President Barack Obama has ordered U.S. flags in West Virginia to be flown at half-staff, according to The Associated Press. In a proclamation issued Monday, President Obama said all U.S. flags in the state are to be flown at half-staff until sunset on Sunday. The proclamation comes as federal and state mine safety officials begin their investigation into the nation’s worst coal-related mine accident in 40 years.

A miner’s helmet is placed amid the floral arrangements surrounding the casket of miner William Roosevelt Lynch of Oak Hill, W.Va. during funeral services on Sunday, April 11, 2010, in Beckley, W.Va. Lynch was one of 29 miners who died in the explosion at Massey Energy Co.’s Upper Big Branch mine in Montcoal, W. Va. on Monday. (AP Photo/Amy Sancetta)