This week, the federal Department of Homeland Security is testing just how many subway riders would be at risk in a nightmare scenario: terrorists releasing a deadly biological agent in the subways. NY1's Michael Herzenberg filed the following report.

It may have looked like a release of steam, but officials released particles that are meant to simulate a biological attack in the Lexington Avenue subway station at Grand Central Terminal.

It was a test to determine how a deadly biological agent like anthrax could move through the subways. The tiny particles were actually a sugary food additive.

"The sugar is approved by the FDA, so it's a non-hazardous material," said Donald Bansleben, program manager at the Department of Homeland Security.

The study of how a biological agent might spread through the system, propelled by moving trains, builds on a test three years ago of how a deadly chemical gas might spread. The new tests will include more gas sampling as well.

Some, but not all, straphangers NY1 spoke to said they appreciate the study.

"It's great to me," said one straphanger.

"Be prepared," said another. "I don't know if it's going to do any good, but why not take a chance and see what happens?"

"It's just a waste of taxpayers' money," said a third.

Officials say 200 devices will monitor the air at 60 subway stations, most in Manhattan, and at one PATH station in New Jersey. More data will be collected through cloth squares and filters worn by contractors.

"It is for collecting particles on the cloth, and we're also going to collect dosage measurements on us with little filters, and we do comparisons of that to see what lands on people," said David Brown of Argonne National Laboratories.

During the week, the particles and gas will be released throughout the day at subway stations beneath Times Square and Penn Station, in addition to Grand Central. First responders anxiously await the results.

"It will help us better understand where to shelter in place, where to evacuate from, how far and if personal protective equipment is necessary for our responders," said Batallion Chief Bob Ingram of the FDNY.

The testing concludes Friday. The feds say the results will take at least six months to process and publish for the MTA and other agencies.