Alex Hummell says few dentists seem worried enough about invisible, odorless mercury to take the kinds of precautions needed to prevent everyday exposures. As the head of a ... firm that sells sophisticated equipment to gauge airborne levels of highly toxic mercury at industrial sites worldwide, Hummell has watched manufacturers of all sorts put their employees through strict training programs in which they don special equipment to avoid even tiny exposures. Then he walks into dental clinics and is dumbfounded. On numerous occasions, he said, he has detected mercury levels in dental offices that were two to three times the average workday exposure limit of 100 micrograms per cubic meter set by the Occupational Safety and Health Administration, but patients and the staff were wearing little or no protective equipment. I've seen in dental offices what would make these other offices have to shut down," said Hummell. "They would be closing their doors and getting respirators on." Instead, he said, "there are kids running around everywhere. It's nuts. It's the exact same toxin, and it's being treated totally differently." Several years ago, Hummell said, he set up a booth at a regional dental conference in Denver to demonstrate how his equipment could pick up rising mercury levels with a mere gentle brushing of a filling in an old tooth.