Under the new rules, permitted exposures to silica throughout the construction and general industry would be cut to 50 micrograms per cubic meter of air over an eight-hour period from 100 micrograms under the old standard. OSHA is also now labeling silica a known human carcinogen, as it has been judged by IARC since 1996. This new rule may enable many developing countries to get much more serious about controlling silica dust levels in order to reduce the toll of silicosis, silicoTB, autoimmune diseases, and lung cancer.
This very important rule-making is long overdue and is based on a huge amount of published research.
There's also the piece at http://www.politico.com/agenda/story/2016/03/the-regulation-that-took-four-decades-to-finalize-000078.
I shake my head about the arguments opposing this inadequate standard. Canadian jurisdictions have been using 25 for a while, and CAN measure it. British Columbia's substitution regulation requires that carcinogens be replaced where possible. Furthermore, BC's construction companies requested improved protections for workers (see http://www.worksafebc.com/regulation_and_policy/public_hearings/assets/pdf/2014ProposedAmendments/Part6.pdf).
NPR and NYTimes report that OSHA/DoL releases the new silica dust standard: