Congressional Democrats for the first time named names Wednesday in their investigation of formaldehyde-contaminated travel trailers provided by FEMA to victims of Hurricanes Katrina and Rita, charging that manufacturers knew but did not disclose that the units were emitting high levels of the toxic gas that could sicken inhabitants.

At a contentious hearing before the House Oversight and Government Reform Committee, Rep. Henry Waxman of California and other Democrats grilled officials of four companies - Gulf Stream Coach Inc.; Pilgrim International Inc.; Keystone RV Inc.; and Forest River Inc. - whose trailers were found to have the highest levels of formaldehyde in testing by the federal Centers for Disease Control.

Waxman, the committee chairman, said all four companies should have known that their products contained potentially dangerous levels of formaldehyde, the airborne form of a chemical used in a wide variety of products, including composite wood and plywood panels.

But he saved his sharpest criticism for Gulf Stream, of Nappanee, Ind., which provided the Federal Emergency Management Agency with 50,000 travel trailers under two contracts worth a total of $500 million.

He said that documents reviewed by committee staff indicated the company found high levels of formaldehyde in its trailers in testing conducted in early 2006, but viewed the results as a public relations liability instead of a health hazard and failed to inform FEMA.