I am just a noob to mining, but I know dust buildup in old laptops can stop them working and shorten their lives. Maybe the same thing can happen to a graphics card. If you want to safely remove the dust from a laptop you have to buy a special electronics wriststrap which has a wire coming off it to conduct electrostatic electricity built up on your body to the ground. You attach the wire to some safe ground point like a copper water pipe.

If you take the back off a laptop without one you risk frying the electronics. It might be worth buying a cheap one off ebay for a few dollars then checking your graphics card while wearing it.