The U.S. attorney's office said in a news release that Tyson Foods pleaded guilty to a "willful violation of an Occupational Safety and Health Administration standard resulting in the death of an employee," the most serious offense available to the federal agency. Tyson Food has agreed to pay $500,000, the maximum criminal fine, and also will serve one year probation.

The plea stemmed from the Oct. 10, 2003, death of Jason Kelley, a maintenance employee at Tyson's River Valley Animal Foods facility in Texarkana.

Federal authorities said even though the company had made improvements at other plants following a 2002 worker death, Tyson failed to take steps to prevent Kelley and others at the Texarkana plant from being exposed to toxic hydrogen sulfide gas produced by the use of high-pressure steam processors called hydrolyzers to convert poultry feathers into meal.

Another employee and two emergency responders were hospitalized due to exposure while trying to rescue Kelley.