Part of Stillwater prison remained on lockdown Thursday after an inmate attacked two employees without warning, sending both to the hospital.

The inmate had approached a female correctional officer and a contract food service employee with a complaint and then suddenly began beating them in the prison's dining hall about midday Wednesday, said John Schadl, a spokesman for the Minnesota Department of Corrections (DOC).

Additional officers raced to the scene and the offender was subdued, Schadl said.

"This incident underscores how dangerous this work can be," said Corrections Commissioner Tom Roy. "We have been working very hard to make sure that our staff has the training and the tools they need to respond when incidents like this occur."

The number of offender-on-staff assaults in Minnesota's 10 prisons has dropped sharply over the past two years, Roy said. In 2010, there were 42 such incidents. In 2011 there were 16, and in 2012 there were 17, he said.

"We would not dispute that," said Jennifer Mundt, spokeswoman for the American Federation of State, County and Municipal Employees (AFSCME), the union representing most of Minnesota's correctional officers. "We would still argue that some prisons are understaffed. The inmates are keenly aware of that and they push for control of their prisons."

Recently, the Department of Corrections started a new training program for employees who work with offenders on a daily basis, called Crisis Intervention Training. The program addresses the challenges of working with offenders who have mental health problems and helps staff recognize and defuse potentially violent situations before use of force is needed.

"This training won't stop every assault, but it can help us reduce the need to use force," Roy said. "We are committed to making the workplace as safe as we can for our staff."

Mundt said the union agrees with the training and believes it will reduce the frequency of injuries to officers and other prison employees.

Schadl wouldn't talk about details of Wednesday's assault because the DOC's Office of Special Investigations is investigating the incident. When that's concluded, Washington County Attorney Pete Orput will decide if criminal charges should be filed, he said.

In June 2010, a major disturbance in a housing unit at Stillwater prison occurred when an inmate attacked another with a homemade knife, inflicting facial injuries. All 280 inmates in the B West cellhouse were put into lockdown.

Stillwater prison, with more than 1,600 offenders, houses a high percentage of Minnesota's most violent criminals, including more than 400 murderers and about 600 others convicted of aggravated assault, rape and robbery.

Kevin Giles • 651-925-5037 Twitter: @stribgiles