Explainer: Perfluorocarbons, the Gas Released In NYC's Subway Airflow Test

When researchers released a tracer gas containing a chemical called perfluorocarbon into New York's subway on Tuesday, it didn't take long for people to wonder if that so-called nontoxic gas might not be all that harmless. Short answer: it's safe. Long answer: the chemical was developed for use in the Manhattan Project.

But back to Tuesday. When word of the experiment hit the public consciousness, there were a number of reactions, many in the 'WTF' department. Faux NYPD pamphlets were circulated, linking perfluorocarbons (PFCs) to early menopause and cancer. The pamphlets were taken at face value by at least one website, causing Twitter users to erupt with comparisons to chemical warfare and poison.

Not helping PFC's public image is the very real fact that it's listed by the EPA as a greenhouse gas.

The lead researcher in charge of the subway airflow study says the PFCs released Tuesday will have no measurable impact on either the environment or people's health.

"There are toxicology studies that show the material is nontoxic to levels of hundreds of thousands of times higher than the concentration we’re dealing with," said Brookhaven engineer Paul Kalb. "We’ve been working with that material for 40 years, in many many types of scientific studies, with absolutely no health impacts recorded or measured, at all."

He reiterated that the amount of PFCs released in NYC on Tuesday was tiny -- "roughly gram quantities," he said, although he wouldn't be pinned down to the exact amount.

So why use it at all?

According to Kalb, it's one of the few materials that can be used as a tracer gas -- meaning it's unique, and can be measured down to minute quantities to see where it flows. Alternative tracer options have drawbacks. 

"The only other thing you can use is a radioactive material," said Kalb, "and certainly you don’t want to do that."

PFCs aren't naturally occurring but are manufactured for healthcare: they are used in medical imaging, to treat lung injuries, and in eye surgery.

Besides, Kalb said, PFCs are already in the atmosphere, so Tuesday's test won't mean more than a drop in the ocean of PFC to inhale on NYC streets.

In fact, one of Brookhaven's tasks will be to distinguish between the 'background' PFC level and the tracer PFCs used for the S-SAFE study.

Which raises the question: if PFCs aren't naturally occurring, why are they in the atmosphere at all?

This was the moment when Kalb revealed the nuclear connection: PFCs were originally developed for use during the Manhattan Project.

"And [the PFCs] don't get destroyed," he said. "So they're in the atmosphere and they stay in the atmosphere... it essentially does not degrade and it's pretty permanent, just like other greenhouse gases, and that's the problem with greenhouse gases, once they're out there they're there for a long time."

So the current global PFC background level is a byproduct of the Manhattan project. Mull that over for a moment.

Kalb said Tuesday's PFC release was so small, it won't affect the PFC background level. "Because the amount of materials we're putting out gets diluted in the atmosphere, it's not measurable...we can’t go out enough decimal points to compute the amount that we've added to the atmosphere."

"In terms of relative risk," he added, "what makes me scratch my head is people are exposed to real things: people walk down the streets of Manhattan and they stand next to a diesel truck and don't think twice about it."