Today's the 13th, a good day to be extra careful. Actually, any day's a good day for safety. So, today is a good time to learn about tempered glass -- what it is and why and where it's used. When standard glass breaks, it breaks into "shards," large dagger-like pieces. Tempered glass (due to various types of heat-treating), breaks into tiny pellets. It is stronger, too, and therefore is much safer overall than standard glass. That's why tempered glass is used or required wherever potential danger from breakage exists. This includes glass in doors, tub enclosures, skylights and some windows. Some appliances utilize tempered glass, too, as do automobiles in both side and rear windows. Safety glass used in windshields is different. It has plastic film between two panes of glass that holds everything in place when it shatters. For home use, there's a lightweight, inexpensive safety alternative: clear plastic panels called Plexiglas. They're used for everything from picture frames to storm doors. And that's the On The House tip for today.