With President Donald Trump discussing nuclear war with North Korea as a possibility, the thought of surviving a nuclear attack is a thought crossing people’s minds more and more. Weapons of mass destruction exist, but contrary to popular belief, survival is possible. Learn how to survive a nuclear war, ahead.

About nuclear war specialist Cresson Kearny

The author of the best-selling survival manual, Nuclear War Survival Skills, Cresson Kearny, was not only an author but an inventor and expert on jungle warfare, according to The New York Times. ”Throughout his life he believed in being prepared for trouble,” Kearny’s daughter, Stephanie, told The New York Times. Learn Kearny’s tips for surviving a nuclear attack, below.

Hint: There’s a chance you can survive a nuclear attack.

Survival is possible

A nuclear war “would be far from the end of human life on earth,” according to Kearny. “The dangers from nuclear weapons have been distorted and exaggerated, for varied reasons.” Don’t think a nuclear attack means imminent death. “These exaggerations have become demoralizing myths,” Kearny said.

Hint: Use concrete or brick to build a shelter.

Shelters require lots of material

“The denser a substance, the better it serves for shielding material,” according to Kearny. Concrete or brick would be ideal materials for a shelter. However, a shelter made with dense materials close to the ground zero will not perform as well as a shelter of lesser quality further away from the blast. Learn why, next.

Hint: People can survive in shelters without doors.

Don’t discount air raid tunnels

In the Japanese city of Nagasaki, some people survived the atomic bomb. “Some people survived uninjured who were far inside tunnel shelters built for conventional air raids and located as close as one-third mile from ground zero,” Kearny said. “This was true even though these long, large shelters lacked blast doors and were deep inside the zone within which all buildings were destroyed.”

Hint: The atomic bomb dropped on Nagasaki taught us valuable survival information.

What Nagasaki taught us

The takeaway from the survivors of Nagasaki is this: “People far inside long, large, open shelters are better protected than are those inside small, open shelters,” according to Kearny. Build a fallout shelter accordingly. History shows us that people survived a nuclear bomb with the proper shelter.

Hint: Fallout shelters and do without this one thing.

The air in fallout shelters is safe

“The air in properly designed fallout shelters, even those without air filters, is free of radioactive particles and safe to breathe except in a few rare environments,” Kearny said. Don’t think because your shelter doesn’t have an air filter, you’ll die. The rare environments mentioned by Kearny include “areas of extremely heavy fallout,” such as areas downwind from the blast.

Hint: Don’t expect to live in a fallout shelter for the rest of your life.

You won’t have to stay in a shelter forever

“Fortunately for all living things, the danger from fallout radiation lessens with time,” Kearny said. “The radioactive decay, as this lessening is called, is rapid at first, then gets slower and slower.” People can stop using most shelters within two weeks of a nuclear attack or could work outside for hours at a time. Know when it’s safe by using a fallout meter to measure radiation.

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Read more: What the Aftermath of a Nuclear War With North Korea Would Actually Look Like