Beginning on September 23, 2017, the Occupational Safety and Health Administration (OSHA) will significantly reduce the Permissible Exposure Limit (PEL) for respirable crystalline silica during work at construction projects from 250 to 50 µg/m3 (micrograms of silica per cubic meter of air), averaged over an eight-hour day. This new PEL applies to all occupational exposures to respirable silica in construction work, except where employee exposure will remain below 25 µg/m3