Turning Up the Heat

A reader asks The Green Guide:

A few weeks ago I used a Glad OvenWare plastic container that was supposed to be safe up to 400 degrees. I cooked with the temperature of 300 degrees and used a cookie sheet per the package instructions. The container melted, flamed, smoked up something awful and gave off fumes that were terrible. I am an asthmatic among other things and had a very bad time breathing until I got the oven out of my house and replaced. Is there a way to find out if the fumes were truly harmful?
Sincerely,
Jean West

The Green Guide responds:

Thanks for your question. We contacted Glad with your concerns and were told that the containers are made with a plastic resin called crystalline polyethylene terephthalate (CPET), which is similar to the #1 PET plastic used in plastic soda and water bottles. CPET has a chemical structure similar to PET but contains polypropylene fibers (#5 plastic) added during manufacture to make it more rigid and glass-like.

One of the safest plastics on the market, CPET is, nonetheless, a plastic, made from ingredients derived from petroleum and natural gas. When plastics melt, it's similar to burning these fuels in your home, and the fumes you experienced are not uncommon when plastics are melted. CPET is made from ethylene glycol and terephthalic acid, both of which, in vapor form, have been known to irritate respiratory tracts and could pose problems to people with sensitized respiratory systems, such as yours. In addition, other types of PET plastic, like the trademarked fiber Mylar, have been found to release the air pollutants and respiratory irritants carbon monoxide, acetaldehyde, methane and ethanol when melted.

While you probably didn't want any of those added "ingredients" in your cooking, it might be reassuring that the plastic used in Glad's OvenWare contains no plasticizers, such as the hormone disrupting phthalate di-2-ethylhexyl adipate, or chlorinated compounds that may contain carcinogenic dioxin, both of which are found in #3 polyvinyl chloride plastics and pose serious health threats when #3 plastics are melted.

"CPET has been used in the food industry for over 20 years," says Ed Tucker, associate research fellow at the Glad Products Company, which manufactures Glad OvenWare. "It's the same plastic used in frozen food containers designed for the microwave." And when used as the package indicates, it shouldn't release the aforementioned chemicals into your home. Designed to withstand higher temperatures than conventional PET, CPET has a melting point approaching 500 degrees F. Tucker is quick to point out, however, that the maximum temperature at which OvenWare should be used is 400 degrees, as you read on the packaging. "The product is plastic," he says, "and it can melt with excessive heat. That's why we recommend preheating."

The issue of preheating may be one reason your product melted and flamed. "Ovens don't heat themselves gradually," says John Drengenberg, consumer affairs manager at Underwriters Laboratory. Instead, he says, when you set your oven at a certain temperature, the oven goes through varying heating and cooling cycles, with a sensor turning the heating element on and off as needed until your desired temperature is reached. Since these containers can withstand a maximum temperature of 400 degrees, says Tucker, there's the possibility they might melt during one of these first heating cycles, which, he adds, "is the worst time that you can get drastic temperature spikes."

Your use of the container on the cookie sheet is laudable, since that too helps regulate temperature and protects the plastic from overheating. Tucker adds that keeping the container full of food, which "acts as a heat sink," and using only one container at a time prevent them from melting as well.

If all this seems like a lot of effort, it's worth considering that, in addition to your lungs, your energy bill could take a beating. Preheating an oven can pose an energy drain since you're heating empty space and because you have to open the door once the temperature is reached; that can drop the oven temperature as much as 50 degrees. The Green Guide has also suggested doubling up and cooking multiple items at once to maximize energy efficiency, something that isn't recommended with OvenWare containers.

Sticking to tried-and-true glass and ceramic baking dishes is still the best alternative, but if you do choose plastic, opt for safer #1, #2, #4 or #5 plastics, which don't leach chemicals. And even those designated as "microwave-" or "oven-safe," should, as you've found, be handled with care and used in strict adherence to manufacturer directions.