Sometimes flames rise up out of nowhere and threaten to burn your food. This usually happens when excess fat from meats you're cooking falls onto the embers and ignites them. To avoid, this you should try to remove as much fat as possible from your meats before placing them on the grill.
To calm the flames, keep a water bottle nearby. The ones with a sports cap work best because they give you more control over where to squirt the flames that come up.