"We haven't yet received the avalanche of claims that might have been expected," she said, adding that only about 300 people had filed so far. She predicted thousands would file.
Nearly two years after President Obama signed the James Zadroga 9/11 Health and Compensation Act into law, about 40,000 responders and survivors receive monitoring and 20,000 get treatment for illnesses as part of the World Trade Center Health Program, one of the law's two components. But the other, Birnbaum's fund to compensate the same categories of people for economic losses, has been slower to get off the ground.
It's not a matter of bureaucratic foot-dragging, but an illustration of the complexities of key legislation born of the attacks that took place 11 years ago next week.
"This is a lot more complicated than meets the eye," said Birnbaum.
With time still left to submit claims, some people are holding out in the event that they become sick. Others are waiting until the National Institute for Occupational Safety and Health officially adds to its list 14 broad categories of cancer.
The national institute's director, John Howard, said in June that it planned to expand coverage to include scores of cancer types.
Recently found to have leukemia and lymphoma, 55-year-old Brian Casse hopes he can secure money from the fund to support his wife and children in case he takes a turn for the worse. Casse, a retired firefighter who helped clear away the mountain of rubble at ground zero, says he believes there is little doubt his work at the site is responsible for his illness.
"You've got people in this city who went down there and did what we had to do. And a lot of us got sick because of it," Casse said. "To make us now fight for this money, it's not right. In the grand scheme of things, this money's a drop in the bucket."
Initially, the Zadroga Act - named for police Detective James Zadroga, who died at 34 after working at ground zero - included only a short list of illnesses that qualified for compensation. Cancer was excluded because of a lack of scientific evidence linking any form of the disease to conditions in the debris pile.
"To me, it's common sense. If you breathe in toxic fumes, you're going to get cancer," said U.S. Rep. Carolyn Maloney, a Manhattan Democrat who coauthored the bill.
But even Maloney conceded that it is difficult to find hard data proving the connection between cancer and the dust at ground zero. That's why in crafting the Zadroga Act, lawmakers were careful to include mechanisms that would allow for illnesses to be added based on new scientific research.
An inclusion of cancer on the list will likely encourage more people to file claims. Applicants will have to provide evidence of diagnosis and time spent at ground zero, though they do not need to enroll in the health program.
The fund has $875 million to distribute in its first five years. The rest of the money will become available in its sixth year, so recipients will get their awards in two payments.
"If people's expectations were that they were going to get a whole bunch of money immediately, that's not the way the fund was set up," she said. "We're going to do this in a fair and transparent way."
It's a tricky job, especially considering that Birnbaum assumed her role with no structure in place. In just a few months, her team of 50 had to write up legal documents, set up computer programs to analyze claims, and launch an operation that would distribute the funds equitably.
"Everything had to be created from scratch," said Birnbaum. She is not paid for her work on the fund.
Birnbaum acknowledges she can afford no mistakes. If Congress isn't happy with how she handles the distribution, the fund risks losing political support when advocates push for reauthorization after 2016.
The fund, which Congress originally established in 2001 to prevent potentially devastating class-action lawsuits against the airlines whose planes were hijacked and used in the 9/11 attacks, gave $6 billion to the families of victims and $1 billion to the injured.
When it closed in 2003, however, those whose injuries materialized years later were left unable to benefit. That group included workers and volunteers, many suffering from chronic respiratory problems after being exposed to clouds of pulverized building materials at the site.
On Dec. 22, 2010, in a last-minute compromise during the final hours of its legislative session, Congress reopened the fund when it passed the $4.2 billion Zadroga Act.
In the run-up to the Zadroga Act's passage, some fiscally conservative Republican lawmakers were reluctant to support the bill, citing concerns over the cost of a multibillion-dollar entitlement program.
Sen. Tom Coburn (R., Okla.) led the charge on a Republican filibuster before striking a deal with Democrats to reduce the package by $2 billion. It won unanimous consent in the Senate, and the House approved it hours later.
Advocates say they are mindful of how difficult the process was in 2010 when looking ahead to possible reauthorization.