Building Code Glossary
Immediately Dangerous to Life or Health (IDLH): Building Code Definition
How the IMC 2009 define immediately dangerous to life or health (idlh), 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
Immediately dangerous to life or health (idlh) is a defined term in the International Mechanical Code (IMC) 2009, in Definitions. The code's own words are: “The concentration of airborne contaminants that poses a threat of death, immediate or delayed permanent adverse health effects, or effects that could prevent escape from such an environment. This contaminant concentration level is established by the National Institute of Occupational Safety and Health (NIOSH) based on both toxicity and flammability. It is generally expressed in …” 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 1 chapters of this corpus, most often in Definitions (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?
Immediately Dangerous to Life or Health (IDLH) — IMC 2009, Definitions:
The concentration of airborne contaminants that poses a threat of death, immediate or delayed permanent adverse health effects, or effects that could prevent escape from such an environment. This contaminant concentration level is established by the National Institute of Occupational Safety and Health (NIOSH) based on both toxicity and flammability. It is generally expressed in parts per million by volume (ppm v/v) or milligrams per cubic meter (mg/m3).
What must be verified before using this guidance?
Immediately Dangerous to Life or Health (IDLH) is defined once in this corpus, in the Definitions chapter of the International Mechanical Code (IMC) 2009:
The concentration of airborne contaminants that poses a threat of death, immediate or delayed permanent adverse health effects, or effects that could prevent escape from such an environment. This contaminant concentration level is established by the National Institute of Occupational Safety and Health (NIOSH) based on both toxicity and flammability. It is generally expressed in parts per million by volume (ppm v/v) or milligrams per cubic meter (mg/m3).
Where immediately dangerous to life or health (idlh) is used in the code
The term appears in 1 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Definitions | IMC 2009 | 1 |
Immediately Dangerous to Life or Health (IDLH) compared with Immediately Dangerous to Life and Health (IDLH)
These two are the closest pair in the 2009 I-Codes: about 63 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 | |
|---|---|
| Immediately Dangerous to Life or Health (IDLH) (IMC 2009) | airborne |
| Immediately Dangerous to Life and Health (IDLH) (IBC 2009) | air, borne, ifadequate, data, do, exist, precise, establishment, idlh, concentrations, independent, certified |
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 immediately dangerous to life or health (idlh) and immediately dangerous to life and health (idlh).
The terms immediately dangerous to life or health (idlh) is built out of
The definition above leans on 1 other defined term. Each carries its own code definition, and a local amendment to any of them changes what immediately dangerous to life or health (idlh) covers:
- Meter — IRC 2009: The instrument installed to measure the volume of gas delivered through it.
Immediately Dangerous to Life or Health (IDLH): 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 | Definitions (IMC 2009) | |
| Confirm the dependent definition | Meter | |
| 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
- Meter: Building Code Definition
- Building: Building Code Definition
- Construction Documents: Building Code Definition
- Registered Design Professional: 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 immediately dangerous to life or health (idlh)?
The International Mechanical Code (IMC) 2009 defines it in Definitions as: “The concentration of airborne contaminants that poses a threat of death, immediate or delayed permanent adverse health effects, or effects that could prevent escape from such an environment. This contaminant concentration level is established by the National Institute of Occupational Safety and Health (NIOSH) based on both toxicity and flammability. It is generally expressed in parts per million by volume (ppm v/v) or milligrams per cubic meter (mg/m3).” 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 immediately dangerous to life or health (idlh)?
In this corpus the term is used across 1 chapters, led by Definitions in the IMC 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.
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