The world’s fastest-accelerating roller coaster in Japan has been suspended after several customers sustained bone fractures. Since December 2020, at least six riders were injured after riding “Do-Dodonpa” in Fuji-Q Highland Park. Four of the injured passengers said they had broke their neck or back, VICE World News quoted a park spokesperson as saying. The incidents from the roller coaster which operates at “super death” speed were reported to authorities on August 17.

Japanese newspaper Mainichi Shimbun reported that “four people have broken bones”. The bone-breaking injuries are the first since the Do-Dodonpa was built in 2001. Do-Dodonpa goes from 0 to 180 kilometers (or 112 miles) per hour in 1.56 seconds and the “air-launched” ride also features the globe’s largest loop, according to Newsweek.

Those injured were “in their 30s to 50s” and “broke bones including in their neck and back, with full recovery requiring between one and three months,” the Mainichi Shimbun reported.

In 2017, the top speed was raised from 172 to 180 kilometer per hour, but the modification didn’t cause any serious injuries, including bone fractures, until December.

No technical issues were found upon initial investigation, according to Fuji-Q Highland. The ride’s manufacturing company, Sansei Technologies, issued an apology but said it had no idea about what had caused the injuries.

Japan reported its last roller coaster-related death in 2007, when a roller coaster crashed into a guardrail as an axle on a car broke during a ride in Expoland in Osaka.

According to the International Association of Amusement Parks and Attractions (IAAPA), there is a one in 17 million chance of being seriously injured on a fixed-site ride in the United States.

Nihon University architecture professor Naoya Miyasato reckons the injuries could have been caused due to the coaster’s intense acceleration.

“If a rider can’t withstand the acceleration, then they sustain injury, which could be what’s happening here,” said Miyasato.