Near Petersburg, Ind., workers are now completing construction of a 620-foot-tall chimney for Indianapolis Power and Light Co. (IPL). To comply with federal clean air requirements, IPL, like many power companies, had to install scrubbers to remove sulfur oxide pollutants from the plant's emission gases. These scrubbers required a new chimney, and IPL chose brick as the material to line the chimney's flues. As they wash the flue gases by injecting neutralizing agents into them, the scrubbers also make the gases much cooler and moister. This causes any sulfur still in the gases to condense inside the chimney as sulfuric or sulfurous acid. "These acids can eat through a 3/8-inch steel liner in a matter of months," say one chimney consultant. That's why most power companies build their liners out of brick. Brick flue liners resist the acids in power plant gas emissions at less cost than any other system. But they can't always be used. They shouldn't be used in Seismic Zones 3 and 4. For chimneys taller than 1,000 feet, they may not be economical to build. And some power plants lack the space brick liners require. Even so, industrial chimneys are the greatest user of chemical-resistant masonry. In the next five years, as older plants go out of phase and as developing areas require more power, some people expect an upswing in new production.