A deadly batch of opiates has claimed the lives of four people in less than a day in Lowell, the city's fire department said today.Authorities suspect the "overdoses were a mix of heroin/fentanyl and cocaine/fentanyl," Lowell Fire Chief Jeffrey Winward said in a statement.The overdoses occurred over 12 hours. Authorities urge people to abstain from using opiates, but if addicts must, they ask them to do so in groups.