UNIONDALE — While most Long Islanders sought relief from hot and humid conditions on Friday, Nassau County firefighters brought the heat to the Barbecue Grilling Throwdown Competition. Teams from Rockville Centre, East Meadow and Bethpage vied to see who could grill the best burgers, chicken, ribs and other foods suitable for the open flames. With the Fourth of July holiday near, instructors on hand also offered fire safety advice.