Safety Concerns With Glass Bakeware

by Diane, M.P.H, M.S.

In recent years there have been several reports of glass bakeware unexpectedly shattering and, in some cases, causing serious injury. The number of consumers who have reported that their Anchor Hocking or Pyrex glassware broke unexpectedly is small compared to the billions of pieces of Anchor Hocking and Pyrex glassware safely and reliably used in American kitchens for generations. However, cooks and their families must heed certain precautions to reduce the risk of serious personal injury or property damage when using any glass bakeware (4).

 

Glass bakeware before 1980:

In 1915, Corning Glass Works introduced Pyrex kitchenware made with borosilicate glass, a type of glass made with silica and boron oxide. Borosilicate glass had first been made by the German chemist and glass technologist Otto Schott in 1893, 22 years before Corning produced the Pyrex brand (3, 6).

Borosilicate glass is known for being more resistant to thermal shock and less affected by thermal expansion or stress than any other common glass. Consequently, it is commonly used for the construction of reagent bottles used in laboratories. Borosilicate glass is sold under such trade names as Pyrex and Simax (3).

For years, cooks have safely used billions of pieces of Anchor Hocking and Pyrex glass bakeware made from borosilicate in the kitchen. Such kitchenware is generally durable, reliable, safe, and convenient for baking, serving, and storing leftovers, all in the same dish, when used according to the manufacturer’s directions.

Glass bakeware after 1980:

While European glass bakeware has always been and still is made from borosilicate, a change took place in the American glassware industry during the early 1980s. Tighter U.S. air pollution regulations and the need to reduce energy consumption caused a shift from using borosilicate to soda lime for the manufacture of glass bakeware, according to Philip Ross, a glass industry consultant in Laguna, Niguel, California. To comply with these regulations and still produce a safe and durable product, the Anchor Hocking Company changed its manufacturing process of glass bakeware, about 30 years ago, from annealed borosilicate to tempered soda-lime-silicate. Although Corning Incorporated began making some Pyrex glassware from soda lime during the 1940’s, older, clear-glass Pyrex manufactured by Corning before 1998 and Pyrex laboratory glassware has always been made of borosilicate glass (6). The European manufacturer of Pyrex, Arc International, still uses borosilicate glass in its Pyrex glass kitchen products; however, the U.S. manufacturer of Pyrex kitchenware uses tempered soda-lime glass. Therefore, Pyrex can refer to either soda-lime glass or borosilicate glass when discussing kitchen glassware, while Pyrex, Bomex, Duran, TGI and Simax all refer to borosilicate glass when discussing laboratory glassware.

 

In 1998, World Kitchen, a U.S. company based in Rosemont, Illinois, purchased the Pyrex consumer products business from Corning Incorporated. World Kitchen claims that it did not alter the product composition for Pyrex glass bakeware, has always manufactured Pyrex glass bakeware in the U.S., uses the same soda lime plant in Charleroi, Pennsylvania, to make Pyrex glass bakeware that Corning Incorporated used, and has not changed the manufacturing process or soda lime composition.

Pyrex glass cookware manufactured by World Kitchen is made of tempered soda-lime glass instead of borosilicate. World Kitchen supports this change, because soda-lime glass is cheaper to produce, the most common form of glass used in U.S. bakeware, and has higher mechanical strength than borosilicate — making it more resistant to breakage when dropped, which the company claims is the most common cause of breakage in glass bakeware. However, unlike borosilicate, it is not as heat-resistant (6).

The differences between Pyrex products depending on manufacturer have led to safety issues. The Consumer Product Safety Commission has stated that from 1998 to 2007, almost 12,000 people went to emergency rooms for treatment of injuries from glass bakeware that was dropped and broken, or shattered during use. The Commission has also received complaints that World Kitchen-produced Pyrex glassware has shattered at high temperatures. While shattering at high temperatures may be less common than breakage from being dropped, it poses a greater threat to consumers, since the glassware may break without warning. Consumer Reports magazine reviewed these complaints and determined that all of the bakeware users had assumed their bakeware would have the same characteristics and strength as the older borosilicate counterparts (4, 6).

Borosilicate versus tempered soda-lime glass:

While both borosilicate and soda lime are appropriate compositions for glass bakeware, heat-strengthened soda lime is more resistant to “impact breakage” – the far more likely cause of consumer injury, according to national emergency room data.

