What is the purpose of measuring CO in car parks?
Car parks are enclosed spaces, with often no natural ventilation and multiple levels with typically low ceilings. Toxic exhaust gases from vehicles can quickly accumulate, posing serious health risks. To protect both garage users and building occupants, a continuous monitoring is crucial.
Car gases
Despite the increasing shift toward electric mobility, the majority of cars in use today still rely on diesel or petrol engines. In general, these combustion engines primarily emit carbon dioxide (CO2) and carbon monoxide (CO) as exhaust gases. The relative amount of each gas can vary depending on several factors including the type of fuel, engine efficiency, and driving conditions.
Modern engines are designed to optimise the combustion process to produce as much CO2 as possible through complete combustion while minimising the production of carbon monoxide (CO) and other harmful emissions. In the presence of sufficient oxygen, the main by-products during combustion of hydrocarbon fuels in an engine are CO2 and water vapour (H2O). CO, on the other hand, is produced when incomplete combustion occurs due to insufficient oxygen supply, inefficient combustion, or engine malfunction. Typically, the emission of CO2 is much higher than the emission of CO.
CO, the silent killer
Carbon monoxide (CO) and carbon dioxide (CO2) are both colourless and odourless gases, consisting of one carbon atom and one or two oxygen atoms, respectively. However, CO is a much more potent pollutant in terms of immediate health effects. CO interferes with the body's ability to transport oxygen by attaching itself to red blood cells, preventing the uptake of oxygen. This can lead to symptoms including headaches, dizziness, nausea, drowsiness, vision problems, shortness of breath, and chest or stomach pain. High concentrations of CO can be life-threatening. Therefore, CO is often referred to as the silent killer.
The World Health Organization (WHO) has established guidelines for indoor CO exposure:
- 100 mg/m³ (15-minute average)
- 35 mg/m³ (1-hour average)
- 10 mg/m³ (8-hour average)
- 7 mg/m³ (24-hour average)
For ambient outdoor air, the WHO recommends a 24-hour average limit of 4 mg/m³.
Monitoring of CO
When CO molecules are released into open air, they typically react with oxygen to form CO2, following the reaction: 2 CO + O2 → 2 CO2
In this way, in outdoor environments, CO disperses quickly and its concentration drops to safer levels. However, in enclosed or poorly ventilated spaces like underground parking garages, CO can accumulate if vehicles or other sources continue to emit it. Without proper airflow, CO may build up to dangerous levels. Furthermore, CO tends to rise and can seep into upper levels of buildings, potentially exposing residents and office workers to harmful concentrations over time.
Therefore, local building codes and regulations often require CO sensors in parking facilities to monitor air quality and activate ventilation when needed. Compliance is not only crucial for safety but also to meet legal standards and avoid potential penalties.
CO2-based ventilation of parking garages
To reduce CO levels in enclosed areas, fresh air must be supplied to remove the gas. Smart ventilation systems use both CO and CO2 sensors to detect poor air quality and activate ventilation before gas concentrations reach dangerous levels. While the level of CO2 typically found in enclosed car parks is not considered to be dangerous, it can be measured as an indicator of other hazardous gases.
In situations where combustion is not efficient or there's a lack of proper air-to-fuel ratio, higher levels of CO will be generated along with other pollutants. However, CO2 sensors will be the first to detect poor air quality, long before the CO sensors notice increased values. When CO mixes with the air in an underground car park, CO2 concentrations will initially further increase.
To ensure effective monitoring, it’s important to understand the airflow patterns within the garage. Sensors should be placed in areas prone to CO build-up, such as spots with poor ventilation or stagnant air. Avoid installing sensors near walls or in corners, behind pillars or large objects, or in locations where the airflow to the sensor may be obstructed. This can lead to inaccurate readings and delay detection. CO sensors are typically mounted at breathing height — approximately 1.2 to 1.8 meters above the floor — where people are most likely to inhale the gas.
By monitoring CO2 concentrations, fans can be automatically controlled to maintain air quality by supplying fresh air and removing harmful gases in a timely manner.