After searching the web for the answer years ago, I could seldom find instances of death from suffocation while sleeping in your vehicle. Many sources claimed that vehicles are sufficiently leaky to prevent suffocation. But, let me share my story.
When sleeping in my vehicle (car camping), I usually crack two windows about an inch. On the evening of interest, myself and a friend were car-camping in the mountains at 9000 feet, where there is already a shortage of oxygen. Due to the demotivator of a couple of microbrews and the hassle of getting out of the back and into the cold air to grab keys, I unwisely decided to forgo the window-cracking protocol this particular evening.
Somewhat later that night, we both woke up — apparently both having some trouble sleeping. My friend (who is the kindest, most easy-going person you can imagine) commented that she felt irritable. I said, “That’s interesting, because astronaut Scott Kelley in his book “Endurance” (a year in the International Space Station) commented that whenever one of the CO2 absorption machines broke down, he got rather irritable as the CO2 in the air reached abnormally high levels.”
My friend attempted to light a lighter. It would not stay lit. The short-lived flame was long with a yellow tip, and separated from the top of the lighter by about a half inch. I opened the door to the car, and within a minute, the lighter was back to operating normally. The lighter does not measure CO2, but it is apparently a useful indicator of oxygen levels. If the oxygen level is low and humans are breathing the air, then the CO2 will be high. Neither high CO2 nor low oxygen are good things when they deviate from an accepted range.
CO2 occupies only 0.04% of normal air. When CO2 concentrations were even relatively low at 0.5% to 1%, “the International Space Station crew experienced headaches, lethargy, mental slowness, emotional irritation, and sleep disruption.” Oxygen is normally 21%, with nitrogen making up most of the rest. However, keep in mind that at high altitudes, less oxygen can be absorbed by the blood due to the lower air pressure.
After doing more research on the internet, I learned that cave explorers use the “lighter test” to see if the air is adequate for human consumption in a cave. I also found a chart that indicated that when the lighter behaves as explained above, the oxygen percentage is around 15%.
The moral to the story is: To avoid risk of suffocation while sleeping in your vehicle, leave the windows cracked when sleeping the night in a vehicle, especially if more than one person is breathing the air. At minimum, you don’t want yourself and your partner to get irritable, or even die!
riwhite