Building Code Glossary
Closed System: Building Code Definition
How the IBC 2009, IFC 2009 define closed system, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.
Direct answer
Closed system is a defined term in the International Building Code (IBC) 2009, in Use and Occupancy Classification. The code's own words are: “The use of a solid or liquid hazardous material involving a closed vessel or system that remains closed during normal operations where vapors emitted by the product are not liberated outside of the vessel or system and the product is not exposed to the atmosphere during normal operations; and all uses of compressed gases. Examples …” The IFC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 13 chapters of this corpus, most often in Flammable and Combustible Liquids (IFC 2009), Hazardous Materials-general Provisions (IFC 2009), Exhaust Systems (IMC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.
Content and cited inputs reviewed by Scott Barrington, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Closed System — IBC 2009, Use and Occupancy Classification:
The use of a solid or liquid hazardous material involving a closed vessel or system that remains closed during normal operations where vapors emitted by the product are not liberated outside of the vessel or system and the product is not exposed to the atmosphere during normal operations; and all uses of compressed gases. Examples of closed systems for solids and liquids include product conveyed through a piping system into a closed vessel, system or piece of equipment.
What must be verified before using this guidance?
Two of the I-Codes in this corpus define Closed System, in identical words.
| Code | Where it is defined | Definition |
|---|---|---|
| IBC 2009 | Use and Occupancy Classification | The use of a solid or liquid hazardous material involving a closed vessel or system that remains closed during normal operations where vapors emitted by the product are not liberated outside of the vessel or system and the product is not exposed to the atmosphere during normal operations; and all uses of compressed gases. Examples of closed systems for solids and liquids include product conveyed through a piping system into a closed vessel, system or piece of equipment. |
| IFC 2009 | Definitions | The use of a solid or liquid hazardous material involving a closed vessel or system that remains closed during normal operations where vapors emitted by the product are not liberated outside of the vessel or system and the product is not exposed to the atmosphere during normal operations; and all uses of compressed gases. Examples of closed systems for solids and liquids include product conveyed through a piping system into a closed vessel, system or piece of equipment. |
Where closed system is used in the code
The term appears in 13 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Flammable and Combustible Liquids | IFC 2009 | 13 |
| Hazardous Materials-general Provisions | IFC 2009 | 13 |
| Exhaust Systems | IMC 2009 | 13 |
| Semiconductor Fabrication Facilities | IFC 2009 | 12 |
| Use and Occupancy Classification | IBC 2009 | 4 |
| Definitions | IFC 2009 | 4 |
| Highly Toxic and Toxic Materials | IFC 2009 | 4 |
| Definitions | IMC 2009 | 4 |
| Refrigeration | IMC 2009 | 4 |
| Motor Fuel-dispensing Facilities and Repair Garages | IFC 2009 | 3 |
| Special Detailed Requirements Based on Use and Occupancy | IBC 2009 | 2 |
| Flammable Gases and Flammable Cryogenic Fluids | IFC 2009 | 2 |
1 further chapters mention the term.
The term in use
How the code actually writes about closed system, quoted from the 2009 text hosted here:
A report shall be submitted to the building official identifying the maximum expected quantities of hazardous materials to be stored, used in a closed system and used in an open system, and subdivided to separately address hazardous material classification categories based on Tables 307.1(1) and 307.1(2).
— IBC 2009, Special Detailed Requirements Based on Use and Occupancy
Closed System compared with Open System
These two are the closest pair in the 2009 I-Codes: about 58 per cent of their defining words are the same. The code states both and compares neither, so the difference is worth naming.
| Wording unique to it | |
|---|---|
| Closed System (IBC 2009) | closed, remains, emitted, outside, all, uses, compressed, gases, conveyed, through, piping, piece |
| Open System (IBC 2009) | continuously, open, dispensing, beakers, containers, dip, tank, plating |
Everything else in the two definitions is shared. If a project turns on which of the two applies, those words are the whole of the test — and a local amendment that edits one of them without editing the other moves the boundary between closed system and open system.
The terms closed system is built out of
The definition above leans on 5 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what closed system covers:
- Piping System — IRC 2009: All fuel piping, valves and fittings from the outlet of the point ofdeliveryto the outlets of the appliance shutoff valves.
- Equipment — IRC 2009: All piping, ducts, vents, control devices and other components of systems other than appliances that are permanently installed and integrated to provide control of environmental conditions for buildings.
- Exposed — IRC 2009: (As applied to live parts.) Capable of being inadvertently touched or approached nearer than a safe distance by a person.
- Liquid — IBC 2009: A material that has a melting point that is equal to or less than 68°F (20°C) and a boiling point that is greater than 68°F (20°C) at 14.7 pounds per square inch absolute (psia) (101 kPa).
- Piping — IRC 2009: Where used in this code, “piping” refers to either pipe or tubing, or both.
Closed System: what to open, and in what order
Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| Read the definition in the adopted IBC | Use and Occupancy Classification | |
| Read the definition in the adopted IFC | Definitions | |
| Re-check the requirement that uses it | Flammable and Combustible Liquids (IFC 2009) | |
| Re-check the requirement that uses it | Hazardous Materials-general Provisions (IFC 2009) | |
| Re-check the requirement that uses it | Exhaust Systems (IMC 2009) | |
| Re-check the requirement that uses it | Semiconductor Fabrication Facilities (IFC 2009) | |
| Confirm the dependent definition | Piping System | |
| Confirm the dependent definition | Equipment | |
| Confirm the dependent definition | Exposed | |
| Local amendment to any of the above | Jurisdiction's amendment list |
A research aid, not a code determination. The authority having jurisdiction decides which edition and which amendments apply.
Where can you explore related guidance?
- Explore all glossary guidance
- Piping System: Building Code Definition
- Equipment: Building Code Definition
- Exposed: Building Code Definition
- Vessel: Building Code Definition
Sources and method
Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The ICC code library publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of closed system?
The International Building Code (IBC) 2009 defines it in Use and Occupancy Classification as: “The use of a solid or liquid hazardous material involving a closed vessel or system that remains closed during normal operations where vapors emitted by the product are not liberated outside of the vessel or system and the product is not exposed to the atmosphere during normal operations; and all uses of compressed gases. Examples of closed systems for solids and liquids include product conveyed through a piping system into a closed vessel, system or piece of equipment.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.
Which parts of the code depend on closed system?
In this corpus the term is used across 13 chapters, led by Flammable and Combustible Liquids in the IFC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.
What does IBC mean in building codes?
Building is a separate defined term. The IBC 2009 defines it as: “Any structure used or intended for supporting or sheltering any use or occupancy.” That is not the same as closed system, which the IBC 2009 defines as “The use of a solid or liquid hazardous material involving a closed vessel or system that remains closed during normal operations where vapors emitted by the product are not liberated outside of the vessel or system and the product is …” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
What is a closed system in simple terms?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IBC 2009 states, in Use and Occupancy Classification: “The use of a solid or liquid hazardous material involving a closed vessel or system that remains closed during normal operations where vapors emitted by the product are not liberated outside of the vessel or system and the product is not exposed to the atmosphere during normal operations; and all uses of compressed gases. Examples …” It is defined in IBC 2009, IFC 2009. Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
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