Underground parking garages present a unique challenge for ventilation systems. These enclosed spaces typically have low ceilings and limited natural airflow, allowing exhaust gases from vehicles to accumulate quickly. Without effective monitoring and ventilation, this can pose serious health risks to garage users, maintenance staff, and even building occupants above the garage.
A smart ventilation strategy is therefore essential to ensure safe air quality in a timely and energy-efficient manner
Exhaust gases in parking garages
Despite the increasing shift toward electric mobility, the majority of cars in use today still rely on diesel or petrol engines. These combustion engines primarily emit carbon dioxide (CO2) and carbon monoxide (CO) as exhaust gases. The relative amount of each gas depends on factors such as fuel type, engine efficiency and driving conditions.
In the presence of sufficient oxygen, the main by-products of the combustion of hydrocarbon fuels 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. Modern engines are designed to optimise combustion and produce as much CO2 as possible through complete combustion. As a result, CO2 emissions are typically much higher than CO emissions. However, even at relatively low concentrations, CO poses a far greater immediate health risk.
Liquefied Petroleum Gas (LPG) is also commonly used as a vehicle fuel and for heating. LPG is highly flammable and even a small leak can create a serious fire or explosion risk in confined spaces such as underground parking garages. Leaks may occur from vehicles or fuel systems, which is why vehicles equipped with LPG tanks are not permitted in all parking garages. Continuous LPG monitoring allows early detection and timely intervention, ensuring the safety of both occupants and infrastructure, and compliance with safety regulations.
Because LPG is heavier than air, it tends to accumulate near the floor. LPG sensors are therefore typically installed close to ground level – approximately 30 cm above floor – to ensure accurate and timely detection. Sensor placement should always take the specific layout and ventilation characteristics of the parking garage into account to ensure reliable monitoring and maximum safety.
The risk of carbon monoxide (CO), the silent killer
Carbon monoxide (CO) is a colourless, odourless and highly toxic gas, often referred to as the silent killer. When inhaled, CO binds to red blood cells and prevents them from transporting oxygen through the body. This can cause headaches, dizziness, fatigue, nausea, drowsiness, visual disturbances and shortness of breath. At higher concentrations, CO exposure can quickly become life-threatening.
In open air, CO disperses relatively quickly and reacts with oxygen to form CO2 – following the reaction: 2 CO + O2 → 2 CO2.
In enclosed or poorly ventilated environments such as underground parking garages, however, CO can accumulate rapidly if emissions continue without sufficient fresh air supply. In addition, CO can rise and migrate into upper building levels, potentially exposing residents or office workers above the garage to harmful concentrations over time.
For this reason, local building codes and regulations often require CO sensors in parking facilities. Continuous CO monitoring helps ensure regulatory compliance but, more importantly, safeguards occupant health by activating ventilation when dangerous levels are detected.
Where to install CO sensors?
Accurate detection depends strongly on correct sensor placement. Because CO has a similar density to air, it distributes evenly throughout the space. CO sensors are therefore typically installed at breathing height, between 1.2 and 1.8 metres above the floor.
Sensors should be positioned in areas where gas build-up is most likely, such as zones with limited airflow or poor ventilation. Locations near walls, corners, pillars or other obstructions should be avoided, as restricted airflow can delay detection and lead to inaccurate readings.
The role of CO2-based ventilation control in parking garages
Smart ventilation systems use both CO and CO2 sensors to detect poor air quality in parking garages and activate ventilation before gas concentrations reach dangerous levels.
Because high CO concentrations represent an immediate and severe safety risk, monitoring CO is typically prioritized in enclosed parking garages. CO – and other pollutants – can quickly reach hazardous levels in confined spaces and to flush out these toxic gases, fresh air needs to be supplied.
CO2 is a well-known and excellent indicator of overall air quality and ventilation effectiveness. Although typical CO2 levels in parking garages are not immediately hazardous, elevated concentrations are a reliable indicator of deteriorating air quality. Indoor CO2 levels between approximately 400 and 1000 ppm are generally considered acceptable. When levels rise above this range, additional ventilation is required.
Since CO2 is produced in much larger quantities during combustion, CO2 sensors will be the first to detect and respond to changes in air quality, long before the CO sensors notice increased values. Additionally, when released CO mixes with the air in an underground car park, it will form extra CO2 leading to a further increase of the CO2 concentrations. Controlling jet fans in a parking garage with only 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. By using CO2 monitoring to control jet fans or exhaust systems, fresh air can be supplied in a timely and energy-efficient manner, preventing the build-up of toxic gases. CO sensors then act as a critical safety layer, identifying dangerous situations in case the ventilation system does not function correctly.
Complete ventilation solution for parking garages
At Sentera, we offer sensors specifically designed for enclosed and demanding environments such as parking garages. Our solutions support smart ventilation systems that protect people, property and air quality.
Effective ventilation in underground parking garages relies on a combination of CO₂ and CO monitoring:
- CO2 sensors ensure good air quality and enable efficient, demand-driven ventilation
- CO sensors protect against acute health risks
The ISCMG2-4 is our new, efficient and accurate CO sensor with an IP31 protection against the ingress of water and dust.
Our outdoor CO2 sensor is designed for harsh environments and provide IP65 protection.