Newsday

The survey's results, released Monday, also indicate that respirators helped reduce the risk of developing asthma.

The study sheds new light on the health effects of exposure to dust and debris among workers who responded to the World Trade Center attacks on Sept. 11, 2001, health officials said.

The data, drawn from the World Trade Center Health Registry, show that 3.6 percent of the 25,000 rescue and recovery workers enrolled in the registry reported developing asthma after working at the site.

That rate is 12 times what would be normally expected for the adult population during such a time period, the health officials said.

The paper was published online Monday in the journal Environmental Health Perspectives.

The survey, conducted in 2003 and 2004, found that arriving soon after the buildings collapsed or working on the Ground Zero pile over a long period increased workers' risk of developing asthma.

Workers who arrived at the site on 9/11 and worked more than 90 days reported the highest rate of new asthma, 7 percent.

Though respirator use increased as the cleanup progressed, many workers did not wear respiratory protection at first.

Workers who wore respirators on Sept. 11 and 12, 2001, reported newly diagnosed asthma at lower rates -- 4.0 percent and 2.9 percent, respectively -- than those who did not -- 6.3 percent and 4.5 percent, respectively.

The longer the period of not wearing masks or respirators, the greater the risk, the survey found.

"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 Frieden, 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," Frieden said.