In many locations there are no mechanical codes, nor are contractors required to be licensed. Fire departments are called in to take reading on instruments which record only the presence of CO with no clues as to its cause. Often the fire department is called after windows and doors are opened and the carbon monoxide dispersed, resulting in no readings at all. Some medical personnel are not aware of the possible extent of the problem and may misdiagnose what on the surface looks like a simple case of the flu. Carbon monoxide kills by replacing oxygen in the blood.
High levels kill in a short period.
Moderate levels, because CO is a cumulative poison, can cause misdiagnosed health problems or even death. Low levels over a long period can cause health problems, especially for patients at risk. Exposure can result in long lasting or permanent effects including brain damage. After exposure, merely removing the victims from the area is not enough. Some form of medical attention is required.