There are so many ways to be brave in this world. Sometimes it is nothing more than gritting your teeth through the pain, and the work of every day, the slow walk toward a better life. Sometimes bravery involves laying down your life for something bigger than yourself, or for someone else. Sometimes it involves giving up everything you have ever known, or everyone you have ever loved, for the sake of something greater.

You probably don’t know their names, but 30 years ago, three unsung heroes saved Europe. On April 26, 1986, the world experienced the worst ever nuclear disaster. It occurred at the Chernobyl Nuclear Power Plant in Ukraine.

The Chernobyl Disaster was the worst nuclear accident of the 20th century and is definitely one of the most devastating tragedies that happened during that era. The disaster claimed at least 985,000 lives during and after the accident, most due to exposure to the harmful radiation. The first responders to the disaster are remembered today through a database called the Remembrance Book and a monument in the city of Chernobyl, with a plaque that says “To those who saved the world”.

However, there are three names that are often forgotten when people talk about the first responders who helped clean up after the disaster. These three men didn’t just help in the cleanup efforts, they managed to prevent a large-scale disaster that might have affected Europe, Asia, and Africa.

The Chernobyl Nuclear power plant’s water-cooling system had failed, and a pool had formed directly under the highly radioactive reactor. With no cooling, it was just going to be a matter of time before a lava-like substance melted through the remaining barriers, dropping the reactor’s core into the pool. If this would have happened, it might have set off steam explosions, firing radiation high and wide into the sky, spreading across parts of Europe, Asia, and Africa.

Plant engineers Alexei Ananenko and Valeri Bezpalov, and shift supervisor Boris Baranov were given an important mission after the disaster: to dive into radioactive waters and release the critical pressure valve. They were chosen specifically because Ananenko was the only one who knew where the valve was located.

The three men were told of the health risks should they choose to take up the mission, they were also given the choice to refuse. Ananenko replied, “How could I do that when I was the only person on the shift who knew where the valves were located?”

With that, Ananenko, Bezpalov, and Baranov dived into more than 5 million gallons of contaminated water. They managed to release the valves in time and saved the world from experiencing another nuclear explosion. By the time the men surfaced from under the reactor, all three were showing signs of severe radiation poisoning.

Ananenko, Bezpalov, and Baranov passed away after two weeks.

Here is to those brave souls that risked their lives to save half of humanity.