In the coalfields of eastern Kentucky, it's known as the hoot owl shift. In those wee morning hours, while most people in this small eastern Kentucky town are sleeping, miners wearing hard hats, steel-toed boots and layers of black dust are still at work, deep underground.

Harlan County coalminer James Sargent stops by the Harlan County Coal Mine Memorial in downtown Harlan, Ky., on Friday, May 26, 2006, to show his respect to fallen miners. Sargent has worked in the coal mines for 25 years and is currently employed by A&M Mining Company in Pathfork. [AP]

With coal prices at record highs, mining companies have been pushing to increase production, adding overnight and weekend shifts and generating more overtime hours for miners who have some of the most physically grueling jobs in the country.

Industry groups and mine regulatory agencies are wondering if fatigue could be a common factor in the sharp increase in coal mining deaths this year. So far this year, 33 coal miners have been killed on the job in the United States, including 12 in January at the Sago mine in West Virginia and five on May 20 at Kentucky Darby No. 1. That's up from 22 coal miners killed throughout all of 2005, according the federal Mine Safety and Health Administration.

"It is something that needs to be looked at," said Bill Caylor, president of the Kentucky Coal Association. "If we're cranking out more production with the same number of employees, miners may be working six or seven days a week, instead of five, and potentially not getting enough rest."

Companies went in search of experienced miners about three years ago when prices for Appalachian coal skyrocketed. The region's coal is now selling for as much as $64 a ton on the spot market, a threefold increase in three years.

Coal operators have been pressing miners to keep up the pace.

In a memo to employees last fall, Massey Energy Chief Executive Officer Don Blankenship roused controversy by saying production is the top priority.

"If any of you have been asked by your group presidents, your supervisors, engineers or anyone else to do anything other than run coal ... you need to ignore them and run coal. This memo is necessary only because we seem not to understand that the coal pays the bills," Blankenship wrote.

A week later, Blankenship sent employees another memo, saying safety is the company's top priority.

The U.S. Energy Information Administration said Appalachian coal production has increased by 2 percent over the past year. Kentucky miners produced an additional 4 million tons over the period, raising the state's total to 120 million tons; West Virginia produced an additional 5 million tons, raising that state's total to nearly 156 million tons.

Kentucky's mining industry also has hired about 2,000 more miners over the past two years, raising its total to about 14,800, not counting managers, engineers and support workers, said Carlos Cracraft, a labor market analyst in the Kentucky Department for Workforce Development. West Virginia has added about 3,000 miners.

Cracraft said the miners, who earn an average $18.35 an hour, are working an average of 49.5 hours a week in Kentucky. That, he said, suggests that while some may have a typical 40-hour work week, others may be on the job for 60 hours or more.

The work is far from easy, said James Jarrett, 43, of DeBord in eastern Kentucky.

"I would say this is about one of the toughest jobs in the country," he said. "Ain't nobody else ever been where we've been, with a mountain over top of them. About every mine is working six days a week. I may get 60 to 70 hours a week, or I may go home in 48."

Still, most miners are glad to get the overtime pay, Jarrett said.

Joe Main, a mine safety consultant and former safety director for the United Mine Workers of America, said industry representatives and regulators should look at overtime when considering ways to improve safety.

Coal operators are so focused on the bottom line that they're using overtime instead of hiring additional workers, Main said.

Jane Rice Williams, chairwoman of the Kentucky Mining Board, said a shortage of miners could be one reason why miners are working so much overtime.

Chuck Wolfe, spokesman for the Kentucky Office of Mine Safety and Licensing, said he doesn't know if the five Harlan County miners killed by an explosion last weekend were on overtime. Company representatives didn't return calls seeking comment.

Main said he also is concerned about whether mine operators are providing enough safety training.

"I don't know what single factor is causing this rash of fatalities," Caylor said. "The only legitimate factor may be if miners are worked beyond the five-day week, that fatigue may come into play. Maybe it's too much overtime. ... When you sustain it, do it day in and day out, it does take a toll on you."