If a barbecue grill is left out in the rain or in high humidity for a long period, rust might develop on the grill. While rust is certainly unsightly, a little bit of rust on your grill shouldn't be cause for too much concern. However, proper maintenance should be performed to ensure that the problem doesn't get any worse.
Whether or not rust is safe depends entirely on how much rust a person ingests. If you visually inspect your grill and don't notice rust but there is a hidden flake or two that falls off on your food, you will almost assuredly be fine. On the other hand, a very rusty grill could deposit large amounts of rust onto your food, which isn't very healthy, and according to Dr. Carlo Rosen of the Beth Israel Deaconess Medical Center, can cause damage to your intestinal tract.
When grills become rusty, you need to clean them to ensure that you have a food-safe surface to cook on. If the rust is flaking, use a scraper to clean off the grills. Using a wire brush, vigorously attack the grill until you've restored it to a completely clean surface. Rinse off the grills to ensure that no rust flakes are left behind when you start cooking.
One good way to keep rust off the grill is to ensure that a layer of oil stays on the grill at all times. After you clean a grill thoroughly, you should spray it with some oil to keep it from rusting. Alternatively, after you cook on the grill, you should always clean it well enough to remove any char or food, but don't worry about scrubbing it absolutely clean until the next time you're about to cook. Natural food oil will coat the grill from cooking and protect it from rust.
Replacing the Grill
To prevent rust even more effectively, replace the grill in your barbecue. Certain types of grills resist rust much better than others. Find a stainless steel or porcelain-coated grill set to the right size to fit in your barbecue, and replace your old grills if they get especially rusted. The new grills will stay clean and rust free with much less hassle than cast iron grills.