While more resistant to heat and thermal shock than other types of glass, borosilicate glass can still crack or shatter when subjected to rapid or uneven temperature variations. When broken, borosilicate glass tends to crack into large pieces rather than shattering. According to the Consumer Product Safety Commission’s National Electronic Injury Surveillance System data, consumers are far more likely to be injured by dropping glass bakeware than from breakage caused by sudden or uneven temperature changes.

Today, all U.S. manufactured glass bakeware, regardless of manufacturer, is made from tempered soda-lime-silicate glass. This is because, on the rare occasions when it does break, it tends to break into small pieces without sharp edges. Tempered or heat-strengthened bakeware is designed to strengthen the glass to be more durable and stronger than other glass products. A similar, although not identical tempering process is used for other glass products where safety is also important, such as automobile windows, sliding glass doors, and shower doors. As a result of this tempering process, when tempered bakeware breaks, similar to other tempered safety glass products, it breaks into a number of pieces, most relatively small, although some may be larger. Unlike non-tempered glass products, these pieces generally lack sharp edges when it does break, resulting in a lower likelihood of severe cuts from the broken glass. But when a product fails, it releases a small amount of energy, which can result in a loud sound and the glass can travel outward.

 

Three primary risks associated with using glassware for cooking:

  • Breakage due to a sudden temperature change applied to the glassware.
  • Breakage due to impact if the glassware is dropped or knocked against a hard object.
  • Burning when handling hot bakeware.

What causes glass bakeware to break?

Glass bakeware is a healthier alternative to metal bakeware because no hazardous materials leach into your food, and it helps to retain moisture and cooks more evenly than metal bakeware. However, like all glass, it can break. Anchor Hocking and Pyrex bakeware are safe when their care and use instructions are followed. Regardless of safety measures taken by both companies to strengthen and ensure the quality of their products, misuse can lead to failure of the bakeware.

Anchor Hocking states that the vast majority of failures are due to mishandling or improper care of the product. The misuse often happens over time, and the actual failure may occur at a later date. A few examples of mishandling are (2):

  • Scouring or improperly cleaning the bakeware.
  • Causing severe thermal shock by adding liquid to a hot dish, placing a hot dish into dishwater, or placing  a hot dish directly on a countertop, rather than using pot holders, pad or trivet.
  • Discarding chipped, cracked, or noticeably scratched bakeware products.
  • Hard hits or impacts occuring during usage, washing, or storing.
  • Cooking at a higher temperature than 425 degrees F.
  • Using glass bakeware on a stove top, or in a broiler, or toaster oven.
  • Placing glass bakeware on a recently used or still warm stovetop burner.

All glass, whether soda lime or borosilicate, can experience thermal breakage if exposed to sudden or uneven temperature changes. Avoid the most common causes of thermal breakage by following four simple rules (2, 5):

  1. Always place hot glass bakeware on a dry, cloth potholder or towel. Never place hot glass bakeware on top of a stove, metal trivet, damp potholder or towel, or directly on a countertop or other cold or wet surface, or in a sink.
  2. Never put glass bakeware directly on a heat source such as a burner, hot range, grill, or under a broiler or in a toaster oven.
  3. Always allow the oven to fully preheat before placing glass bakeware in the oven.
  4. Always cover the bottom of the glass bakeware dish with liquid before cooking meat or vegetables. The liquid, whether chicken or vegetable stock, apple juice, or water, will keep the temperature of the baking dish even and your food moist and tender.

Follow these warnings from Pyrex and World Kitchen LLC to reduce the risk of personal injury or property damage, as well as, glassware breaking or shattering immediately or later (5):

