Toxic and Asphyxiant Gases in Confined Spaces
Toxic and Asphyxiant Gases – Confined Space Hazards
Atmospheric hazards are one of the biggest risks when working in confined spaces.
Gases present in these environments can behave in different ways and have very different effects on the body.
Two of the most important types to understand are toxic gases and asphyxiant gases.
In this REAX training video, we explain how these gases behave and why monitoring the atmosphere is essential before and during confined space work.
Watch the full video:
Under normal conditions, the atmosphere around us contains approximately:
- 20.9% oxygen
- 79% nitrogen
- Small traces of other gases
When working in confined spaces, this balance can change.
Two major types of hazardous gases may be encountered:
Toxic gases
These gases mix with the atmosphere and affect the body when inhaled. Exposure can cause poisoning, respiratory distress and other systemic effects.
A common example is hydrogen sulphide, which is often detected using gas monitors measuring concentrations in parts per million (ppm).
Asphyxiant gases
Asphyxiant gases behave differently. Instead of poisoning the body directly, they displace oxygen from the atmosphere.
As oxygen levels drop, workers may experience:
- Fatigue
- Headaches
- Confusion
- Loss of consciousness
In confined spaces, this can occur quickly and often without obvious warning signs.
Practical Steps / Key Takeaways
When working in confined spaces, teams should consider the following:
- Understand what gases may be present before entry
- Use gas monitors to measure atmospheric conditions
- Monitor oxygen levels, toxic gases and other hazards
- Ensure adequate ventilation is in place
- Be prepared to exit immediately if alarms activate
It’s important to remember that hazardous gases are often invisible and odourless, making monitoring equipment critical for worker safety.
We emphasise the importance of understanding the environment before entering any confined space.
Gas monitoring equipment provides vital information, but workers must also understand what the readings mean and how different gases affect the body.
Training helps teams recognise atmospheric hazards, interpret gas monitor alarms and respond quickly if conditions become unsafe.
This knowledge is a key part of safe confined space planning and emergency preparedness.
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