A woman technician was killed and four other persons were injured Friday afternoon when a violent explosion shattered a laboratory being used for Harvard Medical School research in Boston City Hospital's Thorndike Building.

Miss Urda Traenkee, a native of Germany who had recently come to Cambridge, was working near a heating oven in the lab when it exploded. She was killed instantly by glass fragments from the oven doors, hospital officials said.

Dr. Ralph S. Goldsmith, associate in Medicine, was injured by the flying glass. City Hospital surgeons performed an emergency skin graft operation on Dr. Goldsmith to replace flesh torn from his scalp. Goldsmith, who was conducting the lab's experiments in endocrinology, was released Saturday.

Cause Unknown

Three other technicians working in the lab suffered minor injuries, and were released from the hospital Friday night.

The explosion occurred at 3:15 p.m., when the workers had finished the day's experiments and were preparing to close the lab. Before they left, the oven exploded, sending glass fragments flying through the room and knocking two of the technicians to the floor.

Dr. George Curtis, Boston Medical Examiner, said last night that the cause of the explosion is still unknown. He sealed the devastated lab immediately after the explosion pending further investigation of the causes.

Friday's blast was the fourth major hospital explosion in Boston this month, and the second involving Harvard Medical School research. Two weeks ago two technicians were injured when an explosion ripped through a histology lab at the Med School.