Two construction workers burned in this week's downtown San Diego hotel explosion have undergone temporary skin graft surgeries and a third worker could get skin grafts on Friday.

The two workers who underwent surgery Wednesday at University of California, San Diego, Medical Center will remain in drug-induced comas for two weeks to control pain.

• Click here for photos of the blast-damaged hotel

A third worker is too swollen for skin grafts and surgery for that worker could be scheduled as early as Friday.

Medical center burn unit chief Dr. Bruce Potenza says the men may be ready for permanent skin grafts late next week.

All three are in critical condition.

Thirteen workers were injured during Monday afternoon's explosion at the San Diego Bayfront Hilton, a 30-story hotel under construction. Fire investigators say a water heater flame or electrical spark ignited natural gas that had been leaking into a mechanical room on the fifth floor.