When a massive gas line explosion leveled two buildings in Harlem a few months ago, first responders found a scene of chaos. Amongst the rubble, at least a few people had already been killed. Others still were in the process of dying, and need immediate medical attention, but how to quickly identify them amongst the bedlam of 70 other victims, all scared, shell-shocked and screaming?

The same problem unfolds in most mass casualty scenarios, whether a natural disaster or a terrorist attack. And if you look closely at the aftermath photos of these gruesome scenes, you will usually see a lanyard hanging around the necks of the wounded, with a color-coded strip of paper at the end. This simple invention is the Medical Emergency Triage Tag, or METTAG, and it's saved countless lives.

From the French verb trier, meaning to sift, the triage tag allows first responders to quickly categorize patients, directing medical attention to those most in need while channeling it away from the superficially wounded or already dead. It's essentially medical rationing, in scenarios of chaos and limited medical resources.

A "victim" is attended to at a triage center onshore during a mock rescue drill simulating a boating accident in waters off the coast of San Diego, California March 5, 2014. Lifeguards, police, fire and Coast Guard personnel joined together to assess their ability to respond and learn from the training exercise.Photo by Mike Blake, Reuters

The roots of triage extend as far back as the battlefield amputations of the Napoleonic Wars, but the simple, graphic design of the triage tag itself is a legacy of the Cuban Missile Crisis. It's the invention of an unheralded civil defense director from Jacksonville, Florida who believed that nukes would be dropping on us at any second now. And While the War On Terror has inspired many redesigns, the triage tag has largely remains unchanged since the early 1960s.

As we enter the era of wearable health trackers that beam our biometrics into the cloud, it seems almost quaint that over the last 50 years the triage tag has largely resisted technological upgrades. But the METTAG is a lesson to anyone who develops human devices: the most timeless designs are often the simplest ones. And in the case of triage tags, that simplicity saves lives.

On October 14, 1962, an American U-2 Aircraft scanning Cuba brought back reconnaissance photographs providing clear evidence that the Soviet Union had set-up medium and intermediate range nuclear missiles just 90 miles off the coast of Florida. For the first time, it seemed possible–even probable–that the atomic monster America had itself created just twenty years earlier could find its way home. As children huddled under under their school desks during drills, and air raid sirens blared across remote American towns, people scrambled to make sense of a new world in which even the most idyllic city square was just a launch code away from becoming a battlefield.

One of the implied ground zeroes of a nuclear strike was Florida. And that's where a Civil Defense Director named Robert F. Blodgett came up with the idea for the Medical Emergency Triage Tag, or METTAG. The simple, two-sided laminated card is hung around the neck of an injured person as a way to communicate to first-responders the severity of their need. It's designed to be usable in any language, without localization, featuring symbols representing concepts such as blood pressure, time, sex, date of birth, address, pulse and so on.

As an active member of The American Civil Defense Association (TACDA), an organization founded to promote emergency and disaster preparedness, Blodgett was the kind of guy who went around to local schools and taught students to duck-and-cover during the height of Cold War paranoia. Blodgett printed the tags himself and distributed them to local civil defense organizations throughout the 1960's.

In 1975, he gave the design to TACDA, which started selling bundles of METTAGs nation-wide in the pages of The Journal Of Civil Defense, a magazine dedicated to raising awareness about civil preparedness for both natural and manmade disasters

"People were setting up bomb shelters, and everyone was worried about civil defense, about what we would do if the Russians did attack," according to Janice Tyliczka, who worked for TACDA as Staff Coordinator throughout the 1970's. "They sold like hotcakes." In the heyday of the METTAG, TACDA might sell upwards of 100,000 tags every year to agencies around the world. METTAG sales alone kept TACDA afloat for many years.