Asbestos fibers disbursed in the air are very small, and cannot be seen without magnification. As fiber concentrations build up in the air, however, their combined numbers begin to interfere with light transmission, and are then observed as a "haze" or "cloud" of dust.
The small size of asbestos fibers permits them to remain suspended in air for a long time. The settling rate of these fibers is so slow that it may take over 8 hours for one to settle 8 feet in still air. Air currents can carry asbestos fibers for great distances. These characteristics result in asbestos exposures to workers even after the creation of dust has ceased, and also at locations remote from the locations where fibers were released.
Once asbestos gets into the home on the clothing of a contaminated workman, it will remain indefinitely in the home. Asbestos gets into the rugs, carpets and gets re-suspended in the air by the family's movements and activities. Family members are then getting a 24 hour-a-day exposure to asbestos fibers, rather than a partial exposure during an eight-hour workday. Asbestos has no warning qualities. It does not irritate the skin, nose, eyes or mouth when inhaled. Asbestos cannot normally be seen in the air. Therefore, the members of the household could have substantial exposure to asbestos without knowing they are exposed. In addition, asbestos exposure at home adds to the exposure that a worker experiences during his 8 hours on the job such that he may well be said to have a full 24-hour exposure.
In 1955, Herbert Stokinger, recognizing that many substances had the potential to cause cancer, recommended in a presentation to a national symposium on threshold limit values for cancer-causing materials that the then current exposure level be reduced by a safety factor of between 100 and 500. Stokinger was a toxicologist with the U.S. Public Health Service. A copy of the September 1956 Industrial Hygiene Association Quarterly containing the prepared remarks of Dr. Stokinger delivered at the symposium of threshold limits at the 1955 Industrial Health Conference held in Buffalo, New York. At the symposium, Stokinger expressed his opinion that there were no safe exposure levels known to prevent cancer.