New York ? James Zadroga spent 16 hours a day toiling in the World Trade Center ruins for a month, breathing in debris-choked air. Timothy Keller said he coughed up bits of gravel from his lungs after Sept. 11, 2001. Felix Hernandez spent days at the site helping to search for victims.

All three men died in the past seven months of what their families and colleagues say were persistent respiratory illnesses directly caused by their work at ground zero.

While thousands of people who either worked at or lived near the site have reported ailments such as “trade center cough” since the terrorist attacks, some say that only now are the consequences of working at the site becoming heartbreakingly clear.

“I’m very fearful,” said Donald Faeth, an emergency medical technician and officer in a union with two of the ground zero workers who died last year. “I think that there are several people who died that day and didn’t realize that they died that day.”

Some officials say it is too early to draw that conclusion. Doctors running different health screening programs say it will take decades to get a clear picture of the long-term health effects of working at ground zero.

The city Department of Health and Mental Hygiene, which is tracking the health of 71,000 people exposed to 9-11 dust and debris, said last week that it is too soon to say whether any deaths or illnesses among its enrolled members are linked to trade center exposure.

David Worby, an attorney representing more than 5,000 plaintiffs suing those who supervised the cleanup over their illnesses, said 21 of his clients have died of 9-11-related diseases since mid-2004.

“This is just the tip of the iceberg,” Worby said.