"People are awakening to the threat," Packer said. "A lot of it is the terrorist attacks, a lot of it is the economy. People are concerned about having a government failure. Some of it is Earth changes."
Brian Duvaul, the sales manager at American Safe Homes, said that in the last quarter of 2012 his businesses saw a 25 percent jump in calls that he attributed, in part, to the Mayan calendar ending and fears about the end of the world. He also said he had previously seen jumps in sales during the anthrax scares of 2002 and 2003, and after the Fukushima nuclear plant meltdown in Japan in 2011.
"People don't always come out and tell us why they're doing what they're doing. We had one guy tell us he had to get a blast door for his wife's birthday, which happened to be one day before the Mayan calendar ended," Duvaul said. "I didn't believe him, but we got him the door.
Bomb shelter manufacturers said that their average customer is a middle-aged, affluent man, though beyond that, all different types of people have come looking for protection from future disasters.
"The purchasers, they understand the need for it. It's almost like buying insurance. You don't know if we'll have a scenario in our lifetime, though we suspect it, that will drive us underground," Roberson said.
"It seems to be not as much about fallout," he said, explaining the motivation for installing a shelter. He said that logically, most people won't be within range of nuclear fallout,
"It won't matter how close you were to the blast radius. It's going to be the 'haves and have-nots', and if they need it they're going to take it, to come into your house and burn it down," he said.
Packer of Utah Shelter Systems said that of her customers, she has seen few traditional "survivalists," and many more ordinary, highly-educated professionals coming to her in case of a worst-case scenario.
"The vast majority are professionals," Packers said. "They are very well educated, a lot of doctors. The majority of them are physicians, and attorneys, a lot of engineers, all of whom understand the real threat."
Spencer Weart, the author of the "The Rise of Nuclear Fear," said that bomb shelters are a logical act for people who really believe there will be a nuclear war or some type of disaster. Weart has catalogued America's nuclear fears dating to the 1950s.
"It's a way of putting money where your mouth is, isn't it?" Weart said. "If you believe there's actually going to be a nuclear war, you're kind of in a tough situation. If you're convinced of that, it makes sense to make yourself a fallout shelter. So most people convince themselves there isn't going to be a nuclear war. It's optimists versus pessimists."
The rise in popularity of bomb shelters shows a persistent strain of skepticism about community in America, he said.
"The thing about a bomb shelter is it assumes a societal breakdown, and this is one of the great myths that's been propagated since the 19th century, that society will break down and it's every family for himself, which is not what happens in a disaster," Weart said.
"People tend to pitch and help each other, even at Hiroshima and Nagasaki. It ties in a fundamental distrust of human nature. It shows a complete distrust in society and the social system."