The United States expanded its evacuation warnings for the area surrounding the nuclear reactors in Japan, now recommending that Americans in Japan stay at least 50 miles away. The recommendation, made Wednesday, differs from that of the Japanese government, which is warning its citizens to stay 12 to 18 miles away or to stay indoors if evacuation is not possible.
"The advice the Japanese government is giving based on the information it has is different than the advice we'd be giving if this incident happened in the United States," White House spokesman Jay Carney said Wednesday.
But some radiation experts say that depending on the type of radioactive event, staying indoors could be more effective at lowering your risk of radiation than widespread evacuation.
Radiation is a carcinogen, and high doses or long term exposure can increase the risk of cancer.
Both taking shelter in place and evacuating pose the same risk for radiation exposure, said Jonathon Links, director of the Center for Public Health Preparedness at Johns Hopkins Medical Center.
"Depending on the nature of the release, you have to weigh the options," said Links.
If there is an explosion or meltdown, causing a one-time release of high radiation levels rather than an ongoing release over a long period of time, shelter in place may be better than evacuation, said Links.
"If you're indoors during that one-time event, the plume will pass over while you're inside breathing uncontaminated air," said Links. "If you tried to evacuate you'd be outdoors, and depending on how mobile you would be and what direction you're evacuating, you might get significant exposure."
Some should also choose to create a shelter in place if they do not have enough time to evacuate ahead of a radiation release, according to Robert Whitcomb, lead physical scientist for the radiation studies branch in the division of environmental hazards and health effects at the Centers for Disease Control and Prevention.
One of the most important ways to protect oneself indoors is to make sure the contaminated air outdoors does not seep in. That means shutting turning off any ventilation systems that circulate air, unless you are in a modern building with a high-powered filtration system.
"Effectiveness of sheltering in place depends on the location of the shelter and how well the shelter can be isolated from the environment," said Dr. Ken Mossman, professor of health physics at Arizona State University.
High amounts of radiation can penetrate thinner walls exposed to the outside, so experts also advise moving to the middle of a house or office space.
The length of time to shelter in place depends on the severity of the exposure. But an emergency preparedness kit with at least three days worth of essentials should be on hand just in case. If you have an adequate supplies then in some cases it may be better to stay put than going outside and potentially risking a higher dose of radiation, said Links.