It was quiet chaos Friday as firefighters, police, ambulance crews and staff of local mental health care facilities faced a fictional worst-case scenario: a bomb exploding at Acadia Hospital in Bangor.

While everything seemed normal outside, the make-believe explosion inside set the Acadia Hospital on fire, injured staff and dozens of patients and set into motion procedures for containing damage and treating the injured.

It’s a new twist on emergency preparedness drills that previously involved downed planes or hazardous spills. Thrown into the trauma mix of victims suffering varying degrees of injuries were patients with pre-existing mental health conditions.

Among them was a man who had killed his best friend and the friend’s wife who was hospitalized for depression and homicidal tendencies toward her husband’s killer.

Volunteers playing the victims were given symptoms, anxieties and psychoses and told to play their parts, affording emergency personnel a glimpse into what they might have to deal with should the need arise.

Those that could walk and weren’t injured were the first to evacuate the building, while the bomb squad from the Bangor Police Department was called in to diffuse a second bomb. In the scenario, the first bomb had been set off by a hospital staff member who had been searching the building for the bombs.

Once the bombs were defused, the Fire Department took over control of the mock incident, those injured were taken away by one of several waiting ambulances.

Those who were not injured, and those whose injuries weren’t so serious, were taken to Bangor Mental Health Institute, where the G3 wing has been set up precisely for such situations: temporarily housing patients on short notice, said Chip Fussell, chief operating officer for BMHI.

Throughout their transition, the patients were assessed for medical injuries, as well as for mental health concerns. It was at BMHI that patients such as the homicidal widow were isolated and given one-on-one attention, said Bob Magaw, clinical nurse manager for BMHI. Others lingered in small groups, some petting dogs that brought in for the emergency. Part of the Therapy Dogs International, an organization that provides animal companionship to the elderly and the infirm, the five Disaster Stress Relief dogs provided a valuable service during the crisis.

Eunice Phillips of Hancock brought her schnauzer, Kipper, to the drill. “It’s a amazing what these dogs can do,” Phillips said.

For organizers of the mock disaster, the event provided insight, while glitches turned into lessons.

Emergency personnel first set up a command center on Stillwater Avenue, originally scheduled for behind the hospital. At BMHI, a radio used by personnel relaying information went dead during the drill.

Organizers will continue studying the drill results.

“There is no such thing as a bad drill because we always learn so much from [them],” said Kathy Knight, director of Emergency Preparedness for Eastern Maine Healthcare, the parent company of Acadia Hospital.