BECKLEY, West Virginia (AP) — Ex-coal company chief executive Don Blankenship pleaded not guilty Thursday to conspiracy and other charges in the deadliest U.S. mine accident in four decades.

It was the first court appearance for the former Massey Energy CEO since he was indicted last week. He is accused of ignoring safety and health regulations at the Upper Big Branch mine and lying to investigators about his company's safety practices. In April 2010, an explosion at the mine in Montcoal killed 29 men.

Blankenship, 64, could face up to 31 years in prison if convicted. His bond was not immediately set. The hearing was in a recess Thursday afternoon and his bond was expected once it resumed.

Wearing a navy blue pinstriped suit and red tie, Blankenship greeted the media when he walked into the courthouse and later entered the plea before the judge. He was released on a $5 million bond.

Family members of some of the men killed in the blast attended the hearing, but they, along with lawyers and investigators, are under a gag order not to talk to the media.

At Upper Big Branch, four investigations found worn and broken cutting equipment created a spark that ignited accumulations of coal dust and methane gas. Broken and clogged water sprayers then allowed what should have been a minor flare-up to become an inferno.

Blankenship has said natural gas in the mine, and not methane gas and excess coal dust, was at the root of the explosion. Authorities have dismissed the argument. He has also said if he goes to prison, it would be for political reasons.

The indictment painted Blankenship as a bullish micromanager who was intricately aware of Upper Big Branch's operations. At times, he received updates about the mine every 30 minutes, according to the indictment.

Massey was cited for safety violations 835 times from January 2008 until the 2010 explosion, the indictment said.