Federal authorities are investigating the death of a worker killed at Denver International Airport this morning when he was hit by a giant machine scrubbing aircraft tire marks from a closed runway.

The worker, employed by a subcontractor, was hit at 5:16 a.m. by the massive orange runway sweeper during a routine maintenance operation on runway 16L/34R, DIA spokesman Chuck Cannon said.

The big sweeper was driven by a DIA maintenance worker.

Denver Police Detective John White said the worker apparently bent over to pick up an object, and was unable to be seen by the sweeper operator.

The name of the victim, believed to be in his mid-40s, has not been released.

The subcontractor, Rampart Hydro Services, uses big trucks blasting high-pressure water to strip rubber residue left by landing jetliners from runways.

Cannon said it was unclear why the accident victim was on foot.

"That will certainly be part of the investigation," he said.

It wasn't immediately clear whether the predawn darkness contributed to the accident. The cleaning crew had been working overnight, when air traffic drops off.

The DIA sweeper driver will be interviewed by federal safety investigators. Denver police are assisting in the accident investigation.

The DIA sweeper driver and a second Rampart Hydro worker who was at the scene have been offered counseling services, Cannon said.

Herb Gibson, Denver area director for the Occupational Safety and Health Administration, said he couldn't recall any other runway deaths at the airport.

The last worker death occurred in January 2005 when a United Airlines employee died after a jet extinguisher exploded in a hangar, he said.

The runway remained closed this afternoon, but air traffic wasn't affected because DIA diverted flights to five other runways, Cannon said.

The runway will be shut down "as long as the investigation needs it to be closed," he added.

The worker's employer, Rampart Hydro Services, based in Coraopolis, Pa., did not have an immediate comment on the death this morning.

The firm has the largest U.S. fleet of "ultra-high pressure" spraying vehicles, according to the company Web site. The "Runway Blaster" truck can clean runways at rates exceeding 20,000 square feet per hour.

The death comes less than a week after an electrician drove on a DIA runway without authorization.

DIA restricted motor vehicle access to the airfield and increased driver training after that violation. No aircraft were in the area where the motorist crossed the runway, officials said.

The Associated Press contributed to this story. gathrighta@RockyMountainNews.com

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