Determination of unsafe levels of carbon monoxide is different for each person. Since carbon monoxide is a poison, it affects everyone at different levels. Age, size, and health are other factors that can determine the effect CO has on them. You should contact your own physician for advice regarding the issues of safe carbon monoxide levels. Everyone is at risk at some level from carbon monoxide poisoning, but some people are more vulnerable than others. Unborn babies, infants, children, seniors, and people with heart or lung problems may be at higher risk from carbon monoxide poisoning for a variety of reasons. Be sure to install carbon monoxide detectors for protection against unsafe levels of carbon monoxide.