In a major ruling, a federal appeals court has rejected construction and other industries' challenges to a 2016 Occupational Safety and Health Administration rule toughening workers' exposure levels for silica dust, a substance that can cause lung cancer, silicosis and other respiratory illnesses.

In its decision, issued on Dec. 22, a three-judge panel of the U.S. Court of Appeals for the District of Columbia Circuit said OSHA had met legal requirements for, among other things, determining what standards are feasible, economically and technically. Leading the panel was Chief Judge Merrick Garland.

The OSHA rule reduces the exposure limit to 50 micrograms per cu meter for all industries, including construction. That standard is much more stringent than the previous level of 250 micrograms per cu m for construction and 100 micrograms per cu m for other industries.

The rule took effect on June 23, 2017, for the construction industry and one year later for the foundry industry. For the hydraulic-fracturing industry, the date was June 23, 2021.

OSHA began enforcing the construction silica standard on Sept. 23 but allowed a 30-day grace period for companies that were showing "good-faith" efforts to comply with the new rule.

Chris Cain, director of safety and health for North America's Building Trades Unions, called the court's decision "a huge win for the nation's construction workers and affirms that OSHA put out a strong, science-based standard."

The Associated General Contractors of America, which was among the groups that challenged the OSHA regulation, disagreed with the ruling.

AGC CEO Stephen Sandherr said, "It is disappointing that the appeals court has decided to allow the misguided federal silica rules to proceed despite the many legitimate concerns we and other groups raised about the measure."

Sandherr added, "Today's decision underscores just how difficult it is to overturn federal regulations, even one as deeply flawed as this measure. That is why we have long cautioned our members to take every possible step to comply with this measure instead of gambling on a long-shot legal victory."

Sandherr didn't raise the possibility of appealing to the U.S. Supreme Court, the opponents' last judicial recourse.

Brian Turmail, an AGC spokesman, said it is too early to determine whether there will be a further appeal.

Shortly after the decision was released, Turmail said via email, "We need to review the final ruling more thoroughly before evaluating any possible next legal steps."

The business groups contended that, among other issues, the regulation wasn't technically or economically feasible for the construction, foundry and hydraulic-fracturing industries.

For their part, unions contended that OSHA did not go far enough in a couple of areas. The court did direct OSHA to revisit its decision to omit provisions for "medical removal protections" for silica-exposed workers.