While the Federal Emergency Management Agency rushes to move thousands of Gulf Coast storm victims out of government-issued trailers, scientists are tearing the units apart to learn why many have exposed occupants to dangerous levels of formaldehyde fumes.

The U.S. Centers for Disease Control and Prevention is studying materials used by several companies that provided FEMA with tens of thousands of travel trailers after hurricanes Katrina and Rita in 2005.

Test results reported Thursday by the CDC showed formaldehyde levels in hundreds of FEMA trailers and mobile homes were, on average, about five times higher than what people are exposed to in most modern homes. Formaldehyde, a preservative commonly used in construction materials, can cause breathing problems and also is believed to cause cancer.

CDC director Dr. Julie Gerberding said scientists need time to determine how and why formaldehyde levels varied among different models of FEMA trailers. Scientists from the CDC and the University of California's Lawrence Berkeley National Laboratory also are looking at ways to reduce formaldehyde emissions in the trailers.

The study was limited to materials in unoccupied government trailers. Gerberding said other studies indicate formaldehyde levels in manufactured homes are steadily decreasing "in a fairly significant manner."

"Mainly because the manufacturers don't want this problem," she said Thursday, "so they're learning how to use new materials and changing their processing."

Kevin Broom, spokesman for the Recreation Vehicle Industry Association, said Friday that the industry will adjust its manufacturing techniques if the government adopts stricter formaldehyde standards than those already set by the U.S. Department of Housing and Urban Development.

"We in the RV industry are committed to following the science and making sure our products are safe," Broom said in a prepared statement.

FEMA, which hopes to move roughly 35,000 trailer occupants into apartments, hotels and other housing by summer, says its New Orleans office fielded nearly 70 phone calls from concerned residents after Thursday's announcement.

Sherry Gremillion, 45, a waitress still living in a St. Bernard Parish trailer park, said she can't afford an apartment large enough to accommodate her family or close enough to her job. FEMA expects to close the trailer park by March 15 and is trying to help find her a new place to live.

"I fell asleep crying last night," she said Friday. "I don't think I'm going to make it."

Hundreds of Gulf Coast trailer dwellers are suing manufacturers in federal court, accusing the companies of furnishing FEMA with shoddily constructed units that jeopardized their health. By law, FEMA can't be named as a defendant in the consolidated litigation until next month, at the earliest, according to plaintiffs lawyers.

Critics claim FEMA should have reacted sooner to concerns that formaldehyde is to blame for a host of ailments reported by trailer occupants.

"They knew full well something was wrong. They were just hoping nothing would happen," said attorney Daniel Becnel Jr., who says he represents about 5,000 trailer occupants.

Another plaintiffs lawyer said trailer makers are the "real culprits."

"Obviously FEMA made lots of mistakes, but FEMA didn't manufacture these trailers," said Tony Buzbee, a Galveston, Texas-based lawyer for hundreds of current and former trailer occupants.

A lawyer for the companies sued in U.S. District Court in New Orleans didn't immediately return a telephone call for comment Friday.

During Thursday's press conference, FEMA administrator R. David Paulison said the agency hopes to move all of the roughly 35,000 families out of trailers by summer, when hot weather increases formaldehyde emissions.

"It's easier (in Louisiana) than it is in Mississippi," Paulison said. "More housing is coming on every day in Louisiana. Not so much in Mississippi."

Louisiana currently has 25,162 occupied FEMA trailers and mobile homes, while Mississippi has 10,362, according to FEMA. The number of occupied FEMA trailers and mobile homes peaked at 144,000 following the 2005 hurricanes.

Paulison said the relocations are a "stopgap measure."

"We're not booting people out. What we're doing to putting them into hotels and motels until we can find an apartment for them," he said. "It's just transition, to get them out of the travel trailer and into someplace where it's safer."

Most of the residents left in FEMA trailer parks are the elderly and those with disabilities, people on fixed incomes who often can't easily find affordable housing, said Tracie Washington, president of the Louisiana Justice Institute, a nonprofit advocacy group for the poor.

"These are people that rented $200, $300 apartments before Hurricane Katrina, and those aren't available anymore," Washington said. "They're afraid that if they're moved into hotels they'll wind up homeless in a few months."

An estimated 1,550 residents of Jefferson Parish, in suburban New Orleans, are still living in trailers. Parish officials want them all out of trailers by March 1, but that push isn't linked to FEMA's announcement Thursday, said Louis Savoye, the parish's director of inspection and code enforcement.

"We feel the vast majority of citizens have recovered," he said.

Associated Press writers John Moreno Gonzales, Mary Foster and Becky Bohrer in New Orleans contributed to this story.