When I heard the recent news about the false emergency alert in Hawaii that warned a ballistic missile was incoming, my first reaction was, "That’s terrifying," followed quickly by, "What would I do if I got an alert message like that?" Perhaps you had a similar reaction. So did my colleague here at WGBH News, reporter Craig LeMoult, who was reminded of something that has long piqued his and his wife’s curiosity.

"There’s this sign on the outside of our apartment building that says 'fallout shelter.' And I’ve been wondering for the longest time, what is the deal with this sign? What does it mean, how did that get designated, and is it any safer for us?"

Of course, LeMoult's building is just one of many in our area with one of these iconic black and yellow signs. And thankfully, for him and the rest of us, there's a local citizen-historian in the area who has spent years researching and documenting the history of these signs. His own interest in them was roused some 20 years ago, as a boy.

"The middle school I attended in Boston was the William Barton Rogers Middle School [in Hyde Park] and the school had those signs on it," said Sean Colby, the citizen-historian who runs the website  Fallout Five Zero. "I started asking my parents about it, and my interest grew from there, and since then, it's been over 20 years." 

The program that led to these buildings being designated and marked as fallout shelters was launched during the Cold War. This was a time when nuclear war with Russia was a very real and rising threat; a time of duck-and-cover drills in schools and  educational films about how to build your own fallout shelter at home. 

By the early 1960s, then-President John F. Kennedy decided it was also time for a more concerted and comprehensive national safety plan. In July 1961, he gave a speech outlining a new program.

"Tomorrow I am requesting of the Congress new funds ... to identify and mark space in existing structures — public and private — that could be used as fallout shelters in case of attack," Kennedy told the nation. 

And so, the Office of Civil Defense — the precursor to FEMA — went to work.

"The Army Corps of Engineers, along with specially trained architects and engineers that were trained by them, went around the U.S. and started surveying buildings to see if they would be suitable for protection against radioactive fallout," said Colby.

Existing buildings were deemed suitable if they met three criteria: No. 1, Physical protection, which often meant they were fairly airtight, with thick concrete walls.

"They had to have a protection factor of at least 40," said Colby. "[That] meant you would receive 1/40th the radiation inside the building than you would outside, unprotected."

The second requirement was that there be space in the building at a suitable distance from likely fallout. This often meant the basements in buildings like schools, and the middle floors of taller buildings. The third criteria was sheer size.

"Room for at least 50 people with 10 square feet of space per person," said Colby.

It’s critical to understand that these buildings were designated as fallout shelters. They were only deemed protective against radioactive elements propelled into the atmosphere after a nuclear bomb strike elsewhere — like, say, New York or D.C. As for safety in the event of an actual direct strike?

"If you were in a city that received the bomb blast, you likely wouldn’t have survived," said Colby.

By the mid-1960s in Boston alone, more than 2,000 buildings in the city had been identified — and more than 1,000 of them were marked with the iconic black and yellow signs.

Phase two was to equip the spaces with minimum essentials to last two weeks, by which time the danger of any fallout was expected to have passed. This included "Civil Defense" crackers suitable to eat, water barrels that they would fill when the emergency happened, instruments to measure the radiation, sanitation kits and medical kits.

Only a portion of the designated buildings ever received equipment, and funding for the program dried up by the early 1970s. Over the years, most of the equipment has been removed. But Colby says in a few spaces — including Boston’s City Hall, which was also designated as a fallout shelter — there are still some water barrels and boxes of civil defense crackers manufactured in 1962. 

And are these more than 50-year-old crackers edible?

"Ehhh," hedged Colby. "You could probably eat them. I wouldn’t."

As for the signs, they aren’t as commonly seen as they were in the 1980s and '90s. Many have come down with buildings, or have been removed during renovations — or by vandals. But as they disappear, Colby keeps their legacy alive — with photos, maps and documents — on his website.

"It’s a really big passion for me and in my eyes, it’s a really important part of our nation’s history that sometimes gets forgotten about," he said. 

A history to be remembered and — hopefully — never relived.   

Remember, you can always let the Curiosity Desk what you have been curious about lately with a quick email to CuriosityDesk@wgbh.org.