The automaker Hyundai announced that they now offer a CO2 sensor-controlled ventilation system in their 2015 Genesis model. Hyundai engineers claimed elevated carbon dioxide levels created by occupant respiration inside the vehicle cabin can cause drowsiness and slow reaction times. When the sensor detects CO2 levels above 2500 parts per million, it triggers the climate-control system to bring in more fresh air from outside.
Is what Hyundai says true? We did some research and discovered that while drowsiness accounts for between 10 and 30% of all automobile accidents and high CO2 levels are known to cause drowsiness, many people are not be aware of the importance of continually recirculating fresh air into their automobile.
Most cars have a “recirculate” button as part of the climate controls. This feature recirculates the auto cabin air instead of bringing in fresh air. It may be used to more quickly cool a hot car interior, or it may be used to keep odors and dust outside the car from entering the cabin.
While the recirculate feature can be useful, using it for even short periods can lead to high levels of CO2 in an closed car.
For example, a SAE International published a paper titled, "Modeling CO2 Concentrations in a Vehicle Cabin" documented the quick rise in CO2 levels in a passenger car cabin. Their data showed that CO2 levels can rise above 5,000ppm (OSHA limit) with the ventilation in recirculation mode.
In an article titled “The Drowsy Driving Off Switch”, Air Quality Consultant Dale Walsh recorded CO2 levels in a pickup truck cab rose quickly when the ventilation was set to recirculation mode.
Automobile manufacturers are aware of this data too, and that's why modern automobile cabins are engineered to continually provide enough fresh air to keep CO2 levels at or below 2,500ppm with a single driver. However, by turning “recirculate” on, the constant flow of fresh air is diminished, and CO2 buildup can result.
We were able to test this using a CO2Mini CO2 Monitor in our personal vehicles while driving back and forth to the office. The CO2Mini is powered via USB, so it is easy to plug into the car's USB port. Cars without a USB port used a standard USB accessory plug.
While high levels of CO2 in an enclosed car will never reach physically dangerous levels, they can have an impact on driver alertness. Therefore, it makes common sense to use the recirculate feature on your car for only short periods of time.