# Immediately Dangerous to Life and Health (IDLH): Building Code Definition

> How the IBC 2009, IFC 2009 define immediately dangerous to life and health (idlh), where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/immediately-dangerous-to-life-and-health-idlh/
- Last updated: 2026-09-07
- Data source: 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.

## Key facts

| Fact | Value |
| --- | --- |
| Defined in | IBC 2009, IFC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IBC 2009 Special Detailed Requirements Based on Use and Occupancy (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 7 (counted across the codes hosted here) |
| Wording identical across codes | No (compare before citing one code's wording under another) |

## Direct answer

Immediately dangerous to life and health (idlh) is a defined term in the International Building Code (IBC) 2009, in Special Detailed Requirements Based on Use and Occupancy. The code's own words are: “The concentration of air-borne contaminants which 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 generally is expressed in …” The IFC 2009 defines the same term with different wording, so the controlling text depends on which code governs the question in front of you — the comparison below sets the versions side by side. The term is used in 7 chapters of this corpus, most often in Special Detailed Requirements Based on Use and Occupancy (IBC 2009), Semiconductor Fabrication Facilities (IFC 2009), Compressed Gases (IFC 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](https://nz.linkedin.com/in/barrington), Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.*

## What does this term mean?

**Immediately Dangerous to Life and Health (IDLH)** — IBC 2009, Special Detailed Requirements Based on Use and Occupancy:

> The concentration of air-borne contaminants which 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 generally is expressed in parts per million by volume (ppm v/v) or milligrams per cubic meter (mg/m3). Ifadequate data do not exist for precise establishment of IDLH concentrations, an independent certified industrial hygienist, industrial toxicologist, appropriate regulatory agency or other source approved by the bUilding official shall make such determination.

![Labeled code-term definition diagram: Immediately Dangerous to Life and Health (IDLH): Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/immediately-dangerous-to-life-and-health-idlh/diagram-1344.webp)

*How the IBC 2009, IFC 2009 define immediately dangerous to life and health (idlh), where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

Two of the I-Codes in this corpus define **Immediately Dangerous to Life and Health (IDLH)**, and the wording is not identical — read the version that governs your question.

| Code | Where it is defined | Definition |
| --- | --- | --- |
| IBC 2009 | [Special Detailed Requirements Based on Use and Occupancy](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/special-detailed-requirements-based-on-use-and-occupancy.md) | The concentration of air-borne contaminants which 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 generally is expressed in parts per million by volume (ppm v/v) or milligrams per cubic meter (mg/m3). Ifadequate data do not exist for precise establishment of IDLH concentrations, an independent certified industrial hygienist, industrial toxicologist, appropriate regulatory agency or other source approved by the bUilding official shall make such determination. |
| IFC 2009 | [Hazardous Materials-general Provisions](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/hazardous-materials-general-provisions.md) | The concentration of air-borne 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 generally is expressed in parts per million by volume (ppm v/v) or milligrams per cubic meter (mg/m3). Ifadequate data do not exist for precise establishment of IDLH concentrations, an independent certified industrial hygienist, industrial toxicologist, appropriate regulatory agency or other source approved by the fire code official shall make such determination. |

## Where immediately dangerous to life and health (idlh) is used in the code

The term appears in 7 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Special Detailed Requirements Based on Use and Occupancy](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/special-detailed-requirements-based-on-use-and-occupancy.md) | IBC 2009 | 4 |
| [Semiconductor Fabrication Facilities](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/semiconductor-fabrication-facilities.md) | IFC 2009 | 3 |
| [Compressed Gases](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/compressed-gases.md) | IFC 2009 | 2 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 1 |
| [Fire Protection Systems](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-protection-systems.md) | IBC 2009 | 1 |
| [Definitions](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/definitions.md) | IFC 2009 | 1 |
| [Hazardous Materials-general Provisions](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/hazardous-materials-general-provisions.md) | IFC 2009 | 1 |

## Immediately Dangerous to Life and Health (IDLH) compared with Immediately Dangerous to Life or 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 and Health (IDLH)** (IBC 2009) | air, borne, ifadequate, data, do, exist, precise, establishment, idlh, concentrations, independent, certified |
| [Immediately Dangerous to Life or Health (IDLH)](https://harth.build/resources/glossary/immediately-dangerous-to-life-or-health-idlh.md) (IMC 2009) | airborne |

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 and health (idlh) and immediately dangerous to life or health (idlh).

## The terms immediately dangerous to life and health (idlh) 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 immediately dangerous to life and health (idlh) covers:

- **[Fire Code Official](https://harth.build/resources/glossary/fire-code-official.md)** — IFC 2009: The fire chief or other designated authority charged with the administration and enforcement of the code, or a duly authorized representative.
- **[Building Official](https://harth.build/resources/glossary/building-official.md)** — IBC 2009: The officer or other designated authority charged with the administration and enforcement of this code, or a duly authorized representative.
- **[Code Official](https://harth.build/resources/glossary/code-official.md)** — IRC 2009: The officer or other designated authority charged with the administration and enforcement of this code, or a duly authorized representative.
- **[Building](https://harth.build/resources/glossary/building.md)** — IBC 2009: Any structure used or intended for supporting or sheltering any use or occupancy.
- **[Approved](https://harth.build/resources/glossary/approved.md)** — IBC 2009: Acceptable to the code official or authority having jurisdiction.

## Immediately Dangerous to Life and Health (IDLH): what to open, and in what order

Every row is a document this term depends on. The [ICC code library](https://codes.iccsafe.org/codes) and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) cover the middle rows.

| Check | Where | Confirmed |
| --- | --- | --- |
| Read the definition in the adopted IBC | Special Detailed Requirements Based on Use and Occupancy | |
| Read the definition in the adopted IFC | Hazardous Materials-general Provisions | |
| Re-check the requirement that uses it | Special Detailed Requirements Based on Use and Occupancy (IBC 2009) | |
| Re-check the requirement that uses it | Semiconductor Fabrication Facilities (IFC 2009) | |
| Re-check the requirement that uses it | Compressed Gases (IFC 2009) | |
| Re-check the requirement that uses it | Definitions (IBC 2009) | |
| Confirm the dependent definition | Fire Code Official | |
| Confirm the dependent definition | Building Official | |
| Confirm the dependent definition | Code Official | |
| 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](https://harth.build/resources/glossary.md)
- [Fire Code Official: Building Code Definition](https://harth.build/resources/glossary/fire-code-official.md)
- [Building Official: Building Code Definition](https://harth.build/resources/glossary/building-official.md)
- [Code Official: Building Code Definition](https://harth.build/resources/glossary/code-official.md)
- [Building: Building Code Definition](https://harth.build/resources/glossary/building.md)

## 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](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.

### Source links

- [codes.iccsafe.org](https://codes.iccsafe.org/codes)

- [iccsafe.org](https://www.iccsafe.org/advocacy/code-adoption-maps/)

## Frequently asked questions

### What is the code definition of immediately dangerous to life and health (idlh)?

The International Building Code (IBC) 2009 defines it in Special Detailed Requirements Based on Use and Occupancy as: “The concentration of air-borne contaminants which 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 generally is expressed in parts per million by volume (ppm v/v) or milligrams per cubic meter (mg/m3). Ifadequate data do not exist for precise establishment of IDLH concentrations, an independent certified industrial hygienist, industrial toxicologist, appropriate regulatory agency or other source approved by the bUilding official shall make such determination.” 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 and health (idlh)?

In this corpus the term is used across 7 chapters, led by Special Detailed Requirements Based on Use and Occupancy in the IBC 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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