Federal regulators are proposing new safety rules that would result in speedier enforcement for mines that have shown a pattern of significant violations.

The proposal released Monday to eliminate warning letters is in response to a deadly explosion last spring that killed 29 men at the Upper Big Branch mine in West Virginia. It was the worst U.S. mining disaster in 40 years.

Federal investigators believe the blast was caused by a preventable buildup of methane gas mixing with coal dust, although Richmond-based Massey Energy Co. has disputed those findings.

Among other things, the rule proposals are intended to reduce delays caused by appeals that can last months or years.