Will a Cold Fridge Glass Shelf Break if You Put a Hot Container of Food on It?
Refrigerator shelves are made of tempered glass, which is much more resistant to heat and cold than untempered. Also, if tempered glass breaks, it shatters into very small, squarish pieces with no sharp edges, rather than the lethal shards that can be the result of normal glass shattering. This greatly reduces the risk of injury if you do happen to break a glass shelf.
Putting a hot container full of hot food onto a glass shelf in a refrigerator will not cause the shelf to break, but it will cause the refrigerator to work hard and use more electricity as it tries to cool down the food. It's preferable to leave the container on the kitchen counter for an hour or two before putting it into the refrigerator.
While heat will not break a piece of tempered glass, it is possible to break a glass refrigerator shelf by scratching it or giving one of its edges or corners a hard jolt. Be very careful when you take the glass shelf out of the refrigerator for cleaning. Wipe it down with hot soapy water using a sponge or dishcloth, then rinse it off and let it air dry. When you put it back into the refrigerator, be sure that it is properly inserted into its mounting tracks and not sitting directly on top of the vegetable drawers underneath it.
If you do have the misfortune to break the glass shelf in your refrigerator by dropping, jarring or scratching it, you have several options for replacing it. You can have another tempered glass shelf made at a glass store, although this is quite expensive. Alternatively, you can replace it with a thick and rigid piece of plexiglass to retain its see-through character, or in a pinch you can replace it with a piece of plywood that's cut to fit.
Rather than putting a hot container directly into the refrigerator, consider transferring the food that's in it into several smaller, sealable containers. The separation of the food into smaller bits will speed its cooling time, and the sealable containers will keep it fresh for longer. Also, the multiple containers will distribute the weight of the food more widely across the shelf, making breakage even less likely.