Under the administration of President Kennedy, the U.S. government conducted what was known as the "National Fallout Shelter Survey." This was a campaign by the Department of Defense to identify, list and label every space in the United States that was suitable to serve as a fallout shelter.

The program had eight "protection factor" categories ranging from 1-8, with 1 providing the least protection and 8 providing the most. A PF1 shelter would provide between 20 and 39 times less radiation than an unsheltered person would receive.

A PF7 shelter would provide between 500 and 1000 times less radiation, and a PF8 shelter would provide more than 1000 times less radiation.

From the 1950s through the Cuban Missile Crisis, the federal government labeled spaces with PF4-8 protection (100 times less radiation). During the Crisis, the government decided to mark spaces with category 2-3 protection. Only spaces category 4-8 were designated to be stocked with supplies, but most of those received no supplies due to a lack of funding for the civil defense program.

If you went into a designated space today, you'd probably find a musty concrete basement. That's it. The fallout shelter designation was intended to let people know where they should go when the National Oceanic and Atmospheric Administration declared a fallout alert using the National Weather Service's network of radiation monitors. Once fallout conditions cleared (generally thought to be a period on the order of hours, rather than days), people could leave the sheltered area.

The program wasn't designed to help you survive an atomic blast right next door. It was designed to give you a space to survive the fallout from an atomic blast in the next state or city.

On Jan. 2, 1963, assistant Secretary of Defense Steuart L. Pittman sent a letter to Sen. Ernest Gruening, D-Alaska:

"Our National Fallout Shelter Survey is about 90.5 percent complete and we have just received a report of the results to date. This information is about to be released through our regional offices to the state and local Civil Defense Directors, who must have it in order to proceed with their responsibilities in connection with the National Fallout Shelter Program. However, I believe you will be interested in knowing that in the State of Alaska we have already identified 70,767 shelter spaces capable of providing from 40 to over 1000 times as much protection from nuclear fallout as would be available to an unsheltered person."

Enclosed with the letter is quite possibly the oldest computer printout I've ever seen, on two-color tri-fold paper with the punched margins and a bunch of figures identifying shelter spaces.

What's interesting if you look back at contemporary writing is how many people (particularly on the liberal side of the political spectrum) were fervently opposed to a national fallout shelter program. Sen. Gruening, who later would vote against the Tonkin Gulf Resolution, was one of these people, and he later explained that he was opposed to the program because it gave people the false belief that a nuclear war was survivable. If they believed that, he thought, the United States would be much more likely to engage in a nuclear war.

If destruction was assured, peace would be the only action left to a rational person.

So I recently did a television episode where we went into what was once a fallout shelter in a (pretty nice) Brooklyn Heights apartment building. It was just a basement at this point. Had a room that the super once lived in (which I found a little creepy, because it was a pretty OK little apartment down there, but stuffed in to the back of where the laundry room was and with almost no windows), the laundry room, and a storage space room.

So could that be a shelter? Not much of one. Maybe it would still act as a crude blast shelter — if the bomb wasn't that big, and didn't land too close, you might ride out a blast or thermal wave down there better than you might being on the surface. But maybe not — who knows how long it had been since it was last inspected for that purpose?

But it lacked the basic supplies that a working fallout shelter would have. No bottled or canned water. No food. Nothing to sleep on. No radio. The only thing it had going for it was a toilet (part of the super's apartment part) though if the plumbing stopped working that would get pretty awful pretty quick.

It is worth keeping in mind that an urban fallout shelter would ideally be a place you could live for at a minimum of several days, but ideally up to a week or so. You are waiting for the fallout particles outside to decay down to a level in which they won't harm you to evacuate through them. You don't live in fallout shelters forever (popular lore notwithstanding), and you aren't expected to survive if you happen to be unlucky enough to be in a very high pressure zone of the blast (a civilian building is not going to be able to withstand much more than 20 psi or so, and nuclear weapons can create pressures hundreds of times that depending on how they are targeted, how large they are, etc.).

I'm not sure you'd even be able to get into the shelter without someone unlocking it for you — it didn't seem like it was a publicly-accessible space. (We were let into it by the current super for the building, who stood around in the basement smoking a cigar the whole time. Seriously.)

If one were trying to take shelter from just fallout (no blast) today, those shelters would probably not be the worst places to go, but they would not be the best places to go. They would need to be carefully inspected to make sure they weren't sucking in air/dust from the outside. This report goes into depth into the kinds of structures that would be useful in the event of radioactive fallout — a modern apartment or office building is probably better than an old basement. Note that this study is specifically about low-yield, terrorist nuclear weapons, not about present-day strategic weapons, or Cold-War-era strategic weapons.

Here's a little two minute clip of the segment if you are interested. It is a little cheesy. My hair is doing some weird stuff. It was cold as hell out there the day we filmed.

This American Life just had an episode called "The Super" which referenced what had happened to the fallout shelter in one of the NYC buildings in the story. It was basically used as a storage place and was completely unusable as a fallout shelter.