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 100 underground mines have closed in West Virginia and Kentucky over the last five years as the energy industry has moved away from Appalachian coal.

The U.S. Mine Safety and Health Administration also credits its revamped approach to inspections. After Upper Big Branch, MSHA began sending teams of inspectors to target problem mines, many of them underground operations in West Virginia and Kentucky, which are still home to nearly half of the nation’s coal mines. Federal inspectors have written nearly 14,000 citations during those visits, called impact inspections.

MSHA chief Joe Main has said the increased enforcement has reduced serious violations that could lead to injury or death by about 60 percent in mines that MSHA has kept a close watch over since 2010.

Yet some mines consistently fail to follow rules meant to curb explosion risks, including some owned by the company that took over Massey’s operations.

In January, federal officials found excess methane and coal dust at Mill Branch Coal Corp.’s Osaka mine in Wise County, Va. The mine is owned by Alpha Natural Resources, which bought Massey’s mines in 2011. During the visit, inspectors pulled miners out of two working sections, temporarily shutting down production. The January visit to Osaka was the fifth impact inspection at the mine.

At another Wise County mine in November, inspectors found 2-foot deep accumulations of combustible materials and coal dust in working areas of Regent Allied Carbon Energy’s No. 2 mine. MSHA ordered the belt lines shut down since the mine had not followed an approved ventilation plan, and officials noted that the water supply to sprayers that suppress coal dust were not turned on.