The famous military smoke screen was introduced on this day in 1923 in a test off Cape Hatteras to conceal ship and troop movements from enemy eyes. For land and sea battles it works great. But firing up a fireplace (after last winter's use and sitting all summer) can cause all sorts of unwanted problems, from red eyes and coughing to air pollution and carbon-monoxide poisoning. Before you hold a match to any logs, whether natural wood or natural gas, the Chimney Safety Institute of America urges homeowners to check flues and dampers for tightness, blockage, debris and buildups. Check yourself or hire a chimney pro. A chimney sweep will make sure everything is free, clear and shipshape. Otherwise, you might be in for a military-quality smoke screen of your own with explosive action and real live firemen battling your fire. And that's the On The House tip for today.