[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Forensic medicine](https://durgical.com/en/forensic-medicine/) › [Asphyxia and physical agents](https://durgical.com/en/forensic-medicine/areas/asphyxia-physical/) › Environmental asphyxia: low oxygen, gases and confined spaces

# Environmental asphyxia: low oxygen, gases and confined spaces

- Finding

In wells, tanks or bags the air can run out of oxygen or fill with gases; it leaves few findings and the scene is the key.

Updated Nov 13, 2026

## Key points

- In confined spaces, more than 60 per cent of deaths occur among would-be rescuers (NIOSH): nobody goes in without testing the air and without equipment.
- Oxygen can be used up (fermentation, rusting, bacteria) or displaced by other gases (nitrogen, carbon dioxide, methane, inert gases).
- Asphyxia in an oxygen-free atmosphere causes very rapid loss of consciousness, often without warning.
- Autopsy findings are scant and non-specific: the scene, air testing and toxicology decide.
- Some inert gases are not detected by routine toxicology: gas samples from the airway taken with a gas-tight syringe before the organs are opened are needed.

## What it is

Environmental asphyxia happens when the air being breathed has too little oxygen or contains gases that prevent its use. It occurs in confined spaces (wells, sewers, tanks, silos, ship holds, mines), where oxygen is used up or displaced by other gases, and in very small spaces, such as a plastic bag over the head. It can be accidental (work, children playing with bags or getting shut in), suicidal or, rarely, homicidal. The autopsy shows few findings, almost always non-specific, and some inert gases are not detected by routine tests, so the scene, the atmosphere and gas samples taken in time decide the diagnosis. Carbon monoxide has its own page.

## How to tell it apart

- Versus mechanical smothering: in environmental asphyxia there is no blockage of the mouth and nose by an outside force.
- Versus carbon monoxide poisoning: carboxyhaemoglobin is raised and livor may be cherry-red.
- Death of several people in the same space: suggests a dangerous atmosphere rather than an assault.
- A scene altered by relatives or rescuers (bag removed, gas turned off, container moved) can hide the mechanism: always ask how the body was found.

## How to recognise it

- Scene: a closed or poorly ventilated space, often several victims, including people who attempted a rescue.
- A plastic bag over the head, sometimes tied at the neck, or a connected gas container.
- Body: few external signs; there may be congestion and petechiae, which are non-specific.
- No signs of struggle in accidental and suicidal deaths.

## How it forms

- Breathing air with very little oxygen empties the blood of oxygen within a few breaths and the brain stops working.
- In a closed bag, oxygen falls and carbon dioxide rises with each breath.
- Some gases, such as hydrogen sulphide, are also toxic to cells.

## Next step: what to do and document

- Do not enter or let anyone enter a confined space until trained staff have tested and ventilated the air; call the fire service or the rescue team.
- Record the scene as found: space, ventilation, bag, gas containers and the body's position, with photographs.
- Request samples for full toxicology, including carboxyhaemoglobin, and, if an inert gas is suspected, gas samples from the trachea and lungs with a gas-tight syringe.
- Keep the bag, tubing and containers under chain of custody.
- In deaths at work, inform the competent authority so the work accident is investigated.

## Common mistakes

- Entering, or letting anyone enter, a confined space without testing the air and without breathing protection.
- Opening the chest before taking gas samples when an inert gas is suspected.
- Removing the bag or gas system without recording it in its original position.
- Concluding there was no asphyxia because the autopsy shows no findings.

## Test yourself

Think of the answer, then tap the question to see it.

## What proportion of deaths in confined spaces occurs among would-be rescuers, according to NIOSH?

More than 60 per cent; that is why nobody should enter without testing the air and without breathing protection.

## Why does the autopsy help little in environmental asphyxia?

Because the findings are scant and non-specific; the diagnosis depends on the scene, air testing and toxicology.

## How is inhalation of an inert gas that does not show on routine toxicology demonstrated?

With gas samples from the trachea and lungs taken with a gas-tight syringe before the chest is opened, analysed in a specialised laboratory.

## What does finding several people dead in the same well or tank suggest?

A dangerous atmosphere without oxygen or with toxic gases, in which the rescuers also succumbed.

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## Elsewhere in DurgiPedia

- [The causes of hypoxemia](https://durgical.com/en/physiology/the-causes-of-hypoxemia/)

## Connections

## Related 6

- [Mechanical asphyxia: types and the general signs](https://durgical.com/en/forensic-medicine/mechanical-asphyxia-types-and-the-general-signs/)
- [Smothering, gagging and choking](https://durgical.com/en/forensic-medicine/smothering-gagging-and-choking/)
- [Carbon monoxide deaths](https://durgical.com/en/forensic-medicine/carbon-monoxide-deaths/)
- [Autoerotic asphyxia](https://durgical.com/en/forensic-medicine/autoerotic-asphyxia/)
- [Forensic toxicology: which samples and how](https://durgical.com/en/forensic-medicine/forensic-toxicology-which-samples-and-how/)
- [The death scene: inspección técnica a cadáver (levantamiento)](https://durgical.com/en/forensic-medicine/the-death-scene-inspeccion-tecnica-a-cadaver/)

## Related conditions 3

- [Carbon monoxide poisoning](https://durgical.com/en/conditions/carbon-monoxide-poisoning/)
- [Cyanide poisoning](https://durgical.com/en/conditions/cyanide-poisoning/)
- [Suicidal behaviour and suicide risk](https://durgical.com/en/conditions/suicidal-behaviour-and-suicide-risk/)

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Educational content on forensic and legal medicine; not legal advice and no substitute for the technical guides of Colombia's National Institute of Legal Medicine and Forensic Sciences. Laws change: each page links the official text and says when it was last checked. For a real case, follow the guide in force and ask the competent authority.

Sources: [Preventing Occupational Fatalities in Confined Spaces (DHHS [NIOSH] Publication No. 86-110)](https://archive.cdc.gov/www_cdc_gov/niosh/docs/86-110/default.html) (National Institute for Occupational Safety and Health (NIOSH), 1986); [Investigating Confined Space Asphyxias: Plastic Bag Involvement and Gas Inhalation - A Case Series and Literature Review](https://pmc.ncbi.nlm.nih.gov/articles/PMC11887823/) (Acta Medica Lituanica, PubMed Central, 2024); [Helium Suicide, a Rapid and Painless Asphyxia: Toxicological Findings](https://pmc.ncbi.nlm.nih.gov/articles/PMC9412544/) (Toxics, PubMed Central, 2022).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/forensic-medicine/environmental-asphyxia-low-oxygen-gases-and-confined-spaces/