Regional OSHA Director Richard Tapio said the field investigator could be at the Western Gas Resources natural gas-processing plant two to three days.

"It all depends on what the investigator starts to observe. But normally we're there a couple of days," Tapio said.

The explosion occurred last Friday with enough fire and force to injure three plant employees and shake books off shelves in homes in the vicinity of Midkiff, located in Midland County, about two miles west of the plant, emergency responders said at the time.

The agency will first focus its investigation on the accident itself and the cause, Tapio said.

As part of the probe, the OSHA investigator will take samples and conduct tests at the explosion site and interview witnesses, Tapio said.

Plant manager Bryant Hazard said more information on the incident would not be available until today at the earliest.

At the time of the accident, Midland County Sheriff Gary Painter attributed it to "some kind of problem internally with some of the equipment." "There was an explosion of gas that had collected," Painter said.

Tapio said he didn't hear about the incident until this weekend and only got the case Monday afternoon.

"I got it from an online news service," Tapio said. "I didn't even know about it." OSHA only requires employers to immediately report accidents if they result in a fatality or five or more injuries, Tapio said.

However, even if he had known about the accident earlier. Tapio would have been pressed to find a field agent to send to the plant before Tuesday.

All 11 of the regional OSHA investigators were gathering information on a spate of deadly accidents.

Three construction workers in Amarillo were killed recently, and an oilfield worker was killed this past weekend when a piece of equipment fell on him at a well site in Rankin, Tapio said. An OSHA investigator was investigating that accident on Tuesday, he said.