The Hawaii Occupational Safety and Health Advisory Committee began an investigation Thursday of the accident that killed one worker and critically injured another Wednesday morning at a Hawaii island thrill ride.

An inspector with the state Labor Department’s HIOSH spent most of Thursday at the accident site at Paukaa, north of Hilo, with John White, president of Experiential Resources Inc., the company that built the zipline course for Gary Marrow’s Lava Hotline LLC.

White said he does not know what caused one of the two towers holding one of the eight ziplines to topple, and is working closely with the agency to find answers.

Hawaii County police identified the man killed as Ted Callaway, 36, of Maui. Callaway had traveled halfway across a 2,300-foot-long wire-rope cable when the tower supporting the line fell. He plummeted 200 feet into a dry riverbed.

Police said his co-worker, Curtis Wright, 43, of Ohio, remains in critical condition. Wright, who was on the tower, fell 30 feet.

White said Wright was transferred to an Oahu hospital, and his mother flew to Hawaii from the mainland to be him.

White said Experiential had completed the construction of the course, and Marrow’s company had tested the line and requested an adjustment to only the line involved in the accident. White did not know whether customers had used it, which is an issue because police said customers had complained about its slow speed, which prompted the adjustment.

"We do multiple tests from weighted backpacks," he said. "Nonhuman things all did fine over the two weeks."

One man was on the sending tower, the other on the receiving tower, with one on the line. The uninjured worker made the call for help, White said.

Experiential has built four other ziplines in Hawaii — three on Maui and one on Kauai — and more than 1,000 zipline spans in 40 states and 12 countries, without a single other fatality or tower collapse, White said.

"We are scratching our heads with what happened here," he said.

Labor Department spokesman Bill Kunstman said because the investigation involves a fatality, the site is treated "like a crime scene," and HIOSH will confiscate equipment to protect the integrity of the scene, pull police and autopsy reports, consult with federal workplace safety officers and will likely hire a consultant to test equipment and check for manufacturer’s recommendations and any kind of national standards.

The investigation might take six months.

A quick scan of the Internet reveals more than 20 sites offering zipline rides on three islands, but the activity is relatively new and unregulated in Hawaii.

State Rep. Mark Nakashima, in whose district the incident occurred, said concern by his constituents about that particular zipline in conservation and agricultural districts caused him to look into zipline legislation.

When he found none, he introduced House Bill 1246 this year to expand a safety law with respect to amusement rides to cover ziplines.

It did not pass.