Two Hogle Zoo animal keepers were injured, one critically, when they were attacked Saturday by chimpanzees that escaped their primary enclosure and accessed the employee service area in the Great Apes Building.

Jamie Bradley, 28, Centerville, was upgraded from critical to fair condition following surgery at University Hospital, and Kimberly Tropea, 35, Salt Lake City, was treated and released.Bradley sustained extensive head, arm and leg lacerations, while Tropea suffered arm lacerations, said hospital spokesman John Dwan.

Two of the chimpanzees (an adult chimp weighs 150 to 200 pounds and stands 3 1/2 to 4 feet in height) were shot when they became dangerously aggressive during the attack. The two animals were euthanized because of the severity of their injuries, zoo officials said.

Zookeepers were able to safely contain a third chimpanzee and remove it from the area where the attack occurred, zoo Executive Director Craig Dinsmore said.

Emergency procedures were put into place as soon as staff became aware of the situation, and about 12 zoo employees rushed to the Great Apes Building, Dinsmore said.

Visitors on zoo grounds were escorted inside buildings until all animals were secured, he said. Dinsmore stressed that the animals never accessed public areas and that patrons were not at risk.

The incident occurred about 10:15 a.m., nearly an hour after the zoo opened, and was restricted to a service area. Salt Lake Fire Department paramedics, other emergency personnel and two ambulances were dispatched to the zoo at 10:24 a.m., said Capt. Devin Villa, department public information officer.

The zoo director said he did not know how the three chimpanzees got out of the area where they would normally be and into the service area where animals are moved and their food is prepared.

Back areas or areas where animals are off exhibit are locked in the Great Apes Building, said Cyndy Andrews, director of development and marketing.

Other animals, including one chimp (the one that was safely moved from the area of the attack), three gorillas and two orangutans were in the same building but were not in the area where the attack occurred, she said.

Dinsmore said one of the chimpanzees was "actively attacking one of the employees (Bradley) when another employee arrived on the scene with a shotgun."

The employee first yelled at the animal to try to stop the attack, then shot the chimp after it lunged at another employee.

"(Shooting an animal) is a very tough thing to do," Dinsmore said. "Obviously, he waited as long as he could, yelling at the animal trying to get it to stop before he took the shot."

Dinsmore added it is a "terribly, terribly difficult decision for a zoo employee to (shoot an animal) because we care about these animals."

Dinsmore said zoo officials would investigate the possibility of mechanical or equipment failure at the Great Apes Building, which has been in use more than 20 years.

"We have been over that building with a fine-tooth comb. We have not found any indication of a mechanical or physical breakdown," Dinsmore said.

Officials also will look into whether employee error could have been a factor in the incident, he said.

"We don't know, but we are certainly going to investigate that very, very thoroughly . . . You can build safety systems, but those systems require people to make the right decisions for them to be effective.

"Our hearts go out to the employees and their families. We are behind them. We want to do everything we can to take care of them, and we will investigate this incident very, very thoroughly to make sure we cover all the bases," Dinsmore said.

On Aug. 7, 1997, Hogle Zoo employee Robert Pratt was attacked in the same building by Tino, a 450-pound male Western lowland gorilla.

Pratt, who had worked at the zoo 33 years, suffered five puncture wounds on the upper part of his left arm and left torso and was knocked down. He was taken by ambulance to a hospital, treated in the emergency room and released from the hospital the same day.

A zoo news release issued after that incident said the attack occurred when Tino gained access to a basement holding area that Pratt was cleaning. Tino knocked Pratt to the ground and bit him. When the gorilla briefly entered a food preparation area, Pratt ran upstairs to notify staff.

Moments later, the animal returned to his holding area and was secured.

Pratt retired from the zoo last summer. Tino is still at the zoo, Andrews said.

Deseret News staff writer Spencer Young contributed to this story.