Last week (12/21) the Today Show broadcasted an alarming demonstration of Pyrex glass exploding after being subjected to certain combinations of conditions. See NBC News’ detailing here . As reported in this American Ceramic Society Bulletin , some scientists believe that changes to the material (replacing borosilicate with soda lime silicate) weakened the glass. However, makers of Pyrex disagree vehemently with these conclusions—see their side of the story here.
It turns out that hot Pyrex pans set directly on a wet or cool surface, such as a granite counter-top, undergo a sudden temperature change that produces some risk of it shattering. That strikes close to home for me, having re-done our kitchen (as is the style nowadays) with granite. Fortunately, being accustomed to plastic (Formica) countertops, I always put down cloth potholders before setting down the hot Pyrex pan. The take-home message is being careful not to subject Pyrex to rapid increases or decreases in temperature. See this site for safety instructions.
PS. On a lighter note (literally: too much sun) regarding heat and silica (main constituent of sand) see this New York Times news making it official that the hottest temperature ever recorded is 134 degrees F in Death Valley. They are pyre Rex.