The owner of the Upper Big Branch coal mine in West Virginia, where 29 men died in an explosion last year, has agreed to pay $209 million in civil and criminal penalties and promised to make major safety improvements to its mines, federal prosecutors announced Tuesday.

The deal between the federal government and Alpha Natural Resources, which acquired the Upper Big Branch coal field when it bought out Massey Energy in June, is the largest settlement in a criminal investigation of a mine disaster in U.S. history, the U.S. attorney’s office said.

Alpha has agreed to pay $46.5 million in restitution to the families of those who died — plus two co-workers who survived the accident — $1.5 million per family. The company will spend $80 million to boost safety in all of its underground mines and set up a $48 million fund for mining-safety and health research. Alpha Natural Resources also agreed to pay $34.8 million in fines and fees that Massey Energy owed to the Mine Safety and Health Administration.

“Collectively, these requirements will set a new standard for what can and should be done to protect miners,” U.S. Attorney Booth Goodwin said at a press conference Tuesday announcing the settlement. “My hope is Alpha’s adoption of the measures contained in this resolution will give the rest of the industry a strong push to follow suit.”

Before Tuesday, the largest penalty ever paid by a mining company had come in 2008, when Massey Energy agreed to pay $4.2 million in fines for a fire at the Aracoma Alma mine in West Virginia that trapped 12 miners and killed two. The company had admitted to knowingly violating mandatory safety standards in that accident.

Federal officials noted that Tuesday’s deal addresses only corporate criminal liability for Alpha Natural Resources and Massey. The investigation is ongoing, and other individuals, including those at Massey Energy, could still face prosecution, the officials said.

As part of the safety measures, Alpha has pledged to install monitoring equipment at its underground mines to ensure that they are free of explosive methane gas and combustible coal dust. The company will also build a training facility and create a new safety curriculum for all of its miners.

Later on Tuesday, the Mine Safety and Health Administration is expected to announce the results of its investigation into the Upper Big Branch disaster.

In March, an earlier independent team appointed by former West Virginia governor Joe Manchin had concluded that the mining disaster could have been avoided if Massey had followed safety standards. That report had criticized MSHA for failing to intervene at the Upper Big Branch mine even after it had been issued 515 citations for safety violations in 2009.

“There should never be another [Upper Big Branch], and this announcement is aimed squarely at that goal,” Goodwin said. “For far too long, we’ve accepted the idea that catastrophic accidents are an inherent risk of being a coal miner. It’s long past time we put that myth to rest. We believe that this agreement does that.”