''You reach this point that you just don't care about you,'' said Mr. Lopez, who is now 45. ''And you set your mind on work. And that's what they want. And that's how people get hurt.''

On March 2, 2002, it happened to him. He was working on some machinery, stretching awkwardly in a tight space, when he slipped and fell. His back slammed into metal. He heard a snap, he said, and felt dizzying waves of pain and nausea. In the dispensary, records show, he was pale and weeping and showing signs of shock. He said his pain -- a ''burning in the bone'' -- was so intense that it was a challenge just to breathe.

Had he been sent to a hospital, had an X-ray been done, it would have been clear that Mr. Lopez had suffered a terrible injury, a severe compression fracture in his spine.

But he was not sent to a hospital. ''They just tell me to sit down and wait for the safety man,'' he recalled. Ms. Sankowsky, in the dispensary that day, recalls that senior safety managers were deeply suspicious of Mr. Lopez. He had a prior back injury, in 2000. Worse still, he had ''jumped ship'' and been kept off work for months.

Then, in questioning Mr. Lopez, the managers discovered that he had recently bought a bass boat. They found this highly significant, Ms. Sankowsky recalls. Might he be faking injury to get his boat paid off with disability insurance? When she argued that shock was difficult to fake, Ms. Sankowsky said, the safety manager brushed her aside: ''Michelle, don't you think that you could sweat and cry a little bit if you thought you were going to get a free boat and paid vacation?''

Mr. Lopez was sent by van to the Occu-Safe clinic where, after a brief examination, he was given pain medicine and sent home, records show. The clinic doctor diagnosed a back strain and told the plant to expect Mr. Lopez back in three days. In fact, he was getting worse. He felt a creeping numbness in his legs and hands.

At Tyler Pipe, Ms. Sankowsky said, Mr. Collier and the safety managers were ''really circling their wagons around Mr. Lopez, that he's a fraud, he's a fake, and, you know, we're going to get him before he gets us.'' At a meeting on March 13, the managers approved a plan to place Mr. Lopez under surveillance, corporate records show.