CHARLESTON, W.Va.  — The nation’s worst coal mine disaster in decades exposed lax safety measures at some Appalachian mines, issues that persist five years later despite the crackdown that followed, according to an Associated Press review of federal inspection records.

Excess methane gas and flammable coal dust fueled a fireball that raced through the Upper Big Branch mine in southern West Virginia on April 5, 2010, killing 29 men. The explosion and mass casualties rocked the mining community, which had just recorded its safest year ever in coal mines.

The revelation that inspectors repeatedly had cited the mine for buildups of coal dust and methane, with little disruption to the mine’s operations, drove calls for greater accountability. Federal authorities responded by stiffening safety rules, stepping up inspection raids and going after company higher-ups.

Prosecutors have won four convictions against former officials at Massey Energy, the company that owned Upper Big Branch, and secured a rare indictment on conspiracy charges against Don Blankenship, the former CEO. He has pleaded not guilty and is set for trial April 20.

In 2014, the nation again set a new low for coal mining deaths — 16 — in part because about a hundred underground mines have closed in West Virginia and Kentucky over the last five years as the energy industry has moved away from Appalachian coal.