PHOENIX -- One man died and another was badly burned after an RV caught fire Tuesday afternoon.The Phoenix Fire Department responded to a report of an RV on fire near 27th and Northern avenues. First arriving firefighters encountered a 29-year-old man with severe burn injuries standing in front of a fully engulfed RV. The man was yelling for help, saying another man was still inside."He tried hitting on the windows on the RV and it was just flames all over," witness Gabriela Acosta said. "There was nothing they could have done."The 29-year-old man received second- and third-degree burn injuries to his upper body. He was transported to the Arizona Burn Center and is expected to survive.Firefighters attempted to rescue the other man while also extinguishing the fire, but he had succumbed to smoke and burn injuries. He has been identified as Kenneth Moore, 57.The men were making repairs on the RV and test-driving it when they heard a big boom. The vehicle then went up in flames."I've never seen something burn that fast before," said Michael Hawkins, who called 911.The younger man had known Moore his entire life and referred to him lovingly as uncle.An investigation is underway to determine the cause of the explosion.