The deadly ice storm that gripped the north-eastern US and eastern Canada last month was nothing unusual for the Z-40 turbines operated by Green Mountain Power (GMP) in Vermont. The weather was so extreme, it was even described as North America's most expensive natural disaster ever. The freeze buckled entire electric pylons and left many people in Quebec, Vermont and other areas without power and other necessities for days. But the 11 Zond turbines atop Waldo Mountain near Searsburg weathered the storm easily, says GMP's John Zimmerman. "There was ice at the site but it didn't affect operations," he adds. Two or three days after the storm, he visited the site and found the turbines completely covered with a layer of clear ice between three-quarters of an inch and an inch thick -- but still producing power, he reports. The plant was designed to withstand extreme freezing, which hits the site every winter: among other measures, the blades are coloured black to help offset low temperatures. Temperatures were also harsher at ground-level than at higher elevations -- an unusual storm characteristic. "The turbines routinely run with ice," says Zimmerman.