Today while mowing a small residential lawn I looked up to notice it was on fire. I quickly put it out using my trusty hat and then the water hose. It only burned up a small section. I talked to the fire dept. and they said it might have been caused by hitting a rock or something caused a spark. The grass was still mostly dormant and dry. My question is how common is this? Has it happened to anyone else? The customer took it ok. I'm afraid that I will worry that I left the back yard on fire or something on all my future yards. Thanks for your help.