Many safety standards passed by Congress in the wake of the explosion at the Sago Mine still aren't in place two years after the accident.
Congress overhauled mine safety rules after the January 2, 2006 blast that killed 12 men in West Virginia.
But the federal Mine Safety and Health Administration has yet to implement some of the standards established by the laws. The United Mine Workers union, which represents some of the 42,000 miners who work in the nation's 670 underground coal mines, blames the agency and mine owners for the delays.
MSHA also hasn't established standards mandating stronger methods of sealing abandoned sections of underground mines.
The agency's director says progress has been made in implementing the new standards, despite facing a shortage of trained mine inspectors and other difficulties.