NEW CASTLE — Inmates rioted for two hours at a prison here Tuesday afternoon, resulting in two injured staff members and eight injuries reported among inmates. None of the injuries was considered life-threatening.

An ongoing investigation will determine what motivated the riot.

Department of Correction Commissioner J. David Donahue said staff at the privately run prison followed protocol by acting cautiously during the standoff and that no one escaped during the disturbance.

“You don’t run into a burning building unless you understand what the parameters are,” Donahue said, at a news conference in the prison’s parking lot.

This came a month after Arizona hired Indiana to keep up to 1,260 Arizona inmates here. About 630 Arizona prisoners were transferred here to date, adding to the 1,000 from Indiana.

The riot began when about 40 Arizona inmates, housed separately from those from Indiana, refused to return to their cell block after leaving the cafeteria.

“For some compelling reason, they decided not to return in a routine fashion,” Donahue said. Some of these inmates removed their shirts in a show of defiance to guards.

About 100 Indiana inmates who observed the incident from the other side of a fence in the recreation yard began rioting. Fires were set, and inmates brandished improvised weapons until the disturbance ended.

Seven had minor injuries, including five from tear gas that guards used to subdue rioters, said Trina Randall, a spokeswoman for GEO Group Inc., the Florida-based company managing the prison.

Authorities withheld the condition of the two injured staff members. One was knocked down by inmates in the courtyard. Donahue said he did not know how the other was injured. Neither was seriously hurt, he said, and all other prison staff was accounted for.

Windows were broken out, and small fires caused some superficial damage, but no significant structural damage occurred, according to the commissioner.

Donahue said that answers to questions about what motivated the Arizona inmates to act out in the first place are pending an ongoing investigation in which guards, inmates and other staff members at the prison will be interviewed.

Indiana State Police Sgt. Rod Russell said that, because inmates are housed separately, the riot shouldn’t be considered a direct conflict between the inmates from different states.

Donahue said reports that Arizona inmates were being treated unfairly were unfounded, and that standard procedure dictates that inmates receive an equal share of services available at whatever facility they are detained.

The commissioner said differences in Indiana’s prison system and Arizona’s may have caused some unrest among the Arizona contingent, but did not offer any specific details.