Consumer Reports: Hot Glassware Can Shatter Unexpectedly

Dec 07, 2010, 06:28 ET from Consumer Reports

Consumers Union Asks Consumer Product Safety Commission to Investigate Glass Bakeware

YONKERS, N.Y., Dec. 7, 2010 /PRNewswire-USNewswire/ -- A year-long investigation by Consumer Reports reveals that while hundreds of millions of glass baking dishes are used safely each year, hot glassware can shatter unexpectedly, sometimes causing serious injuries.  The report details several stories of glass bakeware breaking and shattering, leading off with the story of a grandmother on Thanksgiving Day who said she opened her oven to baste a ham only to have the glass dish shatter, sending pieces of glass and hot juices flying.  

After reviewing scores of consumer reports filed with federal regulators about bakeware unexpectedly shattering, Consumers Union (CU), the nonprofit publisher of Consumer Reports, has  asked the Consumer Product Safety Commission (CPSC) to conduct a thorough study of glass bakeware on the market.  CU has also called on manufacturers to imprint warnings that are clearer and more prominent on their bakeware.  "Part of the problem is that the fine print warnings are so tiny and they're part of the packaging that consumers often throw out," said Andrea Rock, senior editor, Consumer Reports.    

The report is available in the January issue of Consumer Reports and online at  In a typical year, the two main manufacturers of glass bakeware, World Kitchen, the maker of Pyrex in the U.S., and its competitor, Anchor Hocking, collectively make on average more than 70 million units of what is undoubtedly a staple of most kitchens and a popular  cooking tool when preparing holiday meals.  

The report contains ten precautions that may surprise cooks who have used glass bakeware.  To minimize the chances of the glassware shattering, consumers should read and save the safety instructions from their glass bakeware and follow these safety rules:  

  • Always place hot glassware on a dry, cloth potholder or towel.
  • Never use glassware for stovetop cooking or under a broiler.
  • Always allow the oven to fully preheat before placing the glassware in the oven.
  • Always cover the bottom of the dish with liquid before cooking meat or vegetables.
  • Don't add liquid to hot glassware.
  • If you're using the dish in a microwave, do not use browning elements, and avoid overheating oil and butter.
  • Do not take dishes directly from the freezer to the oven or vice versa.
  • Never place hot glassware directly on a countertop (or smoothtop), metal surface, on a damp towel, in the sink, or on a cold or wet surface.
  • Inspect your dishes for chips, cracks, and scratches. Discard dishes with such damage.
  • To avoid risks associated with glass dishes, consider using metal bakeware for conventional and convection ovens.

To find out about glass bakeware, Consumer Reports conducted an investigation that included testing in Consumer Reports' labs and outside labs, and gathering information from manufacturers, government agencies, experts, and consumers.   When Pyrex was first marketed in 1915, it was made of a heat-resistant glass called borosilicate that previously was used to prevent glass railroad lanterns from shattering.  While U.S. manufacturers of both Pyrex and Anchor Hocking have switched from borosilicate to soda lime glass for their glass bakeware, the magazine notes, samples of European-made glass bakeware obtained by Consumer Reports continue to consist of borosilicate.  The manufacturers say their soda lime glass has advantages and is less likely to break when dropped or bumped.  While the results from Consumer Reports' limited impact tests were highly variable, some samples of soda lime glass showed the highest impact resistance.

Consumer Reports tested both types of glass in its lab to see how they compared in extreme conditions likely to cause breakage.  To test the dishes, Consumer Reports filled each pan with dry sand (which gets much hotter than food) and then placed the dishes in ovens set at varying temperatures.  The testers then compared what happened when each hot dish was removed from the oven and placed on a wet granite countertop, a situation likely to induce thermal shock and contrary to each manufacturer's instructions for use.  Consumer Reports notes that the bar was set high in the extreme tests because dishes that are scratched or damaged may not offer the same safety margin as new dishes, and users may ignore or be unaware of the usage instructions.  Ten out of ten times the soda lime glass broke after baking at 450 degrees. But in the same conditions, the European borosilicate glassware did not break, though most did after baking at 500 degrees.  

Some key highlights from the investigation include the following:

  • Consumers in scores of cases reported glass bakeware unexpectedly shattering, according to federal documents, court papers, and interviews.  When Consumer Reports examined 163 incidents (152 of which were from CPSC files) in detail, the analysis revealed 42 reports of injuries, ranging from minor burns or cuts to those requiring surgery. More than half of the incidents reportedly occurred while the bakeware was in the oven while almost a quarter occurred with the bakeware cooling on a counter or stovetop.  
  • When glass bakeware does shatter, consumers report, it can break into sharp shards that go flying, raising the risks of injuries. This contrasts with claims from one of the manufacturers that its glass bakeware breaks into "relatively small pieces generally lacking sharp edges."
  • Consumers Union (CU), the nonprofit publisher of Consumer Reports, says  manufacturers should imprint clearer and more prominent warnings on their bakeware, not just on the packaging that gets tossed upon first use.  While hundreds of millions of dishes are used safely each year, CU believes the situation is serious enough that it has asked the Consumer Product Safety Commission (CPSC) to conduct a thorough study of glass bakeware on the market, with particular attention to the difference between bakeware made of soda lime glass and borosilicate.  CU also urges consumers who experience glass bakeware unexpectedly shattering to report the incident to the CPSC at 800-638-2772 or  


The material above is intended for legitimate news entities only; it may not be used for advertising or promotional purposes. Consumer Reports® is published by Consumers Union, an expert, independent nonprofit organization whose mission is to work for a fair, just, and safe marketplace for all consumers and to empower consumers to protect themselves.  We accept no advertising and pay for all the products we test. We are not beholden to any commercial interest. Our income is derived from the sale of Consumer Reports®,® and our other publications and information products, services, fees, and noncommercial contributions and grants. Our Ratings and reports are intended solely for the use of our readers. Neither the Ratings nor the reports may be used in advertising or for any other commercial purpose without our permission. Consumers Union will take all steps open to it to prevent commercial use of its materials, its name, or the name of Consumer Reports®.

SOURCE Consumer Reports