, materials, connection, discharge route and documented inspection basis. Other codes, regulations and project specifications may also apply.
Important standards limitation
This page summarizes how IIAR standards affect safety-valve and relief-system communication. Final design and compliance must be based on the official standards, current interpretations, addenda, errata, jurisdictional requirements and qualified engineering review.
››› IIAR Standards Map
Which IIAR standard applies at each system lifecycle stage?
Use the standards as a coordinated set. The most relevant document depends on whether the project concerns new design, installation, startup, mechanical integrity, operating procedures, decommissioning or an existing-system safety evaluation.
01
IIAR 1 — Definitions
Provides common terminology used throughout the IIAR standards so owners, engineers, contractors and authorities use consistent definitions.
02
IIAR 2 — Safe System Design
The central design standard for closed-circuit ammonia refrigeration systems, including equipment, piping, machinery rooms and overpressure-protection considerations.
03
IIAR 3 — Valves and Strainers
Covers materials, design parameters, marking, testing and documentation for ammonia refrigeration valves and strainers. It does not apply to safety relief valves.
04
IIAR 4 — Installation
Addresses installation of closed-circuit ammonia systems and overpressure-protection relief piping, including the installed arrangement surrounding the relief device.
05
IIAR 5 / 6 / 7 — Startup, ITM and Procedures
IIAR 5-2025 covers startup; IIAR 6-2025 covers inspection, testing and maintenance; IIAR 7-2025 covers operating procedures.
06
IIAR 8 / 9 — Decommissioning and Existing Systems
IIAR 8 addresses decommissioning. IIAR 9 establishes minimum safety requirements and an evaluation method for existing ammonia refrigeration systems.
››› Safety Valve Scope
Protect each ammonia pressure boundary against its maximum credible source
Ammonia refrigeration systems contain multiple pressure levels and operating states. High-pressure receivers, compressors, condensers, evaporators, low-pressure vessels, recirculators, liquid lines and isolated equipment sections may require different relief scenarios and valve arrangements.
Protected-boundary checklist
- High-pressure and low-pressure receivers
- Compressor discharge, oil separator and interstage equipment
- Condensers, evaporators and heat exchangers
- Recirculators, accumulators and surge drums
- Pumps, transfer lines and blocked-in liquid sections
- Vaporizers, pressure regulators and process ammonia skids
- Lowest-rated downstream piping and equipment
- Relief header, vent stack, diffusion tank or treatment system
››› Credible Ammonia Relief Cases
Define the overpressure event before sizing the relief device
A safety valve should not be selected from receiver size, pipe size or set pressure alone. The governing event must identify the maximum ammonia source, phase, temperature, required flow and discharge condition.
01
Compressor Blocked Discharge
Maximum compressor flow, discharge temperature, oil-separator pressure, recycle failure and downstream isolation may control required capacity.
02
Blocked Outlet or Isolation Error
Closed valves, plugged equipment or an incorrect operating lineup can remove the normal ammonia flow path and expose the protected boundary to a higher-pressure source.
03
Trapped Liquid Thermal Expansion
Liquid ammonia isolated between closed valves can develop high pressure as heat enters the line, pump section, evaporator circuit or transfer connection.
04
Heat Input and Fire Exposure
Heat entering a receiver, vessel or isolated equipment can generate vapor. Fire-case review depends on the applicable code and project requirements.
05
High Side to Low Side Failure
Regulator, control valve, heat-exchanger or internal component failure can expose lower-pressure equipment to a higher-pressure ammonia source.
06
Defrost, Liquid Carryover or Abnormal Operation
Hot-gas defrost, trapped condensate, liquid carryover, startup error or abnormal pressure shock may create a credible overpressure or unstable relief condition.
››› Capacity and Valve Selection
Required capacity must match ammonia phase, temperature and the governing source
The sizing basis should state whether the relieving fluid is ammonia vapor, liquid, flashing liquid or a two-phase mixture. Compressor displacement, heat input, failed control-device flow, trapped liquid volume or other source data should be documented for the governing case.
After the required load is established, verify the selected orifice and certified capacity, operating-pressure margin, seat construction, material compatibility, inlet loss, back pressure and installation arrangement. Do not assume that an ordinary gas valve is suitable for R717 service.
Sizing and selection inputs
- Protected equipment MAWP or design pressure
- Set pressure and allowable overpressure or accumulation
- Ammonia composition, phase and purity basis
- Operating and relieving temperature
- Required relieving load and calculation method
- Compressor capacity or failed-flow source data
- Selected orifice and certified valve capacity
- Operating-pressure margin and seat-tightness requirement
- Inlet pressure loss and outlet back pressure
- Applicable IIAR, equipment-code and jurisdictional requirements
››› Relief Discharge and Piping
Toxic ammonia discharge must be routed, supported and evaluated as part of the relief system
Relief discharge may be routed to an outdoor vent stack, common relief header, diffusion tank, scrubber, treatment system or another approved destination. The arrangement affects back pressure, capacity, personnel exposure, dispersion, drainage, inspection and maintenance.
01
Atmospheric Vent Stack
Review outlet location, height, direction, nearby air intakes, occupied areas, ignition sources, weather effects and maintenance access.
02
Common Relief Header
Evaluate simultaneous relief cases, header pressure, branch sizing, built-up back pressure and interaction between connected valves.
03
Diffusion Tank or Treatment System
Confirm the downstream system can accept the required ammonia load without excessive pressure or creating an uncontrolled release.
04
Back Pressure and Valve Type
Conventional, balanced bellows and pilot-operated designs respond differently to outlet pressure. Use manufacturer-certified limits and capacity corrections.
