Tomorrow, when the House Education and Labor Committee takes up the mine safety reform legislation, one major provision will be missing from the Democratic bill: Language to tighten to legal limit for coal dust that causes deadly black lung disease.

It’s a glaring omission, if for no other reason that it was a major part of the S-MINER Act, the legislation that Committee Chairman George Miller, D-Calif., and other reformers were pushing not so long ago.

Now, the new legislation — to be named in honor of the late Sen. Robert C. Byrd — does include important language to update the standards for “rock-dusting” to prevent coal-dust from contributing to underground coal-mine explosions.

I’m told lawmakers did not include the language to tighten the coal-dust limits because they expect MSHA to be issuing a rulemaking on this issue … well, yes — and no. MSHA does have a regulatory agenda item for reforming black lung protections.

MSHA has indeed sent a proposal to the White House for its approval as part of the agency’s “End Black Lung” initiative. But, the Obama administration and MSHA chief Joe Main have removed from that agenda Obama’s initial promise that the rule proposed by his administration would tighten the legal dust limit.

It’s also an 0dd explanation from Democratic lawmakers, given that their current bill does include language requiring MSHA to issue final regulations within two years “to provide coal miners with the maximum feasible protection from respirable dust, including coal and silica dust, that is achievable through environmental controls.”

As Coal Tattoo readers know, the National Institute for Occupational Safety and Health has recommended a tightening of the coal-dust limit since at least 1995. A Department of Labor advisory panel so recommended in 1996 … but today, Democrats in Congress have backed off putting those simple recommendations into law.