Compliance with the Mine Act, MSHA officials added, continued to improve last year, with an 18% reduction in violations cited since 2010. And while the number of U.S. mines decreased slightly—to 14,093 in 2012 over 14,176 in 2011—the number of miners increased to 387,878 from 381,209 year-on-year.

Overall, 2012 fatality rates stood at 0.0110 deaths per 200,000 man hours. Reported injuries, on the other hand, were 2.56 per 200,000 hour worked. Each reduction, added MSHA, beat record historical lows in 2011.

MSHA-issued citations and orders, meanwhile, fell to 139,770 in 2012 from 156,802 in 2011—an 11% decrease. Penalty assessments dropped last year to $120.5 million in 2012 from $160.8 million year-on-year.

Altogether, 20 coal miners died in on-the-job accidents in 2012—the second-lowest number ever, with a fatality rate at 0.0159 deaths per 200,000 hours worked, also the second-lowest ever recorded. Reported injuries were 3.16 per 200,000 hours worked, also the lowest ever. Citations and orders issued declined, too, falling to 79,250 in 2012, from 2011’s 93,330—a 15% reduction.

The coal industry saw decreases in the number of mines—to 1,871 from 1,973—and in production—to 1,018 million tons from 1,095—between 2011 and 2012. While the number of coal miners also decreased from a decades-long high of 143,437 in 2011 to 137,650 in 2012, it was the second-highest decrease for any year since 1994.