  • Do not add liquid to hot glassware. This can cause a sudden temperature change.
  • If using a dish in a microwave, do not use browning elements, and avoid overheating oil or butter.
  • Do not take dishes directly from the freezer to the oven or vice versa.
  • Inspect your glassware for chips, cracks, and scratches. Discard items with such damage.
  • To avoid risks associated with glass dishes, consider using metal bakeware for conventional and convection ovens.
  • Avoid sudden temperature changes to glassware. DO NOT add liquid to hot glassware; place hot glassware on a wet or cool surface, directly on countertop or metal surface, or in sink; or handle hot glassware with wet cloth. Allow hot glassware to cool on a cooling rack, potholder or dry cloth. Be sure to allow hot glassware to cool as provided above before washing, refrigerating or freezing.
  • Oven must be preheated before inserting glassware.
  • DO NOT use on or under a flame or other direct heat source, including on a stove top, under a broiler, on a grill or in a toaster oven.
  • Add a small amount of liquid sufficient to cover the bottom of the dish prior to cooking foods that may release liquid
  • Avoid handling hot glassware (including ware with silicone gripping surfaces) without dry potholders.
  • Avoid microwave misuse. DO NOT use glassware to microwave popcorn or foods wrapped in heat-concentrating material (such as special browning wrappers), heat empty or nearly empty glassware in microwave, or overheat oil or butter in microwave (use minimum amount of cooking time).
  • Be careful when handling broken glass because pieces may be extremely sharp and difficult to locate.
  • Handling your glassware without an appropriate degree of care could result in breakage, chipping, cracking or severe scratching. DO NOT use or repair any glassware that is chipped, cracked or severely scratched.
  • DO NOT drop or hit glassware against a hard object or strike utensils against it.

To reduce the risk of glass bakeware shattering:

  • Read and save the safety instructions on the product’s packaging.
  • Instruct all family members in the proper care and use of glass bakeware to maintain its integrity and safety.
  • Always exercise care when using glass products, especially when cooking food at high temperatures.
  • Use appropriate protection for hands, such as potholders or gloves, when handling any hot glassware.

References:

  1. Anchor Hocking Consumer Affairs Department: Allows consumers to ask any questions about using tempered glass bakeware. Contact information for the Consumer Affairs Department: Anchor Hocking, 519 Pierce Avenue, Lancaster, OH 43130 (consumer@anchorhocking.com). Hotline Telephone: 1- 800-562-7511 ext.2478.
  2. “Anchor Hocking’s Safety Record.” Complete Care and Use Instructions are available  at http://www.anchorhocking.com/Bakeware_Facts.html.
  3. “Borosilicate Glass.” Wikipedia, The Free Encyclopedia. 01/28/12.
  4. “Glass Bakeware that Shatters.” Consumer Reports. Yonkers, New York. January 2011. pp. 44-48.
  5. “Glassware Safety and Usage Instructions.” (Source: “Pyrex Products-Making Cooking a Little Easier.” www.pyrexware.com)
  6. “Pyrex.” Wikipedia, The Free Encyclopedia. 02/22/12.
  7. Wolf, Barbara.”Statement to ABC News From Anchor Hocking.” Discussed on Good Morning America: 12/07/10. Originally announced by Barbara Wolf, Senior Manager, Marketing Communications, Anchor Hocking regarding January 2011 article in Consumer Reports on Tempered Glass Bakeware on 12/06/10.

 

{ 2 comments }

Tancil March 11, 2012 at 3:30 am

Pyrex bakeware has been a part of my kihcten for years due to its versitility, attractiveness and ease to clean. These dishes go directly from the oven to the dining table and kihcten sink without a glitch. Cleaning is easy since baked on food/grease comes off easily without much elbow grease.This particular set is was hard to pass up not only because of its usefullness but its great price. I bought one set for myself and the others for gifts. The red accents not only coordinate with my kihcten, they provide a welcomed nonslip feature to the glass handles. The detailed pie dish provides a nice presentation at the table and the mixing bowl is conviniently sized plus the beakered end is a welcomed feature. Overall a great product which I highly recommend.

Diane, M.P.H, M.S. June 19, 2012 at 4:36 pm

I agree with you that Pyrex bakeware has been a superb product through the years, for baking, microwaving, serving, and storing food in the freezer and refrigerator. My Pyrex bakeware has lasted for many years. I use it practically every day and have never had any problem. However, there have been so many accidents and injuries documented in recent years with the newer Pyrex products, that I felt obligated to research what had changed with the manufacturing process. I would rather educate the public to be aware of any risks, take precautions, and avoid injury, than sit back and do nothing, especially since so many of us grew up with this product and assume that it is still made the original way. As Benjamin Franklin had said:”An ounce of prevention is worth a pound of cure.”

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