Good air critical for driver alertness
Staying alert at the wheel is obviously critical not only to your survival — but to that of others as well. A steady supply of fresh air can play a critical role in helping to keep a driver from nodding off.
Two factors come into play here — the recirculate position on the HVAC (heating, ventilation, air conditioning) system and air conditioning.
One of the biggest advances in air quality in recent years has also created one of the most dangerous situations — the recirculate feature.
This HVAC control or position, typically identified by a pictograph of the windshield or front of the vehicle with a curved arrow superimposed on it, has two purposes. 1. To allow occupants to close off the supply of outside air when in the presence of dirty air, e.g. a construction site or when in the vicinity of older diesel commercial vehicles and 2. to allow quicker heating or cooling of inside air.
The critical issue is closing off the outside air supply. By its very nature, recirculation involves breathing the same air over and over again.
Modern vehicles are very tight and while a certain amount of outside air is mixed in during the recirculation, the vast majority of the air you are breathing is the same stuff you previously exhaled.
With each breath, you are removing oxygen from and adding moisture to the air in the vehicle.
The reduced supply of fresh air contributes to the likelihood of nodding off, or falling asleep. This is especially dangerous in warmer weather when the sun falling directly on the occupants, combined with the lack of fresh air, creates an ideal environment for a snooze.
Even with the fan on full blast and the temperature set at meat locker levels, the diminished supply of fresh air is dangerous.
The other related issue involving recirculation is that the increased moisture it creates puts an extra strain on the system and results in fogged-up windows. Have you ever noticed how some vehicles, during that time of the year when the outside air is cooler, seem to have all the windows steamed up, some with water actually running down the side or rear windows?
I will guarantee you the air flow lever or button is in the recirculate position and has been for some time. With every breath, the occupants increase the humidity in the vehicle and when that moisture-laden air comes in contact with the cold glass, you get condensation.
I have known of situations with older vehicles, where the stale air becomes so bad the vehicle will start to smell, as the moisture settles into the carpets, underpad and other absorptive objects.
If you chose to use the recirculate feature, remember to return it to fresh air after the first few minutes of operation. Some of the more advanced system do this automatically — but make it a point to check yours.