Research from University of Leicester Physics students has found that smoking in a car for 75 minutes could leave you unconscious.
They estimated the consequences of smoking tobacco cigarettes in a car and how much opening a window would reduce the risk of carbon monoxide (CO) poisoning.
They calculated that you would need to smoke 15 cigarettes in 75 minutes for the level of carbon monoxide to reach levels of 1000 parts per minute – enough to make you fall unconscious.
If it takes five minutes to smoke one cigarette, then it would take at least 75 minutes to fill the car with this amount of harmful carbon monoxide, causing loss of consciousness.
It was announced earlier this month that drivers in England will be banned from smoking in their cars from October if they are carrying children as passengers.