If confirmed as U.S. labor secretary, will Alexander Acosta enforce OSHA’s already-in-effect silica rule? Or will the Trump nominee follow the president’s anti-regulatory agenda and nullify the regulation?

No one knows. Under intense questioning during Senate confirmation hearings, Acosta declined to answer a number of questions regarding worker safety, leaving advocacy groups and some politicians frustrated.

In one testy exchange, Sen. Elizabeth Warren (D-Mass.) tried to elicit a response from Acosta about whether or not he would enforce the rule issued during the Obama administration that limits the amount of respirable silica dust that workers can legally be exposed to.

When inhaled, silica dust particles can penetrate deep into the lungs and cause disabling and sometimes fatal lung diseases, including silicosis and lung cancer, as well as kidney disease.

“You want to be secretary of labor and you’re telling me, evidently, that you have no opinion on whether or not high on your list of priorities would be to protect a rule that keeps people from being poisoned,” said Warren.

“Senator, high on the list of priorities will be to protect the safety of workers with appropriate rules,” Acosta answered.

OSHA estimates that more than 2.3 million workers in the United States are potentially exposed to dust containing crystalline silica with nearly 90% of those workers employed in the construction industry.

The agency estimates that the silica rule – which was four decades in the making -- will save more than 600 lives and prevent more than 900 new cases of silicosis each year, along with provide net benefits of about $7.7 billion, annually.

President Trump has announced plans to eliminate at least 75 percent of the existing federal regulations, leading safety advocates to wonder if the silica rule will be one of them.

“The president has directed each cabinet officer to review all rules,” Acosta said during the hearing. “I cannot make a commitment because the Labor Department has an order to review all rules.”

Warren accused Acosta of “hiding behind an executive order” issued by Trump.