Our current chance of developing cancer sometime in our lives is 1 in 3. This risk is about one in 1000 to one in 100. They searched many data bases back to their origin in the 1970s and surveyed officials in the EPA, the FDA, Oak Ridge National Laboratory, and many other agencies. There was no written documentation, and no one could cite a source. The standard is not uniformly applied.
Perception is a major determinant as is dogma.
If a hospital's incinerator can't meet the standard, the waste would have to be trucked to a regional incinerator. Persons with active cavitary tuberculosis may fly on airliners and transmit their disease to flight attendants and fellow passengers. No one would dare ask a coughing passenger to wear a mask. But the penalties for disabling the lavatory smoke detector must perforce be announced before the airplane can depart from the gate. ETS gives the EPA and other eager do-gooders the pretext for ever more intrusive regulation of private behavior.