The death toll from a fire at a Beijing hospital rose to 29, including 26 patients, authorities said Wednesday, and a dozen people had been detained including the hospital’s head and her deputy.

The fire broke out at the private Changfeng Hospital on Tuesday afternoon and forced dozens of people to evacuate. Some who were trapped had to escape from windows using bedsheets tied together.

A nurse, a medical assistant and a family member also died in the incident, said Li Zongrong, deputy head of Fengtai district.

The cause of the fire is under investigation but officials say they believe it originated from welding sparks from work being done in the hospital’s inpatient wing. Among the 12 people who were detained was the head of the construction crew.

A total of 39 people are being treated for injuries, three of them in critical condition, officials said. Rescue crews and medical staff from around the city were mobilized, with squads plucking some of the 142 people who were evacuated from air conditioning units on the building’s exterior.

Safety rules are frequently ignored in China, but accidents on the level of the Changfeng fire are treated with a much higher level of scrutiny. Construction accidents sometimes result from corners being cut on work hours and safety conditions, while local officials are bribed to ignore violations.

The central government has pledged stronger safety measures since an explosion in 2015 at a chemical warehouse in the northern port city of Tianjin killed 173 people, most of them firefighters and police officers.

(AP)