"There is no safe level (of exposure) to prevent chronic beryllium disease," a wasting lung ailment, said David Egilman, a professor at Brown University and director of a medical clinic.

Egilman testified on behalf of four Rocky Flats workers and their wives who are suing Brush Wellman, an Ohio-based company that supplied beryllium to the former nuclear weapons plant.

The lawsuit alleges that the company covered up what it knew about the toxicity of the metal and conspired with the federal government to accomplish that.

In articles and books stretching from the 1960s to the 1990s, company officials said that no workers became ill from exposures to 2 micrograms or less of dust or fumes from the metal, which is the federal safety standard.

But the company founder and president wrote in his private diary in 1951 that Brush employees were getting the disease when exposed to dust or fumes below the safety standard. That diary and other company documents were introduced earlier in the case.

Two of the workers also testified Thursday that the conditions in their work area at Rocky Flats were clean.

"They were very clean, I thought," said Salvador Valencia, a 53-year-old who machined the metal at the plant for about eight months in the 1970s.

Brush has tried to show government contractors operated the plant under unsafe conditions because workers didn't have proper ventilation and were allowed to eat around the metal's dust.

Valencia said that he was never told to wear a respirator when he machined beryllium, and there was no special ventilation.

James Tooley, another worker in the lawsuit, testified he was exposed to fumes during an accident while he was distilling dissolved beryllium metal as a lab worker.