The threat of a nuclear blast might bring back echoes of the Cold War, widely considered to have ended over 30 years ago.

But with tensions rising between Russia and NATO over Ukraine and unease between the U.S. and China over Taiwan, the prospect of nuclear war is no longer a relic of the past.

That scenario troubles Peter Kuznick, professor of history and director of the Nuclear Studies Institute at American University, who for decades has studied the effects of the nuclear bombs dropped by the U.S. on the Japanese cities of Hiroshima and Nagasaki—two devastating attacks that killed 110,000 people according to a low estimate cited by the Bulletin of the Atomic Scientists.

"Many things stand out over the years," he told Newsweek.

"The first is the devastation wreaked by these two relatively small and primitive bombs. We now estimate the Hiroshima uranium bomb to have had 16 kilotons of destructive capability and the Nagasaki bomb to be around 21 kilotons. Most modern nuclear weapons today have between 7 and 70 times that much power."

Even with those relatively small bombs, the destruction was immense. People near the center were carbonized, Kuznick said, while those who managed to survive have felt the effects their whole lives.

"They suffer from cancer and other diseases. Some have had multiple surgeries," he added. "It is often said that after a nuclear war, the survivors will envy the dead. I'm not sure that that's true, but the suffering the survivors have endured has been painful to watch."

With nuclear war in the public consciousness once again, some may be wondering how best to survive in the event of a blast.

The first damaging effects from a nuclear bomb would be an enormous fireball and a flash of heat, followed by a destructive shock wave travelling faster than the speed of sound.

How damaging this would be depends on the size of the bomb, which can vary massively, and how far a person or building is from the center of the blast. In this respect, surviving is a matter of luck.

"A 15 kiloton bomb, which is a relatively small 'tactical' bomb, would have a fireball radius of about 100 metres and cause complete destruction up to 1.6 kilometres around the epicentre," Paul Hazell, a professor of impact dynamics at the School of Engineering and Information Technology (SEIT) at the University of New South Wales, Canberra, told Newsweek.

Modern, more powerful bombs "are effectively 'city-wipers,'" Hazell said. But, there are things that will improve chances of survival in areas that would not be totally destroyed.

This includes finding a building like a concrete bunker or basement before the blast, according to Hazell. Many modern buildings have lots of glass, but this could prove dangerous.

"Buildings with glass facades would be deadly and although glass structures can withstand 'wind' loads and small blast loads to a certain extent when laminated, against a nuclear blast they would stand no chance and the resulting glass shards would be deadly—like millions of little knives being thrown faster than the speed of sound in air, which is 343 meters per second," he said.

"If you're in an apartment building, run to the fire staircase in the structural core of the building. Avoid timber, fibre cement or prefabricated structures as these probably won't survive."

According to the U.S. Centers for Disease Control and Prevention (CDC), cars will not provide good protection from radioactive material.

If caught outside, the U.S. government's Ready.gov website states people should take cover behind anything that might offer protection, lie face down and avoid touching the eyes, nose, and mouth if possible. If in a car the site advises stopping safely and ducking down within the vehicle.

After the shockwave passes, there are about 10 minutes left to find adequate shelter.

The other fatal aspect of an atomic bomb, aside from the heat and air blast, is the radiation. Again, this is something that may become less severe further away from the blast, but there's no hard rule as bombs very in size and type.

Patrick Regan is a professor of radionuclide metrology at the University of Surrey, told Newsweek that people exposed to strong enough amounts of radiation may be killed instantly—others may become sick later.

Radiation doses absorbed by a person can be measured by a unit known as a gray, with one gray being equal to an absorbed radiation dose of one joule of energy per kilogram. According to Regan, "if you fired 10 grays of radiation at [a person] over their whole body, 50 percent of them will die almost immediately, and fall over… their central nervous system gets wiped."

Even though smaller doses might not cause immediate death in those exposed, it does increase the risk of acute radiation exposure sickness and cancer in the long run.

"The way you survive is you keep the dose low," Regan said. "You can shield yourself—staying inside is good, probably. The thing about radiation fallout is it decays away relatively quickly."

The CDC advises getting inside a building as soon as possible and heading to the basement or the middle of the structure. This helps since radioactive materials settle on the outside, so staying away from walls and the roof might be a good idea.

Removing outer layers of clothing before entering will help avoid carrying radioactive materials that might have settled on the clothing into areas where people are sheltering. Once inside, washing areas of the body that were exposed to the outside will also help. Putting on clean clothing afterwards will help keep material from spreading.

The problem with sheltering is supplies, especially if caught unprepared. Foraging for them may be out of the question.

Regan used Chernobyl as an example, when "grass got contaminated, cows ate the grass, people milked the cows, and they gave the milk from the cows to babies," Regan said. "If I was advising, I'd say I wouldn't take any stuff off the ground for a bit."

"The infrastructure around you would be the most devastating thing. If you were building your own nuclear safe bunker, what do you need? You need water, tin cans, that would be good. And basically, the longer you stay in there, the better. The radioactivity drops as a function of time."

Regan said water would be another issue. According to the CDC, scientists will test drinking water supplies for radioactivity after a nuclear event, and until those results are available bottled water is the only water free of contamination. Boiling water will not help.

As such, bottled water should be kept in emergency supplies as water, juices, and other drinks in sealed containers should be safe if kept away from radiation—as will food kept in sealed containers away from radioactive sources.

The CDC also recommends wiping containers with a damp cloth or clean towel before opening them, and then putting that towel in a sealable container or plastic bag in an out-of-the-way place.

There are three main types of radiation: alpha, beta, and gamma. Gamma can go through walls but does a lot less damage because it does not interact with things much, Regan said, while an alpha particle will "kill everything in its path".

"The weird thing about that is because these alpha particles kill everything in their path they lose energy very quickly. If you put most alpha emitters on the surface of your skin, the dead layers of my skin would be enough to stop those alpha particles. What you don't want to do with that type of radioactive material is get it inside you, either by breathing it in or with food or drink. It basically gets into the blood and any cell it comes into contact with, it will kill."

The CDC also states that the walls of ones' home can block much of the harmful radiation from a nuclear event, and staying inside for at least 24 hours may provide protection while the radioactive materials weaken—though the U.S. government's advises that supplies for three or more days should be kept if possible.

These should include bottled water, packaged food, medicine, a flashlight, batteries, and a hand-crank or battery-powered radio in order to tune in to emergency broadcasts

Since radioactive particles can be carried in air, the CDC also recommends closing and locking windows and doors, going to a basement or the middle of a building, and turning off fans, air conditioners, or any other units that bring air in from outside.

This is not an exhaustive list of nuclear blast survival. More steps are outlined extensively on the CDC's website.

"The only good thing to come out of the Ukraine and Taiwan crises is that they have put the nuclear threat back in the public mind," said Kuznick.

"At least since the end of the Cold War and perhaps for a few years before that, largely because of the heroic efforts of the recently deceased Mikhail Gorbachev, most people acted as if the nuclear threat had subsided. It may have subsided, but it didn't disappear."

According to the historian, even a limited nuclear war between India and Pakistan could lead to the death of almost two billion people through famine and disease.

"Right now, Joseph Biden and Vladimir Putin have veto power over the continued existence of life on our planet," he said, "and Xi Jinping appears to be trying to join them in this lethal perversity."

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