(CNN) -- Rep. Nick Lampson, D-Texas, said Tuesday that Federal Emergency Management Agency tried to control the outcome of a scientific study on formaldehyde in trailers used to house victims of Hurricane Katrina.
FEMA trailers are shipped to the Gulf Coast by train in March 2006.
"Someone from one of the agencies, the CDC, came to our committee and reported that he had information that indicated that good science wasn't followed when a decision was made to allow people to live in basically travel trailers that were not designed to be lived in," said Lampson, chairman of the Energy and Environment Subcommittee of the House Committee on Science and Technology.
In addition, the chairman of the House Homeland Security Committee -- Rep. Bennie G. Thompson, D-Mississippi -- cited medical experts who said prolonged exposure to high levels of formaldehyde can cause ailments ranging from respiratory irritation to cancer.
The committee recently obtained internal CDC e-mail which showed that "despite the efforts of CDC professionals to bring these health risks to the public's attention, those concerns were thwarted by CDC leadership for roughly eight months," Thompson said.
FEMA denies that it has suppressed any report, including one about formaldehyde prepared by a branch of the Centers for Disease Control.
"The health and safety of residents has been and continues to be our primary concern," FEMA said in a statement issued Monday. Watch why the trailers are such a big concern »
"Any and all allegations that FEMA ignored or manipulated formaldehyde-related research are unfounded and false. Such activities are completely contrary to our mission and our commitment to the victims of disaster," said Carlos Castillo, FEMA's assistant administrator for disaster assistance during the House Homeland Security Committee hearing Tuesday afternoon.
Almost 150,000 households have lived in FEMA trailers at some point since Hurricanes Katrina and Rita devastated the Gulf Coast in 2005. FEMA says about 40,000 families are still living in the travel trailers.
Formaldehyde is a preservative used in construction materials like plywood. The Environmental Protection Agency classifies it as a probable human carcinogen, according to the EPA Web site.
The site says the chemical can also be an irritant to the respiratory tract and the eyes. FEMA and the CDC say the Agency for Toxic Substances and Disease Registry, an arm of the CDC, did an initial assessment for FEMA that wasn't intended to address the long-term effects of extended exposure to formaldehyde.
"ATSDR's original response focused on the acute health effects of formaldehyde exposure -- to meet the urgent needs expressed by FEMA in its original request," said a CDC statement.
"The initial consultation with ATSDR was intended to determine effective mitigation measures, and did not discuss long-term health impacts," a FEMA statement agreed.
"FEMA wanted to be able to put people into these trailers for long periods of time," Lampson said. "They gave a report that apparently said that it was safe to go in for a couple of weeks and allowed people to go in. Well, it's been way past a couple of weeks and now people have been in them a year or 18 months."
"One person [from the CDC] who came to us told us they wouldn't write the report," he said. "That person was circumvented and another person at the agency agreed to write a report to say that levels of formaldehyde were safe for a couple of weeks."
FEMA received that initial report in February 2007. "That study showed that ventilating the units is effective in reducing levels of formaldehyde," according to a FEMA fact sheet.
FEMA and the CDC said it became apparent that more study was needed, so ATSDR went back to work and issued a new report in October.
"This revised report supports the initial report in that ventilation of travel trailers was effective in lowering formaldehyde levels," according to the FEMA statement issued Monday. "It was revised to include a number of caveats relating to potential health impacts of long term exposure."
FEMA says it has offered everyone living in a travel trailer the option of moving to a hotel until alternative housing can be found. Meanwhile, the CDC has been doing a separate study of formaldehyde in the trailers.
The results of that research are expected next month. FEMA pointed to that more comprehensive study in its statement issued Monday about the controversy, and added, "In addition, FEMA already had begun an aggressive outreach campaign to occupants advising them of potential exposure to formaldehyde and offered those residents an option for immediate relocation to alternative housing," the FEMA statement said.
Lampson said his subcommittee has requested copies of communications between FEMA and the CDC on the subject.
"Not following good science in advising people to do things as they try to recover from one tragedy is indeed a much greater tragedy this is compounding," he said. "This appears perhaps to be the tip of an iceberg." E-mail to a friend
CNN's Sean Callebs and Eric Marrapodi contributed to this report.