HONG KONG — Dozens of Chinese schoolchildren have been hospitalized after being accidentally poisoned in the classroom by a UV light. Again.

Authorities in the city of Tianjin say 44 first-graders were exposed to up to nine hours of UV after school staff forgot to turn off a disinfection lamp in their classroom, leaving most of the students with damage to their eyes and face and some with serious burns.

Chinese schools use UV lights to disinfect classrooms and kill germs but the lights are only meant to be used when there are no children in the room or for very short periods of time. Prolonged exposure to UV light can be very harmful, especially to exposed skin.

The story surfaced this week after parents at the Dagang English Experimental Primary School in Tianjin found their kids after class complaining about sore eyes and vomiting. Medical checkups soon revealed the cause.

Parents uploaded pictures of their children with bandaged faces — as well as videos of their furious confrontations with school officials while stunned police looked on. The scandal quickly took over the national conversation online and was even picked up in staid Communist Party newspapers and state TV newscasts.

In a video produced by Pear, a Chinese video service, a parent spoke angrily about the school dodging responsibility.

“Their eyes are hurting and their eyelids are really sore,” a parent says in the video. “But it’s not just the eyes. Because their exposure to UV is too much, what about the long-term effects?”

The story touched a nerve with the Chinese public partly because it’s a nightmare scenario for parents that has played out over and over across the country in recent years, from Changchun city in northeastern China to Shenzhen, in the south. In September, students in eastern China’s Jiangsu province suffered peeling skin and blurry vision in an eerily similar incident. In the city of Guangzhou in 2016, the same thing happened at two different schools in the span of three days, injuring 23 fifth-graders on one campus and 80 in the other.

“This has happened so many times,” said a top-rated comment on Weibo. “I suggest engineers build a buzzer for UV lights.”

Local authorities in Tianjin’s Binhai district — the site of a deadly chemical explosion three years ago that killed more than 170 — ordered an investigation and dispatched psychological counselors to visit affected children at home.

From food safety doubts to kidnapping scams, Chinese parents perennially complain about the stress of raising kids in a country with lax regulations and occasionally shocking crime. But parents have been particularly on edge this year, after a fake vaccine scandal took down one of the country’s leading pharmaceutical firms and allegations of child abuse at an expensive, U.S.-listed kindergarten chain exploded on social media.