32.
The interior of the vehicle is sealed completely from the outside, so any noxious chemicals around the car can not filter in. This is just another of the many layers and sublayers of protection against any potential danger that can be imagined. Especially when the Presidential Car travels out of the country so often, any and every precaution needs to be taken. The fact that the windows don’t open and the doors are 7-inches thick aids this effort greatly.