Nearly a month after an explosion in the basement of landlord Jamison Inc.’s 20-story office tower at 811 Wilshire Blvd., the building is finally open.

City officials late last week gave roughly 550 workers the greenlight to enter the 337,100-square-foot Class A office building for the first time since the Aug. 20 explosion. Takami, the 11,000-square-foot Japanese restaurant on the building’s penthouse level, is not yet up and running, but will reopen its doors Thursday.

The explosion damaged the basement and parts of the ground floor of the building, according to representatives of Jamison and the Los Angeles Department of Building and Safety. It took a month to restore the building’s fire sprinkler system and plumbing system, and to repair the basement walls, elevators and elevator shafts, representatives said.The damaged elevator shaft was especially to blame for the holdup.

“For the most part, the fact that the elevators were out of service, that’s what prevented occupants from reentering until last week,” said David Lara, assistant bureau chief at the building and safety department.

“The owners had been working 24/7 from the moment the building lost its power to get everything up and running to the satisfaction of the Fire Department and the Department of Building and Safety,” a Jamison representative said.

The cause of the blast is still under investigation. It is believed to have involved a Los Angeles Department of Water and Power electrical vault, but the exact reason for the explosion is unknown.

Jamison offered all tenants free office space at its numerous downtown office towers during the month the building was closed, according to a spokesperson for the firm. Those office buildings included Jamison’s California Market Center at 110 E. Ninth St. The spokesperson declined to comment on how much the damage and closure cost the firm.

Takami’s owner, Emil Eyvazoff, was more vocal about his losses during the month his restaurant was closed. Including the loss of revenue from the 34-day closure and the loss of spoiled foods and fine wines, he estimates the damage amounted to more than $800,000.

Eyvazoff continued to pay his 105 employees during the closure, which cost him and his partners more than $200,000. The insurance fronted some pre-payment but nowhere near the total number, he said. Now, employees are busy preparing for the restaurant’s reopening tomorrow.

“Half of the staff have been working long hours since Saturday cleaning and preparing for Thursday, which is almost like a reopening,” he said. “The other half is a street team handing out flyers to let people know what happened to us.”