It's when it is removed from a building that the fibers can scatter and be inhaled. Being in a room with asbestos in the ceilings, for example, is not dangerous, if the asbestos is well contained in the ceiling. Coal tar fumes are also very dangerous. We know that miners who mined coal and smoked have very high risks of developing lung cancer. Other risk factors for lung cancer include exposure to nickel, chromium, arsenic, radiation and radon.
Radon is a natural radioactive gas emitted from the earth.
It is not a significant problem in California. In fact, it's quite rare. But, in pockets of the Northeast, there can be a steady production and excretion of radon into people's basements. This is often tested for in these areas. Since radon is not present in all areas of the country, not everybody should go out and test their home.