05
Dual Relief and Changeover Arrangement
Where multiple relief devices or changeover valves are used, verify that the required protection remains available during operation, testing and maintenance.
06
Drainage, Support and Reaction Force
Prevent liquid pockets, condensate and unsupported piping loads. Review discharge reaction force, thermal movement and mechanical stress on the valve.
››› Installation, Inspection and Records
IIAR 4, 5, 6 and 7 connect the relief design to installation and ongoing operation
A compliant calculation can be undermined by poor installation, blocked or damaged discharge piping, incorrect isolation, missing records or an inadequate inspection program. Startup, operating procedures and mechanical-integrity tasks should identify the relief devices and their associated piping as controlled safety equipment.
Lifecycle review checklist
- Correct valve tag, set pressure, orientation and flow direction
- Clean and adequately sized inlet piping
- Supported outlet piping and verified discharge destination
- Isolation and changeover arrangements under approved control
- Startup verification and removal of temporary restraints
- Inspection, testing and maintenance tasks and frequencies
- Operating procedures for normal, abnormal and emergency conditions
- Calibration, seat-tightness and pressure-test records
- Management of change for system or set-pressure modifications
- Current P&IDs, equipment data and relief-system documentation
››› Engineering Workflow
A practical IIAR ammonia relief-system review
Start with the applicable IIAR lifecycle stage and protected pressure boundary, then complete the scenario, sizing, discharge, installation and document review.
01
Confirm standards and jurisdiction
Identify the applicable IIAR editions, addenda, errata, interpretations, local code, owner specification and authority having jurisdiction.
02
Map the ammonia system
Identify high-side and low-side equipment, isolation points, pressure boundaries, compressors, regulators, pumps and relief discharge paths.
03
Define credible relief cases
Evaluate blocked discharge, isolation error, trapped liquid, heat input, high-to-low-side failure and abnormal operating cases.
04
Calculate required capacity
Use documented ammonia properties, source flow, pressure, temperature and phase for the governing scenario.
05
Select and verify the valve
Confirm valve type, set pressure, orifice, certified capacity, materials, seat and ammonia compatibility.
06
Review relief piping
Check inlet loss, common-header pressure, back pressure, safe discharge, support, drainage and changeover arrangement.
07
Plan startup and mechanical integrity
Define inspections, test reports, procedures, frequencies, records and management-of-change controls.
08
Complete the RFQ and dossier
Issue the datasheet, calculation basis, P&ID, drawings, certificates, test reports and final document index.
››› RFQ Data
Information needed for an IIAR ammonia refrigeration safety valve enquiry
A complete enquiry should identify the protected equipment, ammonia relief case and discharge system. A request containing only valve size and set pressure is not sufficient for sizing, material or documentation review.
Recommended engineering input
- Applicable IIAR standard editions and project code
- New design, modification, existing-system or replacement scope
- Protected equipment and refrigeration-system location
- MAWP or design pressure and set pressure
- Ammonia phase, purity basis and temperature
- Governing relief scenario and required capacity
- Compressor, regulator, pump or heat-input source data
- Inlet piping and outlet discharge arrangement
- Superimposed and built-up back pressure
- Valve materials, seat, connection and accessories
- Inspection, test and maintenance requirements
- Datasheet, calculation, certificates and document-index requirements
››› Related Applications and Standards
Continue the ammonia refrigeration pressure-protection review
The following links use current ZOBAI pages and connect IIAR system requirements with ammonia applications, sizing, discharge, installation and documentation.
01
Ammonia Safety Valves
Application guidance for R717 receivers, compressors, condensers, evaporators, pumps, storage and process skids.
02
Compressor Safety Valves
Blocked discharge, oil separators, interstage equipment, vibration, pulsation and hot ammonia gas.
03
Pressure Vessel Safety Valves
Receivers, accumulators, recirculators and ammonia pressure vessels requiring documented relief capacity.
04
Back Pressure and Bellows
Review common relief headers, outlet pressure, balanced bellows and valve-type limitations.
05
API 520 Safety Valve Sizing
Sizing and selection reference where the project specifies API-style pressure-relief calculations or certified capacity.
06
Safety Valve Certificates
Material, type-test, calibration, pressure-test, seat-tightness and project-document review.
››› FAQ
Common questions about IIAR ammonia refrigeration standards
IIAR 2 is the central safe-design standard for closed-circuit ammonia refrigeration systems. IIAR 4 is particularly relevant to installation and overpressure-protection relief piping. The applicable project may also require other codes and jurisdictional rules.
No. IIAR 3 covers ammonia refrigeration valves and strainers but explicitly excludes safety relief valves and compressor slide valves. Safety relief devices must be selected and documented under the applicable relief-device, equipment and project requirements.
IIAR 5-2025 addresses startup. IIAR 6-2025 addresses inspection, testing and maintenance. IIAR 7-2025 addresses operating procedures for closed-circuit ammonia refrigeration systems.
IIAR 9 establishes minimum system safety requirements and an evaluation method for existing closed-circuit ammonia refrigeration systems. Addendum A (2024), current interpretations and associated evaluation tools should be checked where applicable.
Provide the protected equipment, MAWP, set pressure, ammonia phase, temperature, governing relief case, required capacity, source-flow data, inlet loss, back pressure, discharge destination, materials and required documents.
The discharge should go to an approved safe destination such as a properly designed outdoor vent, common header, diffusion tank, scrubber or treatment system. Toxic exposure, back pressure, dispersion, occupied areas and maintenance access must be reviewed.
Need an ammonia relief-system review for an IIAR project?
Send the P&ID, equipment data, IIAR edition, relief scenarios, required capacity, discharge-system information and document requirements. ZOBAI can identify missing inputs and define the next sizing, selection or quotation step.