PLYWOOD CULPRIT

Unsurprisingly, they found that processed wood products such as particleboard and plywood were the main source of formaldehyde. They did not find other chemicals at significant levels.

Formaldehyde, used to manufacture many building materials, can irritate the skin, eyes, nose and throat. High exposure levels may cause cancer.

The Department of Housing and Urban Development identified particleboard and plywood as one of the largest sources of formaldehyde emissions in 1985 and set standards for manufactured homes to limit them.

Nowak said all the relevant agencies would meet to discuss what to do.

"It has implications for FEMA as FEMA looks at emergency housing. One of the factors they need to consider is indoor air quality and the construction materials used in the ventilation systems," Nowak said.

An earlier CDC study showed average formaldehyde levels in trailers and mobile homes was about 77 parts per billion -- high enough to raise the odds of cancer and respiratory diseases.

The Manufactured Housing Institute said gypsum board was now used in 95 percent of walls and ceilings in manufactured housing.

Michael McGeehin, director of the Division of Environmental Health Hazards at CDC, said the findings only applied to trailers distributed by FEMA in the Gulf Coast Region.