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Carbon Dioxide (CO2) is toxic, but the nature of the threat it poses is not always fully understood. Many national regulatory bodies set exposure limits above which employees must not be exposed. People die needlessly every year in tragic and completely avoidable accidents. Use of personal gas protection devices designed to detect CO2 is necessary to protect human life.

It is not possible to detect the presence of CO2 other than by use of gas detection equipment.

Properties and effects of CO2

CO2 is heavier than air. It is a hazard throughout the manufacturing process. If CO2 escapes, it will tend to sink to the floor, where it can form deadly, invisible pockets. It collects in cellars and at the bottom of containers and confined spaces, such as tanks and silos.

CO2 plant


• By displacing Oxygen (O2), leading to rapid asphyxiation: Asphyxiation can be caused by any gas displacing O2 leaving you with no O2 to breathe in the atmosphere
• As a toxin:

Not all gases are toxic. However, exposure to as little as 0.5% by volume CO2 represents a toxic health hazard. 2% can cause headaches, whilst 5% can cause major breathing problems.

Concentrations greater than 10% by volume can lead to death. Because CO2 is completely odourless and colourless, unless gas detection equipment is used, there may well be no indication of danger until it is too late

Exposure Limits

Studies show that even in the presence of normal concentrations of oxygen, exposures to 7% CO2 can cause death in only 5 minutes. While the data on the toxic effects of CO2 are interpreted slightly differently in different jurisdictions, there is little meaningful difference. Many countries set statutory workplace exposure limits to protect against the effects of a toxic gas.

These are generally defined in two ways:
• Short Term Exposure Limit (STEL) - maximum allowable concentration over a shorter time period, usually 15 minutes
• Long Term Exposure Limit (LTEL) - calculated as an 8-hour time weighted average (TWA).
The TWA for CO2 tends to be set around 0.5% with STEL between 1.5% and 3.0%. The TWA concept is based on a simple average of worker exposure during an 8 hour working day. It permits periods of exposure above the TWA limit, but only as long as the STEL is not exceeded and there is equivalent under-exposure to compensate.

Carbon Dioxide Displacement of Atmospheric Gases

There is still a misconception that by monitoring oxygen (O2) levels, you are effectively protecting against CO2. However, this is not the case, monitoring O2 levels will only help protect you against asphyxiation. Reliance on monitoring levels of oxygen to protect against CO2 could potentially lead to fatalities due to gas displacement.
Nitrogen (N2) comprises the majority of normal air at almost 80% volume. This means that, if a CO2 release occurs, most of the gas that it displaces will be N2.

Therefore, in the event of a leak of CO2, the percentage increase of CO2 is not matched by a similar decrease in the O2 concentration. CO2 can reach exposure limit levels, but O2 levels could still be comparatively unaffected and so considered safe.

Ensure compliance – Keep safe

In an environment where CO2 is used in many different ways and likely to be regularly encountered, even if at low levels, how can people be protected from being poisoned by CO2?

• Use gas detection equipment
In order to ensure compliance with occupational exposure limits calculated as TWAs, it is necessary to monitor the levels of CO2 each worker is exposed to individually through the use of personal gas detectors. Fixed gas detection systems can provide around the clock or continuous protection of the workplace.

Use of TWAs can also avoid false alarms, which cause unwarranted disruption. This prevents complacency which can lead to workers ignoring alarms or not turning on gas detectors. It should also improve operational efficiency.

• Detection in the breathing zone
A personal gas detector should monitor the air that the worker is inhaling. To do this effectively, it must be worn in the breathing zone (within 30 cm of the mouth). Attached to the clothing collar, a hard hat or breast pocket is ideal, however, not on a belt or trouser pocket. Breathing on it directly must be avoided as this could set the gas detector into alarm.

• User-friendly detection
A light and compact personal gas detector will encourage workers to wear it, comply and be protected. A bulky detector can be uncomfortable, heavy and restrict movement within a confined space which isn’t going to encourage the worker to wear it.

• Keep it simple

When it comes to keeping safe, consider using a personal gas detector with simple button operation and you should be comfortable with how to use the gas detector. Some gas detectors provide warning action messages in the event of an alarm so you know exactly what to do. This means that if the gas detector does go into alarm, workers will be better placed to respond fast.

• Don’t miss the warning signs
Some production areas are very noisy and poorly lit. A detector must combine powerful audible, vibration and visual signals to ensure the wearer is immediately alerted to danger, even in a noisy or dark environment.

• IR is best for CO2
Infrared (IR) sensors are better suited for industrial applications. IR sensors are not affected by high levels of gas, which some other gas sensors can be, making
them more accurate and reliable. IR sensors are more robust, too. They offer a much longer life compared, to other commonly used sensor types, which also makes them more cost-effective when used in a portable gas detector.

• Ensure reliability
Gas detectors are life-saving tools. For use in industrial environments, they must be tough to protect reliable electronics housed in impact-resistant casings.
While the need to leave gas sensors exposed to the atmosphere means that no instrument can be fully sealed, a high degree of protection against dust and water ingress is essential.

• Maintain
Whichever gas detector you choose, the importance of maintenance and calibration can’t be stressed enough. Regular bump testing (showing the gas detector gas) is the only way to check that a detector reacts correctly when in contact with gas. Personal gas detectors should also have a routine maintenance schedule which involves service, calibration and repair so it can be relied upon when needed.

Credit: Crowcon Instruments

Crowcon Tetra 3, yellow casingCrowcon Gasman CO2 detector, yellow casing

Do you need to detect CO2? Contact a1-cbiss to talk to our technical specialists for help with your gas detection needs