CAMARILLO, Calif. — If North Korea fires nuclear missiles at Los Angeles, Dr. Robert Levin might seek protection from fallout by wedging himself into the crawl space under his Ojai home.

If the Ventura County public health officer were at the Oxnard office decorated with a photo of him administering a flu shot, he would rush to a hallway in the center of the two-story building and wait.

"Get inside. Stay inside. Stay tuned," Levin said, explaining the importance of the phrase that is his mantra. "It would save hundreds of thousands of lives. Locate yourself as far away from the roof and the walls as possible."

Four years ago, Levin guided the public health department in a nuclear readiness campaign described by preparedness experts as the first of its kind since the Cold War.

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Before that, he led efforts to compile an equally rare 243-page nuclear response plan for Ventura County that dives into strategies ranging from the 2 million people who might flee north from Los Angeles to the trenches that could be used for temporary storage of corpses.

Back then, in town halls and newspaper interviews, Levin carefully explained there is no known or immediate threat of a nuclear explosion. On Tuesday, the public health officer pointed at the exchange of threats of destruction between President Trump and North Korea's Kim Jong-un as proof of the need for readiness.

"It gives us a teachable moment," said Levin, who spoke about preparedness at a January conference near the nation's capital.

If a nuclear bomb the size of those used on Nagasaki and Hiroshima were aimed at Southern California, it might be targeted at the densest population pocket — Los Angeles, Levin said. Nearly all of the people living within nine blocks of the explosion would likely die in the blast.

If the bomb were bigger, as is likely in a North Korea scenario, more would die.

In Ventura County, people might have a narrow window of time, maybe 10 minutes, to find a building for shelter before the risk of fallout became deadly. They should retreat into the nearest biggest building and stay there, Levin said.

They should fight the urge to retrieve their children from school, knowing the kids are likely safer there. They should resist the temptation to drive as far away as possible in an almost certainly failed attempt to outrun the fallout.

Basements are best but are nearly non-existent in Ventura County, as they are in other parts of the U.S. Instead, people should go to the center of a building as far from outdoors as possible.

And they should stay there, Levin said.

Radiation levels would likely decrease every seven hours all the way to 10% of the previous level, Levin said. If a bomb the size of the Nagasaki and Hiroshima weapons were used, people might be able to leave shelters in two to four days.

But they shouldn't leave the shelter until government officials say it's safe. They should keep up with disaster news through TVs, cellphones and battery- or crank-powered radios.

The county response plan offers exhausting detail. Wash hair with shampoo only because conditioner may cause radiation to bind into hair. People should bring pets to a shelter and should dust or wash them free of any radioactive particles while wearing a face mask.

Work on the plan started more than a decade ago but Levin's interest dates further back. He started thinking of nuclear preparedness after the terrorist attacks of Sept. 11, 2001, pushed by the promises made by Osama bin Laden to destroy and disrupt American life.

"To me with all the tools that a terrorist has, nothing does that more efficiently than an improvised nuclear device," he said.

The unprecedented education campaign included town hall meetings, curriculum plans for teachers and pocket-sized guides. There was a website that remains operational. A series of slickly produced videos showed people reacting to mushroom clouds. In one, a survivor breaks into song.

"You don't need to be scared. You don't need to be loud," he sings. "Because you can survive even a mushroom cloud."

Robert Jervis is a cynic. The international affairs professor and security expert from Columbia University said it's unlikely North Korea has the capability to wage a nuclear attack on the United States. That belief makes him scoff at the county's preparedness efforts.

"There are some things that may be so unlikely that I wouldn't put a whole helluva lot of effort to prepare for," he said.

Others cite North Korea as one more reason to be ready.

"I think we're all paying attention to the media," said Ventura County Superintendent of Schools Stan Mantooth, citing reports on the White House's interaction with Kim and others. And if someday there is an attack, the county's office of education would have a plan.

"We all would immediately go into lockdown mode and try to condense the school and staff into as central a place as possible," Mantooth said.

Levin challenged the premise that if there were an attack, preparedness wouldn't matter because everyone would be dead.

"The original death toll comes from the blast itself, the explosion, but after that the deaths are associated with fallout," he said. "And we could take a great percentage of those out of the question if people would just 'get inside, stay inside and stay tuned.'"

He wants the saying to become a catchphrase so ingrained it becomes an instinct, like "stop, drop and roll." He acknowledged the goal is far from reach.

"If you queried 1,000 people in Ventura County, 20 or 30 would know," he said, rejecting the notion that talk of mushroom clouds and fallout creates panic.

"All people want is to know what to do to protect themselves and their loved ones," he said.

Besides, he said, fear already exists because of promises that the U.S. will, if provoked, destroy North Korea, bringing counterpledges that the latter country's missiles will ultimately reach America.

Levin called it saber-rattling. He also noted it hasn't made him afraid yet.

"I'm foolish enough to believe no one would be foolish enough to do it," he said.

For more information, check out the federal government's nuclear explosion preparation and survival tips here.

In case of a nuclear blast

• Listen for official information and follow the instructions provided by emergency response personnel.

• If an attack warning is issued, take cover as quickly as you can, below ground if possible, and stay there until instructed to do otherwise.

• Find the nearest building, preferably built of brick or concrete, and go inside to avoid any radioactive material outside.

• If better shelter, such as a multi-story building or basement can be reached within a few minutes, go there immediately.

• Go as far below ground as possible or in the center of a tall building.

• During the time with the highest radiation levels it is safest to stay inside, sheltered away from the radioactive material outside.

• Radiation levels are extremely dangerous after a nuclear detonation but the levels reduce rapidly.

• Expect to stay inside for at least 24 hours unless told otherwise by authorities.

• When evacuating is in your best interest, you will be instructed to do so. All available methods of communication will be used to provide news and/or instructions.

If you are caught outside and unable to get inside immediately:

• Do not look at the flash or fireball — it can blind you.

• Take cover behind anything that might offer protection.

• Lie flat on the ground and cover your head. If the explosion is some distance away, it could take 30 seconds or more for the blast wave to hit.

• Take shelter as soon as you can, even if you are many miles from ground zero where the attack occurred — radioactive fallout can be carried by the winds for hundreds of miles.

• If you were outside during or after the blast, get clean as soon as possible, to remove radioactive material that may have settled on your body.

• Remove your clothing to keep radioactive material from spreading. Removing the outer layer of clothing can remove up to 90% of radioactive material.

• If practical, place your contaminated clothing in a plastic bag and seal or tie the bag. Place the bag as far away as possible from humans and animals so that the radiation it gives off does not affect others.

• When possible, take a shower with lots of soap and water to help remove radioactive contamination. Do not scrub or scratch the skin.

• Wash your hair with shampoo or soap and water. Do not use conditioner in your hair because it will bind radioactive material to your hair, keeping it from rinsing out easily.

• Gently blow your nose and wipe your eyelids and eyelashes with a clean wet cloth. Gently wipe your ears.

• If you cannot shower, use a wipe or clean wet cloth to wipe your skin that was not covered by clothing.

Source: Ready.gov

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