Maybe it was not CO.....maybe it was just simply the exhaust.....I just know that there were problems here not too long ago resulting from exhaust getting into the attic via the vents. Just to clarify prior to it being queried, it was not any job I was associated with.
Isn't CO the prime component of concern in the exhaust? Next biggest problem would be unburned fuel in the exhaust but primarily only if the engine has some problems resulting in this situation. The smell could be annoying especially with a diesel engine but is not necessarily a health concern as compared to CO.
My point was that ventilation in attics typically draws air in from lower level vents and simple convection of warm air rising pulls it upward to where it exits out of another ventilation opening. A mechanical system uses fans to increase the amount of air that is circulated but still ordinarily draws air in from a low level and it exits at a high level.
Now if you are getting unwanted air into the living space via the attic you have to have some kind of ventilation system that is pulling air out of the living space and there is not enough make up air from elsewhere, and it is creating negative pressure within the living space and pulling air in every opening available - including any path to the attic.
This kind of problem is more common in commercial kitchens where they have exhaust fans pulling a pretty fair volume of air out of the building - but they have not made provisions to allow make up air to enter somewhere. If the building is sealed pretty well then you have suction at every door and window. Sometimes great enough that doors are difficult to open.
