Updated 2026-09-07

Building Code Glossary

Flammable Liquids: Building Code Definition

How the IMC 2009 define flammable liquids, where the wording differs, and which chapters depend on the term.

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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.

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Direct answer

Flammable liquids is a defined term in the International Mechanical Code (IMC) 2009, in Definitions. The code's own words are: “Any liquid that has a flash point below 100°F (38°C), and has a vapor pressure not exceeding 40 psia (276 kPa) at 100°F (38°C). Flammable liquids shall be known as Class I liquids and shall be divided into the following classifications:” No other I-Code in this corpus defines it, so the IMC 2009 definition is the one to work from. The term is used in 17 chapters of this corpus, most often in Flammable and Combustible Liquids (IFC 2009), Explosives and Fireworks (IFC 2009), Special Detailed Requirements Based on Use and Occupancy (IBC 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?

Flammable Liquids — IMC 2009, Definitions:

Any liquid that has a flash point below 100°F (38°C), and has a vapor pressure not exceeding 40 psia (276 kPa) at 100°F (38°C). Flammable liquids shall be known as Class I liquids and shall be divided into the following classifications:

Labeled code-term definition diagram: Flammable Liquids: Building Code Definition — How the IMC 2009 define flammable liquids, where the wording differs, and which chapters depend on the term.

What must be verified before using this guidance?

Flammable Liquids is defined once in this corpus, in the Definitions chapter of the International Mechanical Code (IMC) 2009:

Any liquid that has a flash point below 100°F (38°C), and has a vapor pressure not exceeding 40 psia (276 kPa) at 100°F (38°C). Flammable liquids shall be known as Class I liquids and shall be divided into the following classifications:

Where flammable liquids is used in the code

The term appears in 17 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	34
Explosives and Fireworks	IFC 2009	11
Special Detailed Requirements Based on Use and Occupancy	IBC 2009	9
Motor Fuel-dispensing Facilities and Repair Garages	IFC 2009	5
Semiconductor Fabrication Facilities	IFC 2009	5
Aviation Facilities	IFC 2009	4
Water-reactive Solids and Liquids	IFC 2009	3
Fire Protection Systems	IBC 2009	2
Use and Occupancy Classification	IBC 2009	2
Lumber Yards and Woodworking Facilities	IFC 2009	2
Manufacture of Organic Coatings	IFC 2009	2
Pyrophoric Materials	IFC 2009	2

5 further chapters mention the term.

The term in use

How the code actually writes about flammable liquids, quoted from the 2009 text hosted here:

The applicable requirements of Chapter 27, other chapters of this code, the International BUilding Code and the International Mechanical Code pertaining to flammable liquids shall apply.

— IFC 2009 §3401.3

Delivery of flammable liquids to tanks more than 1,000 gallons (3785 L) in capacity shall be made by means of approved liquid- and vapor-tight connections between the delivery hose and tank fill pipe.

— IFC 2009 §2205.1.3

Electrical equipment and devices within 5 feet (1524 mm) of workstations in which flammable or pyrophoric gases or flammable liquids are used shall comply with NFPA 70 for Class I, Division 2 hazardous locations.

— IFC 2009 §1803.7.2

The terms flammable liquids is built out of

The definition above leans on 4 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what flammable liquids covers:

Vapor Pressure — IFC 2009: The pressure exerted by a volatile fluid as determined in accordance with ASTM D 323.
Flash Point — IBC 2009: The minimum temperature in degrees Fahrenheit at which a liquid will give off sufficient vapors to form an ignitable mixture with air near the surface or in the container, but will not sustain combustion.
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).
Shall — IRC 2009: The term, when used in the code, is construed as mandatory.

Flammable Liquids: 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 IMC	Definitions
Re-check the requirement that uses it	Flammable and Combustible Liquids (IFC 2009)
Re-check the requirement that uses it	Explosives and Fireworks (IFC 2009)
Re-check the requirement that uses it	Special Detailed Requirements Based on Use and Occupancy (IBC 2009)
Re-check the requirement that uses it	Motor Fuel-dispensing Facilities and Repair Garages (IFC 2009)
Confirm the dependent definition	Vapor Pressure
Confirm the dependent definition	Flash Point
Confirm the dependent definition	Liquid
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.

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 flammable liquids?

The International Mechanical Code (IMC) 2009 defines it in Definitions as: “Any liquid that has a flash point below 100°F (38°C), and has a vapor pressure not exceeding 40 psia (276 kPa) at 100°F (38°C). Flammable liquids shall be known as Class I liquids and shall be divided into the following classifications:” 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 flammable liquids?

In this corpus the term is used across 17 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 is the definition of flammable liquids?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IMC 2009 states, in Definitions: “Any liquid that has a flash point below 100°F (38°C), and has a vapor pressure not exceeding 40 psia (276 kPa) at 100°F (38°C). Flammable liquids shall be known as Class I liquids and shall be divided into the following classifications:” It is defined in IMC 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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