The Occupational Safety and Health Administration sets limits for exposure to certain substances in the work place. One of them is crystalline silica. It's a common mineral found in lots of different building materials and it's known to cause cancer. Since 1971 the limit on how much workers could be exposed to during the course of an 8-hour shift has been set at 250 micrograms per cubic meter of air. New regulations set by OSHA have reduced that amount to 50 micrograms per cubic meter of air for workers in the construction industry and 100 micrograms for other industries.
The new regulations will go into effect in June, however employers have between 1 and 5 years to change their methods to fully comply with the new standards. Not surprisingly, employers in the affected fields fought against the new limits, insisting that such low levels of the dust could not be reliably maintained on most work sites. When inhaled over time, crystalline silica can cause lung damage and lung cancer. Limiting the amount circulating in the air with increased ventilation and protective gear is possible, but difficult.