Data from the World Trade Center Health Registry show that 3.6 percent of the 25,000 rescue and recovery workers enrolled reported developing asthma after working at the disaster site, the New York City Health Department said Monday.

That figure is 12 times higher than would normally be expected for the adult population during such a time period.

Workers who arrived on September 11, 2001, and worked more than 90 days reported the highest rate of new asthma. Respirator use increased as the clean-up progressed, reducing the risk to later workers, the report said.

"The dust from the World Trade Center collapse appears to have had significant respiratory health effects at least for people who worked at the site,” Dr. Thomas R. Frieden, New York City health commissioner, said in a statement. "These findings reflect the critical importance of getting appropriate respiratory protection to all workers as quickly as possible during a disaster, and making every effort to make sure workers wear them at all times."