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Ventilation of Parking Garages

20/02/2024 Yves Vinck

Indoor air quality is a critical concern, particularly in enclosed spaces like parking garages where vehicular emissions can impact the environment and occupant health. In our quest to ensure safety and optimal conditions within these spaces, we delve into the importance of monitoring carbon monoxide (CO) and carbon dioxide (CO2) levels.

Ventilation of Parking Garages
In general, cars with combustion engines primarily emit carbon dioxide (CO2) and carbon monoxide (CO) as exhaust gases. However, the relative amounts of each emitted gas can vary depending on several factors such as the type of fuel used, the efficiency of the engine, and the driving conditions. Due to their typically low ceiling, underground and enclosed car parks present a particular challenge to ventilation systems. Such a smart ventilation system must prevent the accumulation of toxic gases from motor exhausts in a garage. Toxic gas sensors are optimized to detect and measure these toxic gases in parking garages.
Typically, carbon dioxide (CO2) is emitted in larger quantities compared to carbon monoxide (CO) in combustion engine exhaust. This is because carbon dioxide is a byproduct of the complete combustion of hydrocarbon fuels such as gasoline or diesel. On the other hand, carbon monoxide is produced when there is incomplete combustion of fuel due to insufficient oxygen supply, inefficient combustion, or engine malfunction.
In terms of comparison, carbon dioxide emissions from combustion engines are generally much higher than carbon monoxide emissions. However, it's important to note that carbon monoxide is a more potent pollutant in terms of immediate health effects, as it can interfere with the body's ability to transport oxygen. Therefore, even though CO2 emissions are higher and therefore easier to detect, CO emissions are more concerning in terms of immediate health impacts. For this reason, CO sensors are sometimes prescribed in local regulations for monitoring air quality in parking garages. However, controlling a ventilation system in parking garages can be done much more efficiently based on CO2 measurements. When vehicles with combustion engines are active, CO2 sensors will be the first to detect poor air quality, long before the CO sensors notice increased values. Based on the CO2 measurement, the fans can be controlled to supply fresh air and remove toxic gases in a timely manner.
The risk of Carbon Monoxide (CO), the silent killer
Toxic or noxious gases are gases that are harmful to living things. Carbon monoxide (CO) is a colourless, odourless and highly poisonous gas. It is sometimes referred to as the ‘silent killer’. It is emitted by vehicle engines together with CO2. When carbon monoxide molecules are released into open air, they typically undergo oxidation reactions. It does dissipate relatively quickly when exposed to fresh air.  In the presence of oxygen (O2), carbon monoxide can react to form carbon dioxide (CO2). The reaction can be represented as: 2 CO + O2 → 2 CO2. When CO mixes with air in an underground parking garage, it will initially further increase CO2 concentrations. When released into open spaces or outdoor environments, CO tends to disperse and mix with the surrounding air, reducing its concentration to safer levels.

However, in enclosed or poorly ventilated spaces like parking garages, CO can accumulate if there is ongoing emission from vehicle exhaust or other sources without adequate ventilation. Without proper airflow, the gas may linger and build up to dangerous concentrations, posing health risks to individuals in those areas, which can lead to headaches, dizziness, nausea, and in severe cases, it can be life threatening. When CO is breathed in, it gets into the blood stream, attaching itself to red blood cells, which can then no longer carry oxygen. We humans need oxygen to break down food in order to get the energy we need to survive, to move our muscles or even to just think. Symptoms of CO poisoning are headaches, drowsiness, visual problems, breathlessness, nausea and even stomach and chest pains. To prevent or reduce high concentrations of carbon monoxide in an enclosed environment as an underground parking, fresh air should be supplied to wash away the carbon monoxide. 

Regular monitoring of CO levels in parking garages is crucial for maintaining safety standards and safeguarding occupants' health. It aids in the timely detection of potential leaks or inadequate ventilation, enabling interventions to mitigate health risks associated with CO exposure. Depending on local regulations and standards, there might be specific requirements for monitoring CO levels in enclosed spaces like parking garages. Regular monitoring helps ensure compliance with these regulations.
Where to install the CO sensors?
When positioning carbon monoxide (CO) sensors in indoor spaces such as underground parking garages, it's generally recommended to install them at a height where they can effectively detect CO concentrations that pose a risk to occupants. Unlike LPG, which is denser than air and tends to accumulate near the ground, CO is roughly the same density as air and distributes evenly throughout the space. Therefore, CO sensors are usually installed at breathing height, roughly between 1.2 to 1.8 meters above the ground, as this is where people typically breathe.
Understanding the airflow patterns within the parking garage is crucial for effective sensor placement. If there are specific areas where CO buildup is more likely due to poor ventilation or stagnant air, sensors should be strategically located to monitor these areas. Sensors should be placed in locations free from obstructions that could interfere with the flow of CO to the sensor. Avoid placing sensors near walls, corners, or behind objects that could block airflow and result in inaccurate readings. 
Local building codes or regulations may specify requirements for the placement of CO sensors in parking garages or other indoor spaces. Compliance with these regulations is essential for ensuring the safety of occupants and avoiding potential penalties.
The Role of Carbon Dioxide (CO2) monitoring
Carbon Dioxide or CO2 is a greenhouse gas that is natural and harmless in small quantities. It is necessary for the survival of life on earth. CO2 is not only the result from burning fossil fuels. Indoor carbon dioxide concentrations are the result of a combination of outdoor CO2, indoor breathing and the ventilation rate of the building. CO2 is evacuated by supplying fresh air. While carbon dioxide (CO2) isn't as immediately harmful as CO, it plays a significant role in assessing overall indoor air quality and ventilation system effectiveness.
CO2 ranges
When a motor combusts fuel, the primary products of combustion are carbon dioxide (CO2) and water vapor (H2O) in the presence of sufficient oxygen. The amount of CO2 released during combustion is generally higher than the amount of carbon monoxide (CO) produced. Under normal operating conditions, modern engines and combustion systems 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. However, in situations where combustion is not efficient or there's a lack of proper air-to-fuel ratio, higher levels of carbon monoxide can be generated along with other pollutants.

Elevated CO2 levels can cause discomfort, leading to headaches and a feeling of stuffiness. Monitoring CO2 levels ensures adequate ventilation and helps maintain acceptable indoor air quality for the comfort and well-being of individuals using or working in the parking garage. To prevent or reduce high concentrations of carbon dioxide in an enclosed environment as an underground parking, fresh air should be supplied to wash away the carbon dioxide. Indoor CO2 levels between 400-1.000 ppm are acceptable. When the values exceed this range, additional ventilation is required.
LPG measurements to detect dangerous situations
LPG or Liquefied Petroleum Gas is highly flammable, and in the confined space of an underground parking garage, any leakage can pose a significant fire hazard. LPG is commonly used as a fuel for vehicles and as a heating source. In underground parking garages, there's a risk of leaks from vehicles or from the storage systems themselves. Vehicles with an LPG tank are therefore not allowed in all parking garages. Measuring LPG levels helps to detect any leaks promptly and to enable the monitoring of potentially dangerous concentrations. 
Underground parking garages are often used by a large number of people, including drivers, pedestrians, and maintenance staff. Monitoring LPG levels ensures the safety of occupants by alerting them to any hazardous conditions and allowing for timely evacuation if necessary. Many jurisdictions have regulations governing the use and storage of LPG in public spaces such as parking garages. Regular monitoring and measurement of LPG levels help ensure compliance with these regulations, reducing the risk of fires and explosions, including the risk of penalties and liability in case of accidents.
When measuring LPG levels in an underground parking garage, it's essential to position the sensors at a height where the gas concentration is likely to be most representative of the overall environment and where it poses the most significant risk to occupants. Generally, this means placing the sensors approximately 30 cm above floor level. LPG is denser than air, meaning it tends to settle near the ground rather than dispersing upwards. Placing sensors closer to the ground allows for more accurate detection of any LPG leaks, as the concentration will be highest near the floor where the gas accumulates.
However, it's essential to consider the specific layout and ventilation characteristics of the parking garage when determining sensor placement. For example, if there are ventilation ducts or fans that could affect gas dispersion patterns, sensors may need to be strategically placed to account for these factors. Consulting with safety experts or engineers familiar with gas detection systems can help ensure the most effective placement of LPG sensors in an underground parking garage.

CO2 based ventilation control in parking garages
Given the immediate health risks associated with high CO concentrations, prioritising CO measurement is often recommended in closed parking garages. CO can quickly reach hazardous levels in confined spaces, necessitating vigilant monitoring to prevent potential health hazards. However, CO2 measurement remains valuable for assessing overall indoor air quality and ventilation system efficiency. Since more CO2 is released during combustion processes, CO2 will often be detected faster than CO presence in the air. Both CO and CO2 measurements work synergistically to provide insights into the environment's health and safety aspects. 
Air quality is the basis on which a ventilation system is controlled. When the air quality is insufficient, more ventilation is required. The fresh air will flush out the toxic gases. CO2 sensors provide a more accurate indication of air quality and will respond much faster than CO sensors. Controlling jet fans in a parking garage with CO sensors will lead to delayed responses, resulting in poor air quality and insufficient ventilation.
We can conclude that CO2 sensors are needed to guarantee good air quality in an underground parking garage. When vehicles with combustion engines are active, CO2 sensors will be the first to detect poor air quality, long before the CO sensors notice increased values. Based on the CO2 measurement, the fans can be controlled to supply fresh air and remove toxic gases in a timely manner. CO sensors can be used to identify dangerous situations in case the ventilation system does not function correctly.
We at Sentera offer sensors that are specifically designed for installation in such enclosed spaces.
The SPRKM-R is a multifunctional transmitter that measures CO, temperature, relative humidity as well as LPG.
Our outdoor CO2 sensors are created as such that they can be applied in harsh environments, providing IP65 protection against ingress of water and dust.
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