Federal investigators are preparing to release their latest findings about the Upper Big Branch mine explosion to the families of the 29 coal miners killed in the April 2010 tragedy in southern West Virginia.

Mine Safety and Health Administration spokeswoman Amy Louviere says the private meeting is scheduled for Tuesday evening at the agency's academy in Beaver. A public briefing is set for Wednesday.

MSHA is still investigating, but officials believe the explosion started with a small methane gas ignition fueled by coal dust. An independent investigation commissioned by former Gov. Joe Manchin reached the same conclusion last month.

Investigators have rejected former owner Massey Energy's theory that an uncontrollable flood of methane overwhelmed safety systems.

The explosion was the deadliest at a U.S. coal mine since 1970.