Alarmed officials are warning of a “worst-case scenario” after 50,000 people have been ordered to leave their homes as authorities urgently try to stop a chemical tank from exploding. Firefighters have been spraying the outside of a tank at a company site in Garden Grove in Southern California with water hoses in an effort to cool the chemicals heating up inside and prevent an explosion. With the pressure building , Lee Zeldin, head of the US Environmental Protection Agency, said Sunday the “