Sterilizing Kitchen Sponges/Washcloths

Monte took off to run errands and I'm hearing a beeping in the kitchen. Nowadays all appliances ding or beep when done, or when the refrigerator is not shut tight, and my washer and dryer 'sing'. I just checked - he'd put a sponge in the microwave to sterilize. I've heard that some types of sponges could catch fire, so check on yours. We put dishcloths and sponges in microwave for 3 minutes to sterilize. Monte's mom, who was always bleaching hers to sterilize, loved that tidbit of info. So I'm passing it on.