One worker was severely burned and another slightly injured Thursday evening as flames swept the wooden scaffolding at the construction site of Phase 11 of Holyoke Center.

Cambridge Deputy Fire Chief William Cremins estimated damage to the building at $10,000. A spokesman for the builders, the Wexler Construction Co., said that it could not be immediately determined how long the fire would delay work.

The fire broke out about 5:50 p.m. on the fourth story of the unfinished building and quickly spread to the other four floors. The injured worker--Eli Lorbin, 51--was trapped by the flames and critically burned before firemen carried him to safety. He is on the danger list at Masachusetts General Hospital, where his condition was described yesterday as poor.

A second workman, Joseph R. Correnti, was treated for smoke inhalation at Cambridge City Hospital and released.

Two alarms were sounded and 17 places of fire fighting equipment were called to fight the fire. It took them about 30 minutes to bring it under control.

Heating Salamander

Cremins said Saturday that the blaze may have been caused by a propane-gasheating salamander, a device used for drying freshly poured concrete. The State Fire Marshal's Office is investigating the fire.

According to Dana L. Farnsworth, director of the University Health Services, the fire posed no serious threat to Phase I of the building. The staff at Stillman Infirmary was prepared to evacuate 100 patients if necessary, he said.

patients if it became necessary, he said, but there was never any real danger.