I was the driver operator on the first due Engine at a major fire. We had Semi trailers and piles and piles of electronics and bunks of wood all burning in about 3 feet of dry cheat grass (flashy fuel). We had a civilian that would not leave the fire ground and was hampering the efforts of my hose team. The team was requesting to get the man removed from the area. I was wearing only my bunker pants and duty shirt . I left my pump panel with the IC’S permission and entered the fire ground. I was half way in the fire ground when a 55 gal barrel exploded and sent a 200 ft fire ball in the air. I was about 15 feet from the barrel when it exploded. I immediately left the fire ground and put on all my PPE including my Scott air Pack. The civilian died of a heart attack 25 mins later in the fire ground area. He was pulled out and worked by the crew that he was hampering.