Both people and lightning-sensitive industries may be in more danger than they realize, according to a researcher who says the hazards of electrical storms have been underestimated.

Lightning strikes the earth much more often than weather records based on observers' reports indicate, says Stanley A. Changnon in the Journal of Geophysical Research-Atmospheres."Those who have to worry about the risk of lightning damage, for example, nuclear power plants, have had to use data based on (thunder records) to develop their risk analyses," Changnon said in a telephone interview.

"It's very clear that thunder rather dramatically underestimates the frequency of lightning near a given point."

Changnon discovered by using electromagnetic detectors to record actual cloud-to-ground flashes that between 22 percent and 40 percent of lightning flashes occurred at times when no thunder was heard.

"It is not good news," he said.

Changnon, a researcher affiliated with the Illinois State Water Survey, also teaches at the University of Rochester in Rochester, N.Y. His report was done in conjunction with his son, David Changnon of Colorado State University and Richard B. Pyle of the State University of New York at Albany.

Detailed thunderstorm records go back to the late 1800s, Changnon explained, but they have always depended on the reports of trained observers, primarily listening to the thunder generated by lightning.

In recent years, however, electromagnetic detectors have been installed in many areas to record actual lightning strokes.

The researchers compared reports by weather observers with the lightning records from sensors used by the federal Bureau of Land Management in Western states and by electrical utilities along the Eastern seaboard.

"The degree of relationship is relatively weak," Changnon reported. "It gives one a lot of pause, in many respects, about how the atmosphere works, how good our weather records are and how safe we are."