Sleeping in a car does not usually cause asphyxiation if the windows are open, but sleeping in a closed car for a long time is a risk of asphyxiation. First of all, the closed car air circulation is poor, the body exhaled carbon dioxide can not be timely out of the car, if coupled with the summer heat factor, the temperature inside the car can sometimes even reach 60 degrees Celsius, this environment in the car sleep is prone to asphyxiation. In addition, when the car engine is working, it needs to burn gasoline, which consumes oxygen, and incomplete combustion of gasoline can produce carbon monoxide. When the doors and windows are closed and the car is in an airtight environment, the carbon monoxide produced by the engine enters the car through the gaps between the air conditioner and the car, which can cause asphyxiation when the concentration of carbon monoxide is too high.