BERKELEY, Calif.- On a windy rooftop overlooking the misty expanse of the San Francisco Bay, a squat metal machine scours the air for signs of dangerous radiation.
Most of the time, the machine's white filters don't pick up much more than dust. But when things go wrong, such as the recent nuclear accident in Japan, it stands ready to give the alarm.
''Nine times out of 10, if not 99 times out of 100, all we're finding is natural background levels, but we have this system in place for a reason,'' says Leo Kay of the U.S. Environmental Protection Agency which runs the radiation check program. ''There's a lot of concern over possible exposure to radiation and it's something that we intend to continue monitoring.''
The latest nuclear scare happened 70 miles northeast of Tokyo when workers at a nuclear plant put too much uranium into a bucketlike container, setting off an uncontrolled atomic reaction that continued for hours. At least 49 people were exposed to radiation.
Following the accident last Thursday, air sample checks were increased from roughly twice a week to daily. However, no unusual levels of radiation have been detected and health officials don't expect they will be due to atmospheric conditions and the relatively small amount of radiation released in the accident.
Another nuclear accident occurred Monday when radioactive water leaked inside a South Korean nuclear power plant, exposing at least 22 people to radiation, but government officials said radiation did not leak outside the building.
The Berkeley air sampler is part of a 55-station network run by the U.S. EPA in a program known as the Environmental Radiation Ambient Monitoring System, or ERAMS. Other West Coast sampling stations are located in Los Angeles, Portland, Ore., Olympia, Wash., Spokane, Wash., Alaska and Hawaii.
Seen up close, the air sampler fixed to the roof of the state health services department in Berkeley is a humble device that mainly consists of a pump that sucks air through a round filter. Twice a week (or daily in the case of special events) the filters are sent off to a lab for analysis.
Also on the roof is a sink-like affair used by ERAMS to sample rain and another air sampler that is part of a state radiation monitoring system.
The ERAMS program goes back to 1973, regularly sampling air, precipitation, drinking water and milk. In the early days, the testing was partly to check for fallout from aboveground nuclear testing. These days, it's to check for the impact of nuclear emergencies like the Japan accident and to provide a baseline for comparisons.
So far, the only elevated levels of radiation turned up by ERAMS happened after the 1986 explosion of a reactor at the Chernobyl nuclear plant in the Ukraine, said Ed Sensintaffar, director of the National Air and Radiation Environmental Laboratory in Montgomery, Ala.
''Essentially, nuclear fallout that resulted from that event was primarily small particles that got up into the upper atmosphere and it really only came out in significant quality when it rained,'' he said. Even then, the amounts were still so small they were not a significant increase over natural radiation levels, he said.
Officials now are revisiting the ERAMS program, to see if stations need to be moved due to population shifts.
Craig Conklin, director of the Center for Risk Modeling and Emergency Response for the EPA in Washington, said the program is worth continuing.
''It helps develop what we determine the background level of radiation in the U.S. so that, God forbid, something should happen we would have comparisons.''