The high levels of formaldehyde found in the indoor air of trailers used for Hurricane Katrina evacuees came primarily from processed wood products such as particleboard and plywood, federal scientists say. Researchers at Lawrence Berkeley National Laboratory examined four trailers and detected formaldehyde at levels four to 11 times higher than those typically found in U.S. homes. They also found elevated levels of two other volatile organic compounds, phenol and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, but not at concentrations high enough to pose health hazards. "Even with a limited sample of trailers, this study affirms what would be expected: that construction materials that emit high concentrations of formaldehyde, when part of a relatively small structure that has poor ventilation, have the potential to produce elevated levels of formaldehyde in the indoor air," says Michael A. McGeehin, director of the Division of Environmental Hazards & Health Effects at the U.S. Centers for Disease Control & Prevention. "This suggests that efforts to design and build emergency housing units may be able to greatly improve indoor air quality by using different construction materials and ensuring that ventilation systems let in fresh air."