HONOLULU -- The Honolulu Zoo will undergo a review of all its safety procedures after a zookeeper accidentally left the gate to the orangutan exhibit open, city officials said.

It is the second time in six months that such an incident has happened at the zoo.

On Aug. 3, a zookeeper let orangutans Rusti and Violet into their exhibit, forgetting that he had left a gate to the exhibit open.

It happened at about 9:45 a.m. -- 15 minutes after the zoo opened to the public.

"I was very disappointed, because we've worked so hard to get our staff to be more aware of safety," City Enterprise Services Director Sid Quintal said.

The gate leads to a back access road, with Monsarrat Avenue just over the fence.

An alert groundskeeper saw Violet walking toward the open gate.

"(The groundskeeper) reacted in the most positive and heroic manner, yelled at Violet, got her to move back and then secured the gate and then notified the animal keeper of this near escape," Quintal said.

In early February, Berani the tiger walked out of his enclosure when another zookeeper mistakenly left two gates open. The zoo spent $50,000 on safety improvements and that zookeeper was disciplined.

"We have again reviewed what happened. Again, it was human error, and we have since implemented a new program, which is called 'time out,'" Quintal said.

Two days after the incident, the zoo put up signs in every exhibit that has potentially dangerous animals. The signs have a safety checklist for zookeepers.

Later this month, the zoo will hire a safety expert to review all their facilities and procedures.

"Maybe we're just too complacent to what's here. So, we want to get another set of eyes that will tell us, say, 'Hey, you need to look at this, you need to look at that,'" Quintal said.

The orangutan keeper was training another keeper when the incident happened, and that may have distracted him. He is on leave while the incident is being investigated and will most likely face some kind of discipline, city officials said.