Annette Morgan's forearms were badly burned. Drew Richardson inhaled some chemicals and was having trouble breathing. Barbara Gray had a fractured left rib. And Priscilla Eldridge was hysterical.

The automatic doors of the Arlington Hospital emergency room slid open, and stayed that way, as a stream of patients filled the room yesterday morning. Eldridge clung near the entry, staring.

"Oh my God, where's everybody else, where's everybody else?" she shrieked at the doctors. "You're not going fast enough. Take care of them! Take care of them!"

It was a test yesterday in Arlington Hospital; it was only a test. But for 60 frantic minutes, volunteers scribbled patients' names and nurses eased people onto stretchers and doctors decided in seconds whose injuries needed urgent care.

Arlington Hospital workers, who knew the drill was coming but didn't know exactly when, played the game to the hilt, partly because they have to; hospitals must stage full-scale disaster drills twice a year to maintain their stamp of approval from the nation's Joint Commission on Accreditation of Hospitals.

But the workers also played because they wanted to, because the drill stretches people and equipment to the brink of disaster, and leaves them on the safe side.

Yesterday's "catastrophe" also tested the Arlington Fire Department, which received a call at 10:26 a.m. of a chemical explosion at the Career Center, a clearinghouse for adult and vocational education and extracurricular courses.

The first firefighters on the scene found 24 "victims" -- students in the practical nursing and emergency medical training programs, elaborately made up to look burned, bruised, fractured or worse.

Paramedics set up a triage center on the Career Center's ground floor, assessing injuries to decide who needed immediate hospitalization, who could wait a while, who could not be saved. There was one "death" from cardiac arrest.

The hospital was called at 10:50 a.m. The first patient arrived nine minutes later. At 11, the public address system broadcast a "Code Yellow" -- the hospital's phrase for disaster.

Emergency room doctors and nurses huddled, listening to brief instructions from the head nurse and chief physician, then scattered.

Dr. Michael T. Rapp, chief of the emergency department, leaned briefly over Bernadette Buckley, 16, her face smeared with soot and her arms with fake blood. He then pinned a No. 2 triage tag -- yellow to indicate an intermediate level of urgency -- to her shirt.

Beth Lee, 23, lay on a stretcher, one hand fingering the large nail that protruded from her abdomen, through her flannel shirt. A red triage tag -- top priority -- dangled at her side.

Barbara Gray, 26, was having trouble breathing because of a fractured rib, and needed to sit up. "My problem is I don't know how to use the damn equipment," a nurse muttered, struggling to raise the back of Gray's stretcher.

Dr. Mitchell Heiman, chairman of the hospital's disaster committee, stood in the middle of the room and stared at the activity. "It is chaos, but hopefully it's organized chaos. You keep clearing it and clearing it, and eventually you get things quiet."

Heiman, along with the rest of the disaster committee, will evaluate yesterday's performance-under-pressure, looking for gaps in communication, lags in time, errors in paper work or treatment.

"The worst thing that can happen is that everything runs smoothly; then the drill would be a waste of time," he said. "We want to find out what's not working."

Heiman said the only glitch he noticed immediately was a delay by the fire department in notifying the hospital; emergency room staff had less than 10 minutes to prepare for the first patient.

Emergency department head nurse Diane Rickey said a real disaster prompts choices that are perhaps impossible to simulate.

"In the normal routine, you work as hard as you can to save somebody," said Rickey, whereas in a disaster, doctors and nurses must weigh injuries against resources, one person's chance of survival against another's.

"The old phrase is called 'playing God,' " Rickey said. "We don't have any real practice in doing that. There's no preparation for that kind of thing."