(MercuryNews) - Officials say a worker at a Central California winery has died after being exposed to ammonia. Sanger police spokeswoman Cpl. Jaimy Gaines says the man was one of six workers exposed early Tuesday morning at a winery operated by Gibson Wine Co. Gaines says the other workers tried to rescue the man but were unable to get to him because of the fumes. It was not clear how the ammonia was released. Officials say the man, identified as Robert Munoz, of Sanger, died at the scene. The other employees were treated and released. Sanger fire officials, workplace safety authorities and county environmental officials are investigating the case.