Carbon Dioxide (CO₂)
Carbon Dioxide (CO₂): Risks, Detection, Exposure Levels, and Monitoring
What is carbon dioxide (CO₂)?
Carbon dioxide (CO₂) is a colorless, odorless gas that occurs naturally in the atmosphere at low concentrations (around 0.04%). While it is harmless at typical levels, elevated concentrations can pose serious health risks and, in confined or poorly ventilated spaces, may be fatal.
CO₂ cannot be detected by human senses, even at high concentrations, so it must be measured using dedicated carbon dioxide monitoring equipment.
Why carbon dioxide is dangerous?
Carbon dioxide is often referred to as a “silent killer” because:
- It cannot be seen, smelled, or tasted
- It can accumulate without being noticed
- Symptoms develop gradually over time
In most workplaces and indoor environments, people are the primary source of carbon dioxide. While these levels are typically within safe limits, elevated CO₂ can still lead to feelings of fatigue and drowsiness, even when those present are contributing to the increase.
In environments where CO₂ is stored or used, such as breweries, laboratories, or food production facilities, leaks can rapidly create dangerous concentrations.
Because CO₂ is more dense than air, it tends to settle in low-lying areas. This significantly increases risk in confined spaces. A person entering an area with high CO₂ levels may lose consciousness and collapse, where concentrations are even higher, leading to asphyxiation.
In severe cases, carbon dioxide exposure can result in:
- Loss of consciousness
- Asphyxiation
- Fatality
Carbon dioxide exposure levels and effects
| CO₂ Concentration | Effect |
| 250–350 ppm | Normal outdoor air |
| 350–1,000 ppm | Typical indoor air |
| 1,000–2,000 ppm | Drowsiness, reduced air quality |
| 2,000–5,000 ppm | Headaches, dizziness, increased heart rate |
5,000 ppm - U.S. long-term exposure limit (8 hours, OSHA PEL)
15,000 ppm - U.S. short-term exposure limit (STEL)
Even moderate increases can affect comfort and performance, while higher concentrations pose serious health risks.
Where is carbon dioxide found?
Carbon dioxide is present across a wide range of environments, including:
Everyday environments
- Indoor air (generated by human respiration)
- Poorly ventilated offices
- Confined or enclosed spaces
Industrial and commercial environments
- Beverage and brewery operations
- Restaurants and storage cellars
- Laboratories and medical facilities
- Food and beverage production
- Dry ice storage and transportation
- Gas and welding supply operations
In these environments, CO₂ is often stored under pressure, which increases the risk of leaks and the potential for hazardous concentrations to develop.
Why CO₂ monitoring is essential
Where carbon dioxide is used or stored, effective monitoring is essential for:
- Protecting employees and site visitors
- Maintaining compliance with safety regulations
- Reducing the risk of potentially fatal incidents
A common misconception is that oxygen monitors can be used as a substitute for CO₂ monitoring.
This is not correct.
CO₂ can reach dangerous concentrations well before oxygen levels fall enough to trigger an oxygen alarm. As a result, a leak may go undetected until it becomes a serious hazard.
How carbon dioxide is detected
Carbon dioxide must be measured using dedicated CO₂ sensors, typically based on the following technologies:
- NDIR (Non-Dispersive Infrared)
- Detects CO₂ by measuring infrared light absorption
- Highly accurate and widely used
Gas Filter Correlation (GFC)
- Highly selective
- Minimizes interference from other gases
These sensing technologies enable precise and reliable measurement of CO₂ concentrations in air.
Where should CO₂ sensors be installed?
Because CO₂ is denser than air:
CO₂ sensors should be installed low to the ground, typically 12-18 inches above floor level
Positioned close to potential leak sources (e.g., cylinders)
This helps ensure leaks are detected early, before gas accumulates at breathing height.
Common safety mistakes
Some of the most common and most dangerous mistakes include:
- Using a carbon monoxide detector instead of a CO₂ monitor
- Relying on oxygen monitors to detect CO₂ leaks
- Installing sensors at the wrong height
- Assuming CO₂ can be detected by smell
These errors can lead to undetected exposure and significant safety risks.
Industry applications
Carbon dioxide monitoring is essential across a wide range of industries:
Beverage & Hospitality
- Cellars, bars, and restaurants
- CO₂ used in carbonation systems
- Increased risk to occupant health in venues designed for dining and large gatherings, such as restaurants, hotels, and stadiums, requiring compliance with fire codes and safety regulations
Dry Ice Storage & Use
- Dry ice is used to preserve food and medical supplies during transportation, as well as for cleaning military and industrial equipment, vehicles, and ships in a process known as “dry ice blasting”
- As solid carbon dioxide, dry ice sublimates directly into gas. In enclosed or poorly ventilated spaces, this can quickly lead to dangerous CO₂ concentrations, posing a risk of poisoning or fatality
Laboratories & Medical
- CO₂ used in surgical procedures and laboratory equipment, including incubators
- Strict safety and monitoring requirements
Agriculture & Cultivation
- CO₂ used to enhance plant growth
- Increased risk in sealed or controlled grow environments
Gas Distribution & Welding
- Gas and welding operations regularly involve exposure to hazardous gases
- Processes may release gases such as helium (He), argon (Ar), and CO₂, which at high concentrations can displace oxygen and create asphyxiation risks
- CO₂ and other gases are stored and transported under pressure, increasing the risk of leaks in storage and handling areas
Recommended monitoring solutions
To help ensure safety, both fixed and portable monitoring systems should be considered:
Fixed monitors for continuous area monitoring
Portable monitors for personal protection
Selecting the right solution depends on several factors, including:
The environment
How gas is used or stored
The level of risk present
Analox offers a range of products for CO₂ monitoring, including:
Related products
Related Sectors
FAQs
Can you smell carbon dioxide?
No. CO₂ is colorless and odorless, meaning it cannot be detected by human senses.
Can an oxygen monitor detect CO₂ leaks?
No. Oxygen monitors measure oxygen levels, not carbon dioxide. CO₂ can reach dangerous concentrations before an oxygen alarm is triggered.
Where should CO₂ detectors be placed?
Typically installed low to the ground (around 12 inches above the floor), as CO₂ is denser than air.
Is CO₂ always dangerous?
No. It is safe at normal atmospheric levels but becomes hazardous at higher concentrations, especially in confined spaces.
Key Takeaway
Carbon dioxide is a common but potentially hazardous gas that cannot be detected without specialized monitoring equipment.
In any environment where CO₂ is stored or used, dedicated gas monitoring is essential to maintain safety and help prevent potentially fatal incidents.