Why Your Microwave's Metal Rack Is Safe (But Other Metals Spark)

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Your mom always told you not to put metal in the microwave, and you've lived your whole life in fear that you might accidentally leave a fork on a plate you are reheating or forget to take the foil off that leftover casserole, causing your house to explode. So now that you want to purchase a microwave, why do you see so many models with metal-looking wire racks inside? Don't worry, the microwave industry isn't gaslighting you. There is a reason why their racks can be zapped, but that other types of metal are potential problems. These racks won't create sparks when hit by electromagnetic waves, which are what cause fires to start. 

As University of Virginia physicist Louis Bloomfield told the podcast Science Update, metal and microwaves aren't incompatible, and the inside of microwaves are actually made of metal. This metal reflects microwaves onto your food, which heats it, but doesn't create sparks. That's because, as YouTube Huffpost explains, it's not about the kind of metal used but the shape of the item that has everything to do with fire risk. Blunt, flat shapes won't produce sparks, but sparks, and maybe fire, will occur if electromagnetic waves hit sharp edges like the tines of a fork or crumpled edges of foil. The metal racks that come with microwaves are designed to be thick and blunt enough to safely reflect these waves without sparking. 

You can use that metal grilling rack that came with your microwave to better evenly cook your food, and racks can also be helpful to cook more than one dish at a time. If you like the idea of space-saving or better heating, but your microwave didn't come with a rack, you shouldn't just add one from your other cooking accessories to get these benefits. You simply can't be sure that the rack you put in will be compatible and designed in a way to avoid sparks. 

To further complicate the issue, even some microwaves that come with racks as accessories have warnings about when you can and cannot use them. Some modern types of microwaves on the market are combination cookers, with modes like air frying or convection baking, and come with accessories like metal baking racks or trays. For example, this Toshiba Air Fryer Combo 8-in-1 Countertop Microwave Oven includes a removable baking rack and tray, which the instruction manual says can only be used when the microwave is in grill or convection cooking mode, and not when used as a microwave. To be safe, you should always consult with your manual to see exactly what materials should and shouldn't be used inside your specific model of microwave, whether it came with a metal rack